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Right Parietal Lobe

From: Neuropsychiatry, Neuropsychology, Clinical Neuroscience
by Rhawn Joseph, Ph.D.
(Academic Press, New York, 2000)




THE RIGHT PARIETAL LOBE Font size=+2>

By Rhawn Joseph, Ph.D.

PARIETAL TOPOGRAPHY

There are nine major somesthetic areas within the parietal lobe, such that the primary, association, and assimilation areas actually consist of numerous subareas. Broadly, and most generally, however, the parietal lobe may be subdivided into a primary receiving area (involving Brodmann's areas 3ab,1,2) within the post central gyrus, an immediately adjacent somesthetic association area (Brodmann's area 5ab), a polymodal (visual, motor, somesthetic) receiving area located in the superior-posterior parietal lobule (area 7ab), a granular insular area which is located in the inferior convexity and encompasses part of the marginal gyrus, and a multimodal-assimilation area within the inferior parietal lobule (areas 7, 39, 40) which encompasses the angular and supramarginal gyrus.

The primary somesthetic as well as portions of the association area contribute almost one third of the fibers which make up the cortical-spinal (pyramidal) tract. Hence, this region is very involved in motor functioning; e.g., the sensory and postural guidance of movement, including hand movements and the direction of gaze (Cohen et al. 1994; Dong et al. 1994; Snyder et al., 1998). Moreover, the primary motor and somesthetic association regions are richly interconnected (Jones & Powell, 1970) with the primary areas transmitting to the association areas which in turn project to the motor cortex. Indeed, in order to make motoric responses with some precision, there must be tremendous sensory feedback concerning proprioception, including data regarding the positions of the various joints and tendons, etc. --information which is provided by the somesthetic cortices (Cohen et al. 1994; Dong et al. 1994; Lebedev et al. 1994; Pred'Homme & Kalaska 1994; Snyder, et al., 1998). Together, the motor and somesthetic areas comprise a single functional unit which some have referred to as the sensorimotor cortex (Luria, 1980).

THE PRIMARY SOMESTHETIC RECEIVING AREAS

The primary somesthetic areas consists of three narrow strips of tissue (areas 3ab, 1, 2) which differ histologically, in architectural composition, and in sensory input. Moreover, each of these areas maintains a complete and independent representation of the body (Kaas, 1993).

BODY IMAGE REPRESENTATION

The primary receiving areas for somesthesis continues up and over the top of the hemisphere and along the medial wall where the lower half of the body is represented. Specifically the rectum, genitals, foot and calf are located along the medial wall, the leg along the superior surface of the hemisphere, and the shoulder, arm, hand and then face along the lateral convexity (Penfield & Boldrey, 1937; Penfield & Jasper, 1954; Penfield & Rasmussen, 1950).

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Body parts are also represented in terms of their sensory importance, i.e. how richly the skin is innervated. For example, more cortical space is devoted to the representation of the mouth, fingers and the hand than to the elbow or trunk (Warren et al. 1986). In fact, the area devoted to representation of the fingers is 100 times larger than the area devoted to the trunk. Because of this the cortical body map is very disorted. However, as noted, some areas are also juxtaposed, such as the hand and mouth area.

In summary, the primary receiving area receives very precise information regarding events occuring anywhere along the internal/external body and responds to converging inputs from muscle spindles, cutaneous and joint receptors, as well as proproceptive and vestibular stimuli. In this manner, not only the body but the global properties of objects held in the hand can be determined (Iwamura & Tanaka, 1978); i.e. stereognosis.

FUNCTIONAL LATERALITY

As detailed in Chapter 10, there is clear evidence that the right parietal area is dominant in regard to many aspects of somesthetic information processing. Hence, neurons in this half of the brain appear to be more sensitive and more responsive and to more greatly monitor events occuring on either half of the body, but particularly the left. In fact, this relationship was noted over 150 years ago by Weber.

According to Weber (1834/1977), the left half of the body exceeds the right in regard to most forms of tactual sensitivity. The left hand and the soles of the left foot, as well as the left shoulder are more accurate in judging weight, have a more delicate sense of touch and temperature, such that "a greater sense of cold or of heat is aroused in the left hand" (p. 322). That is, the left hand judges warm substances to be hotter, and cold material to be colder as compared to the right hand, even when both hands are simultaneously stimulated.

THE BODY IN SPACE

Signals from joint and cutaneous receptors are transmitted to association neurons (Skata & Iwanura 1978). Many associaton cells also receive converging input from primary neurons concerned with different body parts (Dong et al. 1994; Sakata, et al. 1973), and can combine these signals with visual information (Snyder et al., 1998) and are thus able to determine positional interrelationships.

For example, a single association neuron may receive information regarding the elbow and the shoulder, and become activated only when these two body parts are simultaneously stimulated or in motion. A considerable number of cells are especially sensitive to the posture and position of the trunk and extremities during movement (Hyvarienen, 1982). By associating this convergent input these cells are thus able to monitor, coordinate and guide limb movement (Cohen et al. 1994) as well as determine the position of the body and objects in space.

Through the integrative and associative activities of the cell assemblies within area five, an interactional image of the body is maintained. In this manner, an individual is able to ascertain the positon of the body and the limbs at rest and in motion (Gross, et al. 1974). In part, this may be accomplished through comparisons with a more stable image of the body which is possibly maintained via the combined interactions of neurons in areas 3,1,2. That is a stable body image (or body image memories) are stored in these tissues. Hence, when the body has moved, this new information (received and processed in area 5) can be compared to the more stable trace (or memory maintained in the primary regions) so that the new position of the limbs and body can be ascertained. In this regard it could be argued that body-related memories are stored in the parietal lobe.

Nevertheless, to determine position, sensation per se is not sufficient. Rather, sensation must be combined with input regarding movement or positional change (Gandevia & Burke 1992). It is for this reason that in the absence of movement (and in the absence of visual cues, such as when one wakes up in the middle of the night) one usually cannot tell where or in what position their arms or legs may be in. However, with a slight movement we can immediately determine position.

PAIN: AREAS 5, 7, & THE SUPRAMARGINAL GYRUS

As noted, neurons in area 5, as well as those located in the insula, receive direct thalamic input from the ventral and posterior portion of VPL. The ventral portion in particular, however, in addition to somesthetic information, may also convey pain sensation to the parietal lobe. In fact, Penfield and Boldrey (1937) reported that electrical stimulation of the parietal lobe resulted in the sensation of pain, albeit about 1% of the time.

