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Broca's Area

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




Broca's Area: Broca's Expressive (Motor) Aphasia


by Rhawn Joseph, Ph.D.

MOVEMENT AND THE MOTOR AREAS OF THE FRONTAL LOBES

BROCA'S AREA & BROCA'S EXPRESSIVE MOTOR APHASIA

BROCA'S EXPRESSIVE APHASIA

Broca's speech are is located in the general vicinity of the posterior- inferior region of the left frontal area (i.e. third frontal convolution), and includes portions of areas 45, 6, 4, and all of area 44. This region is multimodally responsive (Passingham, 1997) and receives projections from the auditory, visual, somesthetic areas (Geschwind, 1965; Jones & Powell, 1970), as well as massive input from the inferior parietal lobule and Wernicke's area via a rope of nerve fibers referred to as the arcuate fasciculus (which also links these areas to the amygdala). In addition, Broca's area receives fibers from and projects to the anterior cingulate as well as the brainstem periaqueductal gray which subserves vocalization.

Broca's speech area is a final converging destination point through which thought and other impluses come to receive their final sequential (syntactical, grammatical) inprint so as to become organized and expressed as temporally ordered motoric articulations; i.e. speech (Foerster 1936; Fox 1995; Goodglass, 1993; Goodglass & Kaplan, 2000; Kimura, 1993; LeBlanc 1992; Petersen et al. 1988, 1990; Sarno, 1998). Verbal communication, the writing of words (via transmission to Exner's area), and the expression of thought in linguistic form is made possible via Broca's area which programs the adjacent oral-laryngeal musculature as represented within the adjacent primary motor areas (Foerster 1936; Fox 1995; Kimura, 1993; LeBlanc 1992; Petersen et al. 1988, 1990; Sarno, 1998); and which transmits to Exner's writing area so that words may be written.

The importance of Broca's area and the left frontal lobe has also been demonstrated through functional imaging. For example, the left frontal lobe becomes activated during inner speech and subvocal articulation (Paulesu, et al., 1993; Demonet, et al., 1994). The left frontal lobe also becomes highly active when reading concrete and abstract words (Buchel et al., 1998; Peterson et al., 1988), and when engaged in semantic decision making tasks (Demb et al., 1995; Gabrielli et al., 1996). Moreover, activation increases as word length increases and in response to long and umfamiliar words (Price, 1997).

With injuries to Broca's area the individual loses the capacity to produce fluent speech (Goodglass, 1993; Goodglass & Kaplan, 2000; Sarno, 1998). Output becomes extremely labored, sparse, and difficult, and they may be unable to say even single words, such as "yes" or "no". Often, immediately following a large stroke patients are almost completely mute and suffer a paralysis of the upper right extremity as well as right facial weakness (since these areas are neuronally represented in the immediately adjacent area 4). Patients are also unable to write, read out loud or repeat simple words. Interestingly, it has been repeatedly noted that almost immediately following stroke some patients will announce "I can't talk", and then lapse into frustrated partial mutism.

With less severe forms of Broca's (also referred to as expressive, motor, nonfluent, verbal) aphasia, speech remains labored, agrammatical, fragmented, extremely limited to stereotyped phrases ("yes", "no", "shit", "fine") and contaminated with syntactic and paraphasic errors i.e. "orroble" for auto, "rutton" for button (Bastiaanse, 1995; Goodglass, 1993; Goodglass & Kaplan, 1999; Haarmann & Kolk 1994; Hofstede & Kolk 1994; Levine & Sweet, 1982, 1983; Sarno, 1998; Tramo et al. 1988). Writing remains severely effected, as are oral reading and repetition. Such patients also have mild difficulties with verbal perception and comprehension (Hebben, 1986; Maher et al. 1994; Tramo et al., 1988; Sarno, 1998; Tyler et al. 1995), including the ability to follow 3-step commands (Lura 1980). Commands to purse or smack the lips, lick, suck, or blow are often, but not always, poorly executed (DeRenzi et al. 1966; Kimura 1993); a condition referred to as bucal-facial apraxia. Non-speech oral movements are seldom significantly effected (Goodglass & Kaplan, 1999; Hecaen & Albert, 1978; Kimura 1993; Levine & Sweet, 1983).

With mild damage, patients may demonstrate severe confrontive naming and word finding difficulties (anomia), as well as possible right facial, hand, and arm weakness. Speech is often characterized by long pauses, misnaming, paraphasic disturbances and articulatory abnormalities (Goodglass, 1993; Goodglass & Kaplan, 1999; Sarno, 1998). Stammering and the omission of words may also be apparent. Similarly, electrical stimulation of this region results in speech arrest (Ojemann & Whitaker, 1978; Lesser et al., 1984) and can alter the ability to write and/or perform various oral-facial movements. It is noteworthy that even with anterior lesions or surgical frontal lobectomy sparing Broca's area a considerable impoverishment of spontaneous speech can result (Luria, 1980; Milner, 1971; Novoa & Ardila, 1987). Disturbances involving grammar and syntax, and reductions in vocabulary and word fluency in both speech and writing have been observed with frontal lesions sparing Broca's area (Benson, 1967; Crockett, Bilsker, Hurwitz, & Kozak, 1986; Goodglass & Berko, 1960; Milner, 1964; Novoa & Ardila, 1987; Petrie, 1952; Samuels & Benson, 1979; Stuss, et al., 1998; Tow, 1955). In word fluency tests, however, simple verbal generation (e.g. all words starting with L) is usually more severely impaired than semantic naming, e.g. all animals which live in the jungle--which is presumably a function of semantic processing being more dependent on posterior language areas (Stuss et al., 1998).








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