For example, a patient with apraxia would have difficulty demonstrating how to take a cigarette out of pack, open up a pack of matches, and then light and puff on the cigarette. They would get the steps out of order and the movements might be quite clumsy.

Apraxia is most commonly associated with injuries to the parietal lobe, with left parietal lesions producing symptoms distinct from those associated with injuries to the right half of the brain or the left anterior region of the cerebrum. In this regard, there are in fact several different types of apraxias, which differ depending on which region of the brain has been injured.

These include, Ideational Apraxia, Ideomotor Apraxia, Bucal Facial Apraxia, and Dressing Apraxia. With the exception of dressing and constructional apraxia (which is due to a right cerebral injury), apraxic abnormalities are usually secondary to injuries involving the left frontal and inferior-superior parietal lobe.

THE SENSORY GUIDANCE OF MOVEMENT

Apraxia is associated with injuries to the parietal lobe which interacts with the frontal motor areas in the sensory guidance of movement, which is why the frontal-parietal lobe has been referred to as the sensorimotor cortex.

Specifically, in order for a movement to be correctly planned and carried out signals must be directed to the right muscle groups as based on efferent streams of visual, somesthetic, as well as auditory input. This includes information regarding the position of the body and limbs in space. Indeed, movement becomes extremely difficulty without sensory feedback and guidance. Because of this, parietal lesions can result in unilateral paresis and even wasting (i.e. parietal wasting). Hence, the somesthetic/parietal cortex is very important in the guidance of movement, and in fact some neurons fire prior to making a movement (Lebedev et al. 2011).

Although the entire parietal lobule makes important contributions , the superior and inferior parietal lobule of the left hemisphere appears to be the central region of concern in regard to the performance of skilled temporal-sequential motor acts. This is because the motor engrams for performing these acts appear to be stored in the left angular and supramarginal gyri (Geschwind, 1965; Heilman, 1993).

Indeed, the inferior and superior parietal lobe act to guide, visually observe, and can selectively learn hand movements, gestures, and complex temporal sequential actions such as involving tool construction (Joseph 1993, 2009e).

Movement and skilled movement memories are stored in the parietal cortex. These hand movement related memories assist in the programing of the motor frontal cortex where the actions are actually executed via the primary and secondary motor cortex.

APRAXIA

If the left inferior-superior parietal region is destroyed the patient will lose the ability to perform actions in an appropriate temporal-sequence. These patients also are unable to learn or perform tasks involving sequential changes in the hand or upper musculature (Kimura, 1979, 1982, 1993), including well learned, skilled, and even stereotyped motor tasks such as lighting a cigarette or using a key.

Patients perform most poorly when they are required to imitate or pantomime certain actions including the correct usage of some object (McDonald et al. 2011). That is, they do better if they have the actual object in front of them and in hand.

If the patient is asked to show the examiner, "how you would use a key to open a door", or "hammar a nail into a piece of wood" and to pretend they are using the key or hammer, they do extremely poorly and may use a body part in place of the actual object, i.e. a finger, as a a key. In this regard, however, there movements still remain abnormal. For example, rather than the finger and thumb holding the key they use the finger as the key. Again, however, performance usually improves when they use the real objects.

Patient's with apraxia have difficulty properly sequencing their actions even when performing well learned tasks . For example, they may pretend to stir a cup of coffee, then pretend to pour the coffee into the cup, and then take a sip. However, the individual acts may be performed accurately.

Broadly speaking, there are several forms of apraxia, which like many of the disturbances already discussed may be due to a number of causes or anatomical lesions. These include, ideational apraxia, ideomotor apraxia, bucal facial apraxia, constructional apraxia and dressing apraxia. With the exception of dressing and constructional apraxia, apraxic abnormalities are usually secondary to left hemisphere damage, in particular, injuries involving the the left frontal and inferior parietal lobes.

For example, Kimura (1982, 1993) found that the ability to perform meaningless oral or hand movements was related to the frontal or posterior nature of the lesion, such that those with frontal lesions were impaired on oral whereas those with parietal lesions had the most difficulty making hand postures or complex movements of the extremities (Kolb & Milner, 1981). Thus, apraxic abnormalities secondary to left cerebral lesions tend to either involve destruction of the inferior parietal lobule (IFP) or lesions resulting in disconnection of the frontal motor areas (or the right cerebral hemisphere) from this more posterior region of the brain.

If the inferior parietal region is destroyed the patient loses the ability to appreciate when they have performed an action incorrectly. If the motor region is destroyed, although the act is still performed inaccurately (due to disconnection from the IFP), the patient is able to recognize the difference (Heilman, 1993; Kimura 1993).

IDEOMOTOR APRAXIA

Ideomotor apraxia is usually associated with lesions within the inferior parietal lobe of the left hemisphere. Rather than problems with temporal-sequencing of motor acts per se, these individuals tend to be very clumsy when performing an act, and/or they may perseverate and erroneously perform a previous movement. These individuals also tend to be very deficient when attempting to perform an action via pantomime or when engaged in meaningful imitation, meaningless imitation, and the meaingful use or meaningless use of actual objects (Goodlass & Kaplan, 1972; Heilman, 1973; Kimura & Archibald, 1974; McDonald et al. 2011). This is presumably due to destruction of the engrams important in motor performance. Patients will demonstrate apraxic abnormalities in both the right and left hand.

In addition, patients with ideomotor apraxia tend to have difficulty with simple versus complex movements, although various elements within a complex action may be performed somewhat abnormal (Hecaen & Albert, 1978; McDonald et al. 2011). Hence, actions such as waving goodbye, throwing a kiss, making the "sign of the cross", may be performed deficiently. Moreover, many patients tend to uncontrollably comment on their actions; i.e. "verbal overflow". That is, when asked to "wave goodbye", they may say "goodbye" while waving even when instructed to say nothing.