Some neurons located in area 5 and 7 of the parietal lobe also demonstrate pain sensitivity, with some are 7 neurons responding exclusively to thermal and nociceptive stimuli (Dong et al. 1994) and with area 5 presumably acting to localize the source of pain. Hence, in some instances, such as when the more inferior portion of area 5, 7 or the supramarginal gyrus (Broadmann's area 40) has been destroyed, patients may demonstrate a lack of emotional responsiveness to painful stimuli, become indifferent, develop an increased pain threshold, tolerate pain for an unusually lengthy time period and fail to respond even to painful threat (Berkley & Parmer, 1974; Biemond, 1956; Geschwind, 1965; Greenspan & Winfield 1992; Hyvarinen, 1982; Schilder, 1935) --particularly with right parietal destruction (Cubelli et al 1984). However, disturbance or lack of pain sensation has been noted to occur when lesions to either hemisphere (Hecaen & Albert, 1978).

Moreover, loss of sensation or an inability to react to pain may also occur from subcortical lesions, especially within the thalamus, and less often, with surgical destruction of the anterior cingulate--the so called center of "pain and misery." In this regard, there appears to be two major cerebral pain pathways, a subcortical medial pathway involving the thalamus and cingulate, and a neocortical pathway involving the parietal lobe.

At the neocortical level, although pain responsiveness may be diminished or absent following damage to these tissues, elementary sensation remains intact and the ability to differentiate, for example, between dull and sharp is retained. The deficit is usually bilateral.

[-INSERT FIGURE 9 ABOUT HERE-]

Some researchers have claimed that in order to lose pain sensitivity the lesion sometimes involves the frontal-parietal cortex (Hecaen & Albert, 1978). However, the supramarginal gyrus of the inferior parietal lobule (Geschwind, 1965; Hyvarinen, 1982; Schilder, 1935) and area 7 of the superior parietal lobule (Dong et al. 1994; Greenspan & Winfield 1992) are the most likely candidates for this condition --particularly in that a second somesthetic area is located here as well as yet another image of the human body (Penfield & Rasmussen, 1950).

In this regard, Schilder (1935), has argued that the loss of reaction to pain is due to disturbances in the image of the body. That is, the experience or threat of pain is no longer related to the body image. Geschwind, (1965), however, raises the possibility that this condition is due to disconnection from the limbic system (see Cavada & Goldman-Rakic 1989). If this were the case, somesthetic (painful) sensation would no longer be assigned emotional significance and would thus implicate the insular region of the parietal lobe, which also receives visceral as well as somesthetic information and funnels this data to the limbic system.

[-INSERT FIGURE 10 ABOUT HERE-]

In fact, this same insular-limbic pathway may serve to promote tactile memory; that is, via the funneling of complex somesthetic information to the hippocampus and amygdala. Conversely, it may be this same pathway which when abnormally activated or injured, may give rise to abnormal emotional significance being attributed to bodily sensations.

PAIN AND HYSTERIA

Whereas destruction of the inferior portions of areas 7, 5, and 40 may result in loss of pain sensation, when the injury is secondary to tumor or seizure activity patients may instead report experiencing pain (Davidson & Schick, 1935; Hernandez-Peon et al. 1963; Ruff, 1980; Wilkinson, 1973; York et al. 1979). In addition patients may experience sensory distortions that concern various body parts due to abnormal activation of the parietal neocortex.

For example, one 48 year old housewife complained of diffuse, poorly localized (albeit intense) pain in her left leg, which occurred in spasms that lasted minutes. She subsequently was found to have a large tumor in the right parietal area, which, when removed, alleviated all further attacks. Head and Holmes (1911) reported a patient who suffered brief attacks of "electric shock"-like pain that radiated from his foot to the trunk; a glioma in the right parietal area subsequently was discovered.

Sometimes the pain may be related to abnormal sexual or genital sensations. For example, one 9-year-old boy seizure activity in the right parietal area experienced spontaneous attacks of intense scrotal and testicular pain (York et al.1979). Ruff (1980) reports two cases who experienced paroxsymal episodes of spontaneous and painful orgasm, which was secondary to right parietal seizure activity. In one patient the episodes began with the sensation of clitoral warmth, engorgement of the breasts, tachycardia, etc., all of which rapidly escalated to a painful climax.

It is important to note, however, that although the predominant focus for paroxysmal pain is the right hemisphere, pain also has been reported to occur with tumors or seizures activity that involves the left parietal region (Bhaskar, 1987; McFie & Zangwill, 1960).

Unfortunately, when the patient's symptoms are not considered from a neurological perspective, their complaints with regard to pain may be viewed as psychogenic in origin. This is because the sensation of pain, stiffness, engorgement, is, indeed, entirely "in their head" and based on distorted neurological perceptual functioning. Physical exam may reveal nothing wrong with the seemingly affected limb or organ. Thus such patients may be viewed as hysterical or hypochondriacle, particularly in that right hemisphere damage also disrupts emotional functioning.

THE RIGHT & LEFT PARIETAL LOBE: LESIONS & LATERALITY

ATTENTION & VISUAL SPACE

Lesions involving the superior, as well as the inferior parietal lobule (of which area 7 is part) and the parietal-occipital junction can greatly disturb the ability to make eye movements, maintain or shift visual attention, visually follow moving objects, and in the extreme result in oculomotor paralysis (Hecaen & De Ajuriaguerra, 1954; Previc 1990). Right parietal lesions are associated with deficiencies involving depth perception and stereopsis, including the abilIty to determine location, distance, spatial orientation and object size (Benton & Hecaen, 1970; Ratcliff & Davies-Jones, 1972). Visual constructional abilities may also be compromised (see Cowey, 1981; Critchley, 1953) and many patients suffer from visual-spatial disorientation and appear clumsy.

Individuals with right parietal lesions show defective performance on line orientation tasks (Warrington & Rabin, 1970; Benton et al. 1975), maze learning (Newcombe & Russell, 1969), the ability to discriminate between unfamiliar faces (Milner, 1968), or to select from the visual envrionment stimuli which are of importance is also a consequence of right parietal lesions (Critchley, 1953), whereas those with right parietal-occipital damage are deficient on tasks requiring detection of imbedded figures (Russo & Vignolo, 1967).

Others may also have severe problems with dressing (e.g. dressing apraxia) and may become easily lost or disoriented even in their own homes. One patient I examined with a gun shot wound involving predominantly the right superior posterior parietal area was unable to find his way to and from his hospital room (although he had been an inpatient for over 3 months) and on several occasions had difficulty finding his way out of the bathroom. Indeed, in one instance he was discovered feeling his way along the walls in his attempt to find the door.

Commonly right parietal injuries can result in a complete neglect of the left half of visual space. By contrast, left parietal injuries result in only minimal right sided neglect. Again, this is because the right parietal lobe not only attends to both halves of the body, but both halves of visual space (Joseph, 1986ab, 1988a).

CONSTRUCTIONAL AND SPATIAL PERCEPTUAL SKILLS

Based on studies of brain injured, neurosurgical (e.g., temporal lobectomy, split-brain), and normal populations, the right cerebral hemisphere has been found to be dominant over the left in the analysis of geometric and visual-space, the perception of depth, distance, direction, shape, orientation, position, perspective, and figure-ground, the detection of complex and hidden figures, the performance of visual closure, and the ability to infer the total stimulus configuration from incomplete information, route finding and maze learning, localizing targets in space, the performance of reversible operations, stereopsis, and the determination of the directional orientation of the body as well as body-part positional relationships (Benton 1993; Butters & Barton, 1970; Carmon & Bechtoldt, 1969; DeRenzi & Scotti, 1969; DeRenzi et al. 1969; Ettlinger, 1960; Fontenot, 1973; Franco & Sperry, 1977; Fried et al. 1982; Hannay et al., 1987; Kimura, 1966; 1969, 1993; Landis et al. 1986; Lansdell, 1968, 1970; Levy, 1974; Milner, 1968; Nebes, 1971; Sperry, 1982). Hence, if the right hemisphere is injured, visual-spatial perceptual functioning is negatively impacted.

[-INSERT FIGURES 10 ABOUT HERE-]

In addition, the isolated right hemisphere has been found to be superior in "fitting designs into larger matrices, judging whole circle size from a small arc, discriminating and recalling nondescript shapes, making mental spatial transformations, sorting block sizes and shapes into categories, perceiving wholes from a collection of parts, and the intuitive perception and apprehension of geometric principles" (Sperry, 1982, p.1225).

Thus, it is the right hemisphere which enables us to find our way in space without getting lost, to walk and run without tripping and falling, to throw and catch a football with accuracy, to drive a car without bumping into things, to draw conclusions based on partial information, and to see the forest when looking at the trees. The right is also superior to the left in analyzing manipulo-spatial problems, drawing and copying simple and complex geometric-like figures and performing constructional tasks, block designs and puzzles (Benson & Barton, 1970; Black & Strub 1976; Critchley, 1953; DeRenzi, 1982; Gardner, 1975; Hecaen & Albert, 1978; Hier et al. 1983; Kertesz, 1983b; Levy, 1974; Luria, 1973, 1980; Piercy et al. 1960). It is for these and other reasons that the right brain is often viewed as the artistic half of the cerebrum.

The right hemisphere is also dominant over the left in regard to localizing and thus referencing the position of an object in space (Cook et al. 1994; Nunn et al., 1999; Ploner et al., 1999), as well as in aiming and closed loop throwing accuracy (Guiard et al. 1983; Haaland & Harrington, 1990). Of course, most individuals use the right hand to throw (as well as draw). Presumably the right hemisphere is able to guide right limb and related axial movements (Rapcsak et al. 1993) via bilateral SMA and parietal lobe innervation of the basal ganglia and lower motor neurons (see chapters 16, 19).

CONSTRUCTIONAL APRAXIA

Constructional apraxia is by no means a unitary disorder (Benton, 1969; Benson & Barton, 1970) and can may be expressed in a number of ways. On a drawing or copying task this may include the addition of unncessary/non-existant details or parts, misalignment or inattention to details, disruptions of the horizontal and verticle axis with reversals or slight rotations in reproduction, and scattering of parts. For example, in performing the Block Design subtest from the WAIS-R, the patient may correctly reproduce the model but angle it incorrectly. In drawing or copying figures, the patient may neglect the left half, draw over the model, and misalign details.

Moreover, although constructional deficits are more severe after right hemisphere damage (Arrigoni & DeRenzi, 1964; Black & Strub, 1976; Benson & Barton, 1970; Critchley, 1953; Hier et al., 1983; Joseph, 1988a; Kimura 1993; Piercy et al. 1960), disturbances involving constructional and manipulo-spatial functioning can occur with lesions to either half of the brain (Arrigoni & DeRenzi, 1964; Mehta et al., 1987; Piercy et al., 1960). Hence, depending on the laterality, as well as the extent and site of the lesion, the deficit may also take different forms. For example, following posterior reight cerebral lesions, rather than apraxic, the patient is spatially-agnosic, i.e. suffering from constructional agnosia and a failure to perceive and recognize visual-spatial and object interrelationships. In other cases, such as following left cerebral injury, the disturbance may be secondary to a loss of control over motor programming (Kimura 1993; Warrington et al., 1966; Warrington, 1969).

Although visual motor deficits can result from lesions in either hemisphere (Arrigoni & DeRenzi, 1964; Piercy et al., 1960; Kimura 1993), visual-perceptual disturbances are more likely to result from right hemisphere damage. In contrast, lesions to the left half of the brain may leave the perceptual aspects undisturbed whereas visual motor functioning and selective organization may be compromised (Kim et al. 1984; Mehta et al., 1987; Poeck et al. 1973). As such the patient is likely to recognize that errors have been made.

In general, the size and sometimes the location of the lesion within the right hemisphere has little or no correlation with the extent of the visual-spatial or constructional deficits demonstrated, although right parietal lesions tend to be worst of all. With right parietal involvement patients tend to have trouble with the general shape and overall organization, the correct alignment and closure of details, and there may be a variable tendency to ignore the left half of the figure or to not fully attend to all details. Moreover the ability to perceive (or care) that errors have been made is usually compromised.

Conversely, constructional disturbances associated with left hemisphere damage are positively correlated with lesion size, and left anterior lesions are worse than left posterior (Benson & Barton, 1970; Black & Bernard, 1984; Black & Strub, 1976; Kimura 1993; Lansdell, 1970). This is because the capacity to control and program the motor system has been compromised. The larger the lesion, the more extensive the deficit.

Moreover, because the left hemisphere is concerned with the analysis of parts or details and engages in temporal- sequential motor manipulations, lesions result in oversimplification and a lack of detail although the general outline or shape may be retained (Gardner, 1975, Levy, 1974). However, in some cases, when drawing, there may be a tendency to more greatly distort the right half of the figure with some preservation of left sided details.

MUSIC, MATH AND GEOMETRIC SPACE

Pythagoras, the great Greek mathematician, argued almost 2,000 years ago that music was numerical, the expression of number in sound (Durant 1939; McClain 1978). In fact, long before the advent of digital recordings, the Babylonians and Hindus, and then Pythagoras and his followers translated music into number and geometric proportions (Durant 1939). For example, by dividing a vibrating string into various ratios they discovered that several very pleasing musical intervals could be produced. Hence, the ratio 1:2 was found to yield an octave, 2:3 a fifth, and 3:4 a fourth, 4:5 a major third, and 5:6 a minor third (McClain 1978). The harmonic system utilized in the nineteenth century by various composers was based on these same ratios. Indeed, Bartok utilized these ratios in his musical compositions.