It has been suggested that ideomotor apraxia can occur in the absence of ideational apraxia, but that the converse is not true (Hecaen & Albert, 1978). In this regard, ideomotor apraxia may be a less severe form of ideational apraxia (Kimura 1993).

IDEATIONAL APRAXIA

This form of apraxia is usually due to severe disturbances in the temporal sequencing of motor acts (Buxbaum et al., 2014). That is, the separate chain of links which constitute an entire movement become dissociated, such that the overriding idea of the movement in it's entirety is lost. Hence, these individuals commit a number of temporal and spatial errors when making skilled movements, although the individual elements, in isolation, may be preserved and performed accurately (Hecaen & Albert, 1978; Luria, 1980). For example a patient (via pantomime) may rotate their hand before inserting the key, drink from a cup before filling it from a pitcher of water, or puff from a cigarette and then lighting it. Thus they incorrectly sequence a series of acts. Both hands are effected.

Because of conceptual, ideational abnormalities, they may also have difficulty using actual objects correctly. During pantomime they may use a body part as object such as an index finger for a key. Even so, their actions are out of temporal sequence. Hence, these patients seem to be unable to access the motor engrams (or "memories") which would allow them to perform appropriately (Luria, 1980). In this regard, patients are sometimes hesisant to perform a task as they have difficulty understanding what has been asked of them. However, they can often describe verbally what they are unable to perform (Heilman, 1993).

LEFT SIDED OR UNILATERAL APRAXIA (also called Callosal & frontal apraxia)

Patients with unilateral (callosal/frontal) apraxia are unable to imitate or perform certain movements with their left (but not right) hand and are clumsy in their use of objects. Left sided apraxia is sometimes due to a lesion of the anterior corpus callosum or left frontal motor cortex. This is because lesions of the corpus callosum or premotor and motor region of the left hemisphere can result in a disconnection syndrome; i.e. the motor areas of the right hemisphere cannot gain access to the motor engrams stored within the left inferior parietal lobe. Thus, with a left frontal lesion there results an apraxia of the left hand and paralysis of the right. Often this is secondary to strokes within the distribution of the anterior cerebral artery such that the anterior portion of the corpus callsom is destroyed (Geschwind, 1965).

It is noteworthy that patients also may show deficient finger tapping performance in the left hand due to apraxic abnormalities secondary to left hemisphere injury (Heilman, 1975). In these instances, reduced finger tapping is bilateral.

DRESSING APRAXIA

Dressing apraxia is usually secondary to right hemisphere lesions involving the inferior parietal region, and as the name implies, the patient has difficulty putting on their clothes. For example, a patient may attempt to put a shirt on upside down, then inside-out, and then backwards. Severe spatial-perceptual abnormalities as well as body image disturbances are usually contributing factors.

Aphasia & Apraxia

Many patients who are aphasic also appear apraxic because they have severe difficulty comprehending language and understanding motor commands. That is, a patient may fail to perform a particular action because he doesn't comprehend what is being asked.

To distinguish between receptive aphasic abnormalities and apraxia one must ask "yes" and "no" questions ("are you in a hospital?"); require them to perform certain actions via pantomime ("show me how you would throw a ball" or "show me how a soldier salutes"); as well require pointing response ("point to the lamp"). If they can answer appropriately "yes" or "no" or point to objects named but cannot execute commands they have apraxia. It is important to note that in severe cases apraxic patients may have difficulty even with pointing.

PANTOMIME RECOGNITION

Individuals with damage involving the left parietal lobule not only make errors when performing motor acts but comprehending, recognizing and discriminating between different types of motor acts such as demonstrated via pantomime (Heilman et al. 1982; McDonald et al. 2011). Moreover, individuals with lesions in the left inferior occipital lobe have also been shown to have difficulty verbally understanding, describing or differentiating between pantomimes (Rothi et al. 2003). That is, in the extreme, if one were to pantomime the pouring of water into a glass vs. lighting and smoking a cigarette, these individuals have problems describing what they have viewed or in choosing which was which.

Deficits in pantomime recognition occur frequently among individuals with aphasia (Varney, 1978). Moreover, this disturbance is also significantly correlated with reading comprehension (Gainotti & Lemmo, 1976; Varney, 1978, 1982). In this regard, individuals with alexia frequently suffer from pantomime recognition deficits as well. Because of this relationship it has been suggested that the ability to read may be based on or derived from the abiiity to understand gestural communication, i.e. the reading of signs (Joseph 1993; Varney, 1982).

Wang and Goodglass (1992) and Kimura (1993) argue that pantomime imitation and production are related to both apraxia and the ability to interpret purposeful movements; the engrams for which are located in the inferior parietal lobule (Heilman et al. 1982; Joseph 1993; Wang & Goodglass, 1992). By contrast to left anterior lesions which may impair motor functioning and the capacity to imitate the ability to comprehend pantomime is retained (Heilman et al. 1982).

As noted, the inferior and superior parietal lobule receives considerable visual input, particularly from the periphery and lower visual field -the area in which the hands are most likely to be viewed. Hence, this area of the brain views, manipulates, guides and mediates hand-object coordination and reaching movements, including the comprehension of hand movements; i.e. gestures (Joseph, 1993). Hence, when the left superior and inferior parietal lobule is destroyed gestural comprehension, including the understanding of (as well as the capacity to execute) complex gestures, including ASL and the capacity to engage in complex temporal sequential acts is significantly impacted. If the right parietal area is destroyed, these deficits may also include constructional apraxia (chapter 10).

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 unnecessary/non-existent details or parts, misalignment or inattention to details, disruptions of the horizontal and vertical 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., 2005; 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., 2005; 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.