These same musical ratios, the Pythagorians discovered, also were found to have the capability of reproducing themselves. That is, the ratio can reproduce itself within itself and form a unique geometrical configuration which Pythagoras and the ancient Greeks referred as the the "golden ratio" or "golden rectangle." The gold rectangle was postulated to have devine inspirational origins. Indeed, music itself was thought by early man to be magical, whereas musicians were believed by the ancient Greeks to be "prophets favored by the Gods" (Worner, 1973).

[-INSERT FIGURES 8, 9, ABOUT HERE-]

This same golden rectangle is found in nature, i.e., the chambered nautilus shell, the shell of a snail, and in the ear --the cochleus. The geometric proportions of the golden rectangle were also employed in designing the Parthenon in Athens, and by Ptolemy in developing the "tonal calender" and the "tonal Zodiac" (McCain, 1978) -the scale of ratios "bent round in a circle."

In fact, the first cosmologies, such as those developed by the ancient Egyptians, Hindus, Babylonians, and Greeks, were based on musical ratios (Durant, 1939; McClain, 1978). Pythagorus and Plato applied these same "musical proportions" to their theory of numbers, planetary motion, and to the science of stereometry --the gauging of solids (McClain, 1978). Indeed, Pythagorus attempted to deduce the size, speed, distance, and orbit of the planets based on musical ratios as well as estimates of the sounds generated (e.g., pitch and harmony) by their movement through space, i.e. "the music of the spheres" (Durant, 1939).

Interestingly, the famous mathematician and physicist Johannes Kepler in describing his laws of planetary motion also referred to them as based on the "music of the spheres." Thus music seems to have certain geometric properties, such as are expressed via the ratio. Indeed, Pythagrous, the "father" of arithmetic, geometry, and trigonometry, believed music to be geometric.

"Words and language,whether written or spoken,do not seem to lay any part in my thought processes. The psychological entities that serve as building blocks for my thought are certain signs or images, more or less clear, that I can reproduce at will." A. Einstein

As we know, geometry is employed in the measurement of land, the demarcation of boundaries, and, thus, in the analysis of space, shape, points, lines, angles, surfaces, and configuration.

In nature, one form of musical expression, that is, the songs of most birds, also is produced for geometric purposes. That is, a bird does not "sing for joy," but to signal others of impending threat, to attract mates, to indicate direction and location, to stake out territory, and to warn away others who may attempt to intrude on his space (Catchpole, 1979; Hartshorne, 1973).

If we may assume that long before man sang his first song, the first songs and musical compositions were created by our fine feathered friends (sounds that inspired mimicry by woman and man) then it appears that musical production was first and foremost emotional and motivational, and directly related to the geometry of space; the demarcation of one's territory. Emotion and geometry are characteristics that music still retains today, they are linked neurologically. This is also why training in music can improve visual-spatial (as well as mathematical) skills and vice-versa.

SEX DIFFERENCES IN SPATIAL ABILITY Right cerebral visual-spatial and geometric

superiorities constitute skills that would enable an ancient hunter to visually track, throw a spear and dispatch various prey while maintaining a keen awareness of all else occurring within the environment. For most of human (and probably chimpanzee and baboon) history, males have typically been the hunters, whereas females (including female chimps) spend much more time gathering.

Not surprisingly, males are far superior to females in regard to visual-spatial functioning and analysis (Broverman, et al. 1968; Dawson et al. 1978; Harris, 1978; Joseph, 1999e; Kimura, 1993; Levy and Heller, 1992). This includes a male superiority in the recall and detection of geometric shapes, detecting figures that are hidden and embedded in an array of other stimuli, constructing 3-dimensional figures from 2-dimensional patterns, visually rotating or recognizing the number of objects in a 3-dimensional array, playing and winning at chess (which requires superior spatial abilities). Males also possess a superior geometric awareness, directional sense and greater geographic knowledge, are better at solving tactual and visual mazes, and are far superior to females in aiming, throwing, and tracking such as in coordinating one's movements in relationship to a moving target (reviewed in Broverman, et al. 1968; Harris, 1978; Joseph, 1999e; Kimura, 1993; Levy and Heller, 1992). In contrast, only about 25% of females in general exceed the average performance of males on tests of such abilities (Harris, 1978).

Moreover, some of these differences are present during childhood and have been demonstrated in other species (Dawson et al. 1978; Harris, 1978; Levy & Heller, 1992; Joseph, 1979; Joseph and Gallagher, 1982; Joseph et al. 1978). For example, male rats consistently demonstrate superior visual-spatial skills as compared to females (Joseph, 1979, Joseph & Gallagher, 1982; Joseph et al. 1978). In fact, these sex difference are ameliorated only when females are reared in a complex, socially and environmentally enriched environment and when males are placed in a restricted and impoverished environment; in which case males and females perform similarly (Joseph & Gallagher 1982). When environments are similar (enriched or deprived) males outperform females. Hence, environmental influences do not cause these sex differences which are obviously innate.

In large part, these sex differences in spatial ability are clearly a function of the presence or absence of testosterone during human fetal development (Joseph et al. 1978), as well as the differential activities of males vs females for much of human history; i.e. hunting vs gathering. Hence, over the course of evolution, natural males vs female superiorities have been enhanced.

However, in this regard, just as females appear to have more brain space devoted to language functions, it also appears that males have more neocortical space devoted to spatial-perceptual and related expressive functions (Joseph, 1993).

VISUAL-PERCEPTUAL ABNORMALITIES

When the male or female right hemisphere is damaged, most aspects of visual-spatial and perceptual functioning can become altered, including nonlingusitic memory. For example, right temporal lobe damage impairs memory for abstract designs, tonal melodies, objects, positions, and visual mazes (Kimura, 1963; Milner, 1968; Nunn et al., 1999). Deficits in left sided attention, the ability to make judgments which involve visual-figural relationships, in detecting hidden, embedded, and overlapping nonsense figures, recognizing or recalling recurring shapes, and disturbances in the capacity to perceive spatial wholes and achieving visual closure can result (Bartolomeo et al. 1994; Benton, 1993; Binder et al. 1992; DeRenzi, 1982; DeRenzi et al., 1969; Ettlinger, 1960; Gardner, 1975; Kimura, 1963, 1966, 1969; Landis et al., 1986; Lansdell, 1968; 1970; Levy, 1974).

Such individuals may misplace things, have difficulty with balance and stumble and bump into walls and furniture, become easily lost, confused and disoriented while they are walking or driving; and have difficulty following directions or even putting on their clothes. Indeed such patients easily can get lost while they are walking down familiar streets and even in their own homes (Benton, 1993; DeRenzi, 1982; DeRenzi et al., 1969; Ettlinger, 1960; Gardner, 1975; Landis et al., 1986; Lansdell, 1968a; 1970; Levy, 1974). Right brain damage also can also result in disorientation, problems in assuming different perspectives, and even with dressing (Hecaen, 1962; Hier et al., 1983).

In some instances, the deficit can be quite subtle and circumscribed. For example, one patients only complaint (3 months after he suffered a circumscribed blunt head injury that resulted in a subdural hemotoma over the right posterior temporal-parietal area) was that his golf game had deterioarted significantly and he was no longer as accurate when throwing wads of paper into the trash can in his office. Formal testing also indicated mild constructional and manipulo-spatial disturbances, with most other capacities in the high average to superior range.

DRAWING AND CONSTRUCTIONAL DEFICITS

The left hemisphere also contributes to visual-spatial processing and expression such that when damaged drawing ability can be affected (Kimura, 1993), albeit in a manner different from that of the right (Mehta et al. 1987). For example, because the left is concerned with the analysis of parts or details lesions result in sequencing errors, oversimplification and a lack of detail in drawings such that details may be ignored, although the general outline or shape may be retained (Bradshaw & Mattingly, 1995; Gardner, 1975; Joseph, 1988a; Kimura, 1993; Levy, 1974).

In contrast, the right cerebrum is more involved in the overall perceptual analysis of visual and object interrelations including visual closure and gestalt formation. Thus, patients with right cerebral injuries have trouble with general shape and organization, although certain details may be drawn correctly. Drawings may also be grossly distorted and/or characterized by left sided neglect.

Right sided damage also can affect writing. When patients are asked to write cursively, writing samples may display problems with visual closure, as well as excessive segmentation due to left hemisphere release (Joseph, 1988a). That is, cursively the word "recognition" may be written "re cog n i tion," or letters such as "o" may be only partly formed.

Constructional deficits are more severe after right hemisphere damage (Arrigoni & DeRenzi, 1964; Black & Strub, 1976; Benson & Barton, 1970; Bradshaw & Mattingly, 1995; Critchley, 1953; Hier et al., 1983; Piercy et al., 1960). However, lesions to either hemisphere can create disturbances in constructional and manipulo-spatial functioning -including performance on the WAIS Block Design and Object Assembly subtests (Arrigoni & DeRenzi, 1964; Cubelli et al. 1991; Kimura, 1993; Mehta et al., 1987; Piercy et al., 1960).

If the left hemisphere is damaged, performance may be impaired due to motor programming errors and/or an inability to transform the percept into a motor action with preservation of good spatial-perceptual functioning (Warrington et al., 1966); in which case errors may be recognized by the patient. With right cerebral injuries, visual-spatial perceptual functioning becomes distorted (although motor activities per se are preserved) and the patient may not realize they have made an error (Hecaen & Assal, 1970).

[-INSERT FIGURE 11 ABOUT HERE-]

Thus, visual motor deficits can result from lesions in either hemisphere (Arrigoni & DeRenzi, 1964; Bartolomeo et al. 1994; Kimura, 1993; Piercy et al., 1960), though visual-perceptual disturbances are more likely to result from right hemisphere damage. Lesions to the left half of the brain may leave the perceptual aspects undisturbed whereas visual motor functioning and selective organization may be compromised (Kim et al. 1984; Mehta et al., 1987; Poeck et al. 1973; Teuber & Weinstein, 1956) and attentional functioning may be disturbed (Bartolomeo et al. 1994; Cubelli et al. 1991).

In general, the size and sometimes the location of the lesion within the right hemisphere have little or no correlation with the extent of the visual-spatial or constructional deficits demonstrated (Kimura, 1993), although right posterior lesions tend to be worst of all. For example, in a restrospective study of 656 patients with unilateral lesions that employed a short form of the WAIS, Warrington, James and Maciejewski (1986), found that those with right posterior (vs. anterior or left hemisphere) damage had the lowest Performance IQs as well as difficulty performing the block design and picture arrangment subtests.

Conversely, visual-perceptual disturbances associated with left hemisphere damage are positively correlated with lesion size; and left anterior lesions are worse than left posterior (Benson & Barton, 1970; Black & Bernard, 1984; Black & Strub, 1976; Lansdell, 1970). The larger the lesion, the more extensive the deficit. Kimura (1993), however, argues that males are more likely to demonstrate these disorders with left posterior lesions, whereas in females the lesion tends to be more anterior.

As pertaining to WAIS PIQ-VIQ differences, based on an extensive review of the literature, Bornstein and Matarazzo (1982) have have confirmed what is now generally well known; i.e. that those with left hemisphere lesions have lower VIQs, whereas those with right sided damage have lower mean PIQs. Reading and Math.

Because of its importance in visual orientation, the right hemisphere also participates in math and reading. Visual-spatial orientation is important when performing a variety of math problems, such as in correctly aligning numbers when adding multiple digits. Conversely, right sided lesions may cause the patient to neglect the left half of digit pairs while adding or subtracting (Hecaen & Albert, 1978; Luria, 1980).

Moreover, some aspects of math, such as what Dehaene and colleagues (1999. p. 970), refer to as "approximate" arithmetic, is language independent and "relies on a sense of numerical magnitudes, and recruits bilateral areas of the parietal lobes involved in visuo-spatial processing." Hence, right parietal lesions can disrupt this more intuitive aspect of mathematical reasoning.

Moreover, via the analysis of position, orientation, etc., the right cerebrum enables a human to read the words on this page without losing their place and jumping half-hazardly from line to line. Conversely, when damaged, patients may fail to attend to the left half of written words, or even the left half of the page (Critchely, 1953; Gainotti, et al. 1972, 1986).

Because the right half of the cerebrum can make conclusions based on partial information, e.g. closure and gestalt formation, humans need not read every or all of each word in order to know what they have read. For example, when presented with incomplete words or perceptually degraded written stimuli, there is an initial right hemisphere superiority in processing (Hellige & Webster, 1979); i.e. visual closure, which enables an individual to fill-in these gaps and thus comprehend. Of course, sometimes people draw the wrong conclusions from incomplete perception (e.g. reading "word power" as "world power"), a problem that can become exaggerated if the right half of the brain has been damaged.

In addition, when the visual-figural characteristics of written language are emphasized, such as when large gothic scriptis employed (e.g., in Tachistoscopic studies) the right hemisphere is dominant (Bryden & Allard, 1976; Wagner & Harris, 1994). Similarly, when presented with unfamiliar written words, or a foreign alphabet, there is an initial right hemisphere perceptual dominance (Silverberg et al. 1979), apparently as the left hemisphere does not immediately recognize these stimuli as "words," whereas the right hemisphere attends to their shape and form.

Indeed, based on an extensive analysis of the evolution of written language , there is some evidence to suggestan initial right hemisphere dominance, particularly in that much of what was written was at first depicted in a pictorial, gestalt-like fashion (see chapter 6). The use of images preceded the use of signs (Campbell 1988; Chiera, 1966; Joseph 1993; Jung, 1964).

INATTENTION AND VISUAL-SPATIAL NEGLECT

Unilateral inattention and neglect are associated most commonly with right hemisphere (parietal, frontal, thalamic, basal ganglia) damage, particularly following lesions located in the temporal-parietal and occipital junction (Bartolomeo et al. 1994; Binder et al. 1992; Bisiach et al.1983; Bisiach & Luzzatti, 1978; Bradshaw & Mattingly, 1995; Brain, 1941; Calvanio et al. 1987; Critchely,. 1953; De Renzi, 1982; Ferro, Kertesz & Black, 1987; Gainotti, et. al.1986; Heilman, 1993; Heilman et al. 1983; Joseph, 1986a; Motomura et al. 1986; Nielsen, 1937; M. Roth, 1949; N. Roth, 1944; Sterzi et al., 1993; Watson et al. 1981). Such patients initially may fail to respond, recall, or perceive left-sided auditory, visual, or tactile stimulation, fail to comb, wash, or dress the left half of their head, face, and body, only eat food on the right half of their plate, write only on the right half of a paper, fail to read the left half of words or sentences (e.g., if presented with "toothbrush" they may see only the word "brush"), or on drawing tasks, distort, leave out details, or fail to draw the left half of various figures, e.g., a clock or daisy (Binder et al. 1992; Bisiach et al., 1983; Calvanio et al., 1987; Critchley, 1953; DeRenzi, 1982; Gainotti et al.,1972, 1986; Hecaen & Albert, 1978; Umilta 1995; Young et al. 1992). Moreover, they show a greater degree of hemiplegia and hemianesthesia as compared to left hemisphere lesions (Sterzi et al., 1993).

When shown their paralyzed or neglected left arm or leg, such patients may deny that it is their own and claim that it belongs to the doctor or a patient in the next room. Indeed, "patients with severe unilateral neglect behave as if a whole system of beliefs had vanished, as if one half of the inner model of the environment were simply deleted from their mind (Bisiach et al. 1983, p. 35). In the less extreme cases, patients may seem inattentive such that when their attention is directed to the left half of the environment, they are able to respond appropriately (see Jeannerod, 1987; and Umilta 1995, for a detailed review).

[-INSERT FIGURES 12, & 13 ABOUT HERE-]

Imaginal and spatial-postional memory functioning also are disrupted (Nunn et al., 1999) such that patients may fail to attend to the left half of images recalled from memory. For example, Bisiach and Luzzatti (1978), found that when right brain damaged patients were asked to recall and describe a familiar scene from different perspectives, regardless of perspective (e.g. imagining a street from one direction and then from another) patients consistently failed to report details that fell to their left--although the same details were recalled when imagined from the opposite direction, their right. Bisiach and Luzzatti (1978) suggest that visual images and scenes may be split into two images when conjured up, such that the right hemisphere images the left half of space and the left brain the right half of space. Similar results were presented by Meador, Loring, Bowers, and Heilman, (1987).

Thus right cerebral injuries can result in visual-spatial as well as (imaginal) representational neglect. In some severe cases, patients may demonstrate both forms, whereas in others visual-spatial (but not representational) neglect may be found in isolation (Bartolomeo et al. 1994).

Neglect also can be influenced by the task demands (Bartolomeo et al. 1994; Binder et al 1992; Starkstein et al. 1993; Umilta 1995) and may be differentially expressed in the horizontal and vertical spatial dimension and in near vs far pepipersonal space (Mennemeir et al. 1992). For example, some patients may demonstrate neglect in the visual vs tactile modality (Umilta 1995), whereas yet others may adequately draw simple figures, but fail to correctly place numerals in the right half of space when drawing a clock.

Moreover, some authors have argued that letter cancellation tests appear to be more sensitive than line bisection tasks when testing for (right cerebral) neglect (Binder et al. 1992). Moreover, with the possible exception of letter cancellation, when the task is normally performed best by the damaged hemisphere (that is, before it was damaged) the neglect may be more pronounced (Leicester et al. 1969).

Thus a patient with a left cerebral injury may not respond to a verbal question or command, or they may tend to ignore objects or written material that falls to their extreme right. Hence, left brain damaged patients also may show unilateral inattention or neglect (Albert, 1973; Bartolomeo et al. 1994; Cubelli et al. 1991; Denny-Brown et al. 1952; Gainotti et al., 1986), albeit in a less severe form.

DISTURBANCS OF THE BODY IMAGE

In addition to nonlinguistic, prosodic, melodic, emotional and visual-spatial dominance, the right cerebrum has been shown to be superior to the left in processing various forms of somesthetic and tactile-spatial- positional information, including geometric, tactile-form and Braille-like pattern recognition (Bradshaw et al. 1982; Carmon & Benton, 1969; Corkin, Milner, & Rasmussen, 1970; Desmedt, 1977; Dodds, 1978; Fontenot & Benton, 1971; Franco & Sperry, 1977; Hatta, 1978a; Hermelin & O'Connor, 1971; Hom & Reitan, 1982; Pardo et al. 1991; E. Weinstein & Sersen, 1961).

The right cerebrum is also dominant for two point discrimination (S. Weinstein, 1978) pressure sensitivity (Semmes et al. 1960; S. Weinstein, 1978; E. Weinstein & Sersen, 1961) and processing tactual-directional information (Carmon & Benton, 1969; Fontenot & Benton, 1971). The right hemisphere may be more involved than the left in the perception of somesthetically mediated pain (Cubelli et al. 1984; Haslam, 1970; Murray & Hagan, 1973).

In addition, unlike the left, the right hemisphere is responsive to tactual stimuli which impinge on either side of the body (Desmedt, 1977; Pardo et al. 1991). Indeed, a somesthetic image of the entire body appears to be maintained by the parietal lobe of the right half of the brain (Joseph, 1988a); and not just a body image, but memories of the body, the left half in particular.

[-INSERT FIGURE 14 ABOUT HERE-]

When the right hemisphere is damaged, somesthetic functioning can become grossly abnormal, and patients may experience peculiar disturbances which involve the body image (Critchley, 1953; Gerstmann, 1942; Gold et al. 1994; Hillbom, 1960; Joseph, 1986a; Miller, 1984; Nathanson et al. 1952; M. Roth, 1949; N. Roth, 1944; Sandifer, 1946; E. Weinstein & Kahn, 1950, 1952). These patients may fail to perceive stimuli applied to the left side; wash, dress, or groom only the right side of the body; confuse body-positional and spatial relationships; misperceive left sided stimulation as occurring on the right; fail to realize that their extremities or other body organs are in some manner compromised; and/or literally deny that their left arm or leg is truly their own.

When confronted by their unused or paralyzed extremities, such patients may claim that they belong to the doctor or a person in the next room or, conversely, seem indifferent to their condition and/or claim that their paralyzed limbs are normal --even when unable to comply with requests to move them.

"When asked why she could not move her hand she replied, 'somebody has ahold of it.' Another patient, when asked if anything was wrong with her hand said, 'I think it's the weather. I could warm it up and it would be alright.' One woman, when asked whether she could walk said, 'I could walk at home, but not here. It's slippery here." Another patient, when asked why he couldn't raise his arm said, 'I have a shirt on'" (Nathanson et al., 1952; p. 383).

Neglect & Denial: Emotional Reactions.

Many patients also appear indifferent and/or make inappropriate emotional remarks about their disability. Given right cerebral dominance for emotion, perhaps not surprisingly, many patients may appear and behave inappropriately and may even laugh and joked about being paralyzed.

In an extensive examination of these disturbances, E. Weinstein and Kahn (1950) found that of 22 patients (only 3 of whom were thought to have predominantly left hemisphere dysfunction), 15 were euphoric and manifested an air of serenity or bland unconcern about their condition despite the fact that they were suffering from disorders such as hemiplegia, blindness, loss of memory, and incontinence. Ten of these individuals also behaved in a labile or transiently paranoid fashion.

Right cerebral lesions have been reported to slow the appearance of phantom limbs on either side of the body and can result in the loss of phantom limb pain (S. Weinstein, 1978). In contrast, left sided lesions seem to have little effect. In general, like neglect and inattention, lesions which result in body image disturbances tend to involve the right parietal or right frontal lobe (Bradshaw & Mattingly, 1995; Critchley, 1953; Joseph, 1986a, 1988a; Stuss & Benson, 1986). In this regard, the fact that lesions of the left hemisphere rarely result in neglect or body image disturbances suggests that the right hemisphere maintains a bilateral representation, and memories of the body, whereas the left cerebrum maintains a unilateral representation and a memory of only the right half of the body -memories which are stored in the parietal lobe, a portion of which evolved from the hippocampus which is also concerned with memory, including memory of the body in space (chapters 13, 14). This bilateral representation of the body image vs the unilateral representation maintained by the left hemisphere, also explain the greater degree of hemiplegia and hemianesthesia which is seen after right vs left parietal lesions (Sterzi et al., 1993).

[-INSERT FIGURE 15 ABOUT HERE-]

Hence, when the left hemisphere is damaged, the right hemisphere continues to monitor (and remember) both halves of the body and there is little or no neglect --an impression supported by findings which indicate that the right hemisphere electrophysiologically responds to stimuli that impinge on either side of the body, whereas the left hemisphere predominantly responds only to right sided stimulation (Desmedt, 1977; Pardo et al. 1991).

PAIN AND HYSTERIA

In addition to body image distortions parietal lobe injuries (particularly when secondary to tumor or seizure activity) also can give rise to sensory misperceptions such as pain (Davidson & Schick, 1935; Hernandez-Peon et al. 1963; Ruff, 1980; Wilkinson, 1973; York et al. 1979). That is, in the less extreme cases, rather than failing to perceive (i.e. neglecting ) the left half of the body, patients may experience sensory distortions that concern various body parts due to abnormal activation of the right hemisphere and parietal lobe.

For example, one 48 year old housewife complained of diffuse, poorly localized (albeit intense) pain in her left leg, which occurred in spasms that lasted minutes. She subsequently was found to have a large tumor in the right parietal area, which, when removed, alleviated all further attacks. Head and Holmes (1911) reported a patient who suffered brief attacks of "electric shock"-like pain that radiated from his foot to the trunk; a glioma in the right parietal area subsequently was discovered. McFie and Zangwill (1960) reported an individual who began to experience intense, extreme pain in a phantom arm after a right posterior stroke.

In another instance reported by York et al., (1979), a 9-year-old boy experienced spontaneous attacks of intense scrotal and testicular pain and was found to have seizure activity in the right parietal area. Ruff (1980) reports two cases who experienced paroxsymal episodes of spontaneous and painful orgasm, which was secondary to right parietal seizure activity. In one patient the episodes began with the sensation of clitoral warmth, engorgement of the breasts, tachycardia, etc., all of which rapidly escalated to a painful climax. Interestingly, in the normal intact individual, orgasm is associated with electrohysiological arousal predominantly within the right hemisphere (H. Cohen et al. 1976).

It is important to note, however, that although the predominant focus for paroxysmal pain is the right hemisphere, pain also has been reported to occur with tumors or seizures activity that involves the left parietal region (Bhaskar, 1987; McFie & Zangwill, 1960).

Unfortunately, when the patient's symptoms are not considered from a neurological perspective, their complaints with regard to pain may be viewed as psychogenic in origin. This is because the sensation of pain, stiffness, engorgement, is, indeed, entirely "in their head" and based on distorted perceptual functioning at the level of the neocortex. Physical exam may reveal nothing wrong with the seemingly affected limb or organ -unless neocortical damage is extensive, in which case the patient may display paresis, sensory loss, etc. Even under these latter condtions such patients may be viewed as hysterical or hypochondriacle, particularly in that right hemisphere damage also disrupts emotional functioning. For example, in one case a woman patient suspected of hysteria subsquently was found to have a right frontal-parietal and mid-temporal cyst (Joseph, 1988a). This same individual had difficulty recognizing or mimicking emotional and environmental sounds.

It is noteworthy that individuals suspected of suffering from hysteria are two to four times more likely to experience pain and other distortions on the left side of the body (Axelrod et al. 1980; Galin, Diamond & Braff 1977; Ley 1980; D. Stern 1977); findings which in turn, suggest that the source of the hysteria may be a damaged right hemisphere.

This supposition is supported further by the raw MMPI data provided by Gasparrini, Satz, Heilman, and Cooldige (1978) in their study of differential effects of right vs. left hemisphere damage on emotional functioning. That is, whereas depression (elevated MMPI scale 2) is more likely subsequent to left cerebral damage, a pattern suggestive of hysteria and conversion reactions (elevations on scales 1 and 3, reductions on scale 2; i.e., the Conversion "V") are more likely subsequent to right hemispheric lesions.

The findings of Gasparrini et al. (1978) were replicated based on a restrospective case analysis of individuals with long standing right vs. left hemisphere injury (verified by neuropsychological exam coupled with CT-scan and/or EEG). In this study the MMPI Conversion V profile was found to be associated signficantly and almost exclusively with right hemisphere injuries (among males only), whereas elevated scale 2 was associated with those with left sided damage (Joseph, unpublished data). However, not every patient demonstrated this pattern.

[-INSERT FIGURE XX (MMPI Figure from Chapter 31) ABOUT HERE-]

At least one investigator, however, reporting on psychiatric patients has attributed hysteria to left cerebral damage (Flor-Henry 1983). In part this may be a function of the statistical permutations utilized in analyzing his data. However, this also may reflect the nature of the population studied (i.e., psychiatric rather than neurological) and, thus, the differential effect of long-standing drug treatments and biochemical and congenitial disturbances vs. recently acquired neuroanatomical lesions.

DELUSIONAL DENIAL

Frequently, patients with right parietal lesions, when confronted with their unused or immobile limbs may (at least initially) deny that it belongs to them or swear there is nothing wrong (Gold et al. 1994; Heilman 1991; Joseph, 1986a, 1988a). More often, however, they tend to ignore their left half. In some cases, however, patients may perceive the left half of their body but refer to it using ego-alien language, such as "my little sister", "my better half", "my friend Tommy" , "my brother-in-law", "spirits", etc.

For example, Gerstmann (1942) describes a patient with left-sided hemiplegia who "did not realized and on being questioned denied, that she was paralyzed on the left side of the body, did not recognize her left limbs as her own, ignored them as if they had not existed, and entertained confabulatory and delusional ideas in regard to her left extremities. She said another person was in bed with her, a little Negro girl, whose arm had slipped into the patient's sleeve" (p. 894). Another declared, (speaking of her left limbs), "That's an old man. He stays in bed all the time."

One such patient engaged in peculiar erotic behavior with his "absent" left limbs which he believed belonged to a woman. A patient described by Bisiach and Berti (1987, p. 185) "would become perplexed and silent whenever the conversation touch upon the left half of his body; even attempts to evoke memories of it were unsuccessful". Moreover, although "acknowledging that all people have a right and a left side, he could not apply the notion to himself. He would affirm that a woman was lying on his left side; he would utter witty remarks about this and sometimes caress his left arm".

Some patients may develop a dislike for their left limbs, try to throw them away, become agitated when they are referred to, entertain persecutory delusions regarding them, and even complain of of strange people sleeping in their beds due to their experience of bumping into their left limbs during the night (Bisiach & Berti, 1987; Critchley, 1953; Gerstmann, 1942). One patient complained that the person tried to push her out of the bed and then insisted that if it happened again she would sue the hospital. Another complained about "a hospital that makes people sleep together". A female patient expressed not only anger but concern least her husband should find out; she was convinced it was a man in her bed.

DISCONNECTION, CONFABULATION & GAP FILLING

In some respects it seems quiet puzzling that individuals with right parietal injuries may deny what is visually apparent and what they should easily be able to remember, i.e. the presence of the left half of their body. However, it is possible that when the language dominant left hemisphere denies ownerhip of the left extremity it is in fact telling the truth. That is, the left arm belongs to the right not the left hemisphere. Indeed, in that the parietal lobe is in part an evolutionary derivative of the hippocampus (which also contains neurons that code for the position of the body and objects in space), not just a body image and the body in space, but the memory of the body is maintained in this tissue.

Moreover, as discussed in chapters 10, 29, memories are sometimes unilaterally stored; i.e. the left hemisphere maintains a somesthetic-memory image of the right half of the body, the right cerebrum maintaining perhaps bilateral representations. In this regard, the left brain may in fact have no memory regarding the left half of the body.

Of course, all this seems preposterous, and yet, patients (i.e. the speaking half of their brain) will deny what is obvious, i.e. the existence or ownership of the left half of their body.

Inevitably, in order for an individual to confabulate, erroneous information must become integrated in some fashion so that the confabulated rsponse can be expressed. When the frontal lobes are compromised there is much flooding of the association and assimilation areas with tangential and irrelevant information much of which is amplified completely out of proportion to more salient details (Fischer et al. 1995; Joseph, 1986a, 1988a, 1993; Stuss et al. 1978). Consequently, salient and irrelevant, highly arousing and fanciful information are expressed indiscriminantly. The normal filtering process is disrupted. However, when the parietal lobes are compromised, rather than flooding, there results a disconnection and information received in the Language Axis is incomplete and riddled with gaps (Joseph, 1986a).

As noted, assimilation of input from diverse sources is a major feature of left and right parietal (i.e. inferior parietal) activity. Hence, when this area is damaged errors abound in the assimilation of perceptions and ideas as the language axis can no longer access all necessary information.

That is, when the language axis is functionally isolated from a particular source of information about which the patient is questioned (such as in cases of denial), it begins to make up a response based on the information available. To be informed about the left leg or left arm, it must be able to communicate with the cortical area (i.e. the parietal lobe) which is responsible for perceiving and analyzing information regarding the extremities. When no message is received and when the language axis is not informed that no messages are being transmitted, the language zones instead relie on some other source even when that source provides erroneous input (Joseph, 1986a); substitute material is assimilated and expressed and corrections cannot be made (due to loss of input from the relevant knowledge source). The patient begins to confabulate. According to Geschwind (1965), when the speech area is disconnected from a site of perception, then the speech area will be unable to describe what is going on at that site. This is because "the patient who speaks to you is not the 'patient' who is perceiving- they are in fact, separate".

In these instances delusions and confabulatory responses occur as a result of an attempt by the Language Axis to fill the gaps in the information received with associations and ideas which are in some manner related to the fragments available (Joseph, 1982, 1986a, Joseph et al. 1984; Talland, 1961). In this regard, confabulatory-delusional statements although erroneous, can contain some accurate elements around which erroneous, albeit related, ideations are anchored. Hence, a patient may see his left leg or arm and then state it belongs to the doctor. In general, these disturbances occur most frequently when the right frontal or right parietal lobe is damage. However, neglect, denial, and delusional confabulation may also infrequently result from left parietal injuries.






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