The Frontal lobes - Mahidol University

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19/07/54 Paul Broca (1824-1880) Tan’s Brain (removed in 1861) Now in the Museum of Man, Paris Expressive aphasia, known as Broca's aphasia in clinical neuropsychology and agrammatic aphasia in cognitive neuropsychology, is an aphasia caused by damage to or developmental issues in anterior regions of the brain, including (but not limited to) the left inferior frontal region known as Broca's area (Brodmann area 44 and Brodmann area 45) Presentation Sufferers of this form of aphasia exhibit the common problem of agrammatism. For them, speech is difficult to initiate, non‐fluent, labored, and halting. Similarly, writing is difficult as well. Intonation and stress patterns are deficient. Language g is reduced to disjointed words and sentence construction is poor, omitting function words and inflections (bound morphemes). A person with expressive aphasia might say "Son ... University ... Smart ... Boy ... Good ... Good ... " For example, in the following passage, a Broca's aphasic patient is trying to explain how he came to the hospital for dental surgery: Yes... ah... Monday... er... Dad and Peter H... (his own name), and Dad.... er... hospital... and ah... Wednesday... Wednesday, nine o'clock... and oh... Thursday... ten o'clock, ah doctors... two... an' doctors... and er... teeth... yah.[1] In extreme cases, patients may be only able to produce a single word. The most famous case of this was Paul Broca's patient Leborgne, nicknamed "Tan", after the only syllable he could say. Even in such cases, over-learned and rote-learned speech patterns may be retained—for instance, some patients can count from one to ten, but cannot produce the same numbers in ordinary conversation. While word comprehension is generally preserved, meaning interpretation dependent on syntax and phrase structure is substantially impaired. This can be demonstrated by using phrases with unusual structures. A typical Broca's aphasic patient will misinterpret "the dog is bitten by the man" by switching the subject and object. Patients who recover go on to say that they knew what they wanted to say but could not express themselves. Residual deficits will often be seen. Broca's area is a region of the hominid brain with functions linked to speech production. The production of language has been linked to the Broca’s area since Pierre Paul Broca reported impairments in two patients. They had lost the ability to speak after injury to the posterior inferior frontal gyrus of the brain. Since then, the approximate region he identified has become known as Broca’s area, and the deficit in language production as Broca’s aphasia. Broca’s area is now typically defined in terms of the pars opercularis and pars triangularis of the inferior frontal gyrus, represented in Brodmann’s cytoarchitectonic map as areas 44 and 45. Studies of chronic aphasia have implicated an essential role of Broca’s area in various speech and language functions. Further, functional MRI studies have also identified activation patterns in Broca’s area associated with various language tasks. However, slow destruction of the Broca's area by brain tumors can leave speech relatively intact suggesting its functions can shift to nearby areas in the brain. Brodmann area 44, , or BA44 44, is part of the frontal cortex in the human brain. Situated just anterior to premotor cortex (BA6) and on the lateral surface, inferior to BA9. This area is also known as pars opercularis (of the inferior frontal gyrus), and it refers to a subdivision of the cytoarchitecturally defined frontal region of cerebral cortex. In the human it corresponds approximately to the opercular part of inferior frontal gyrus (H). Thus, it is bounded caudally by the inferior precentral sulcus (H) and rostrally by the anterior ascending limb of lateral sulcus (H). It surrounds the diagonal sulcus (H). In the depth of the lateral sulcus it borders on the insula. Cytoarchitectonically it is bounded caudally and dorsally by the agranular frontal area 6, dorsally by the granular frontal area 9 and rostrally by the triangular area 45 (Brodmann‐1909). Together with left‐hemisphere BA 45, the left hemisphere . BA 44 comprises Broca's area a region involved in semantic tasks. Some data suggest that BA44 is more involved in phonological and syntactic processing. Some recent findings also suggest the implication of this region in music perception. In 95.5% of righthanders and 61.4% of left‐handers, therefore about 90% of the clinical population, speech is lateralised in the left hemisphere. Brain: Brodmann area 44 7/19/2011 NEUROPSYCHIATRY 143 24
19/07/54 Brodmann area 45 (BA45), is part of the frontal cortex in the human brain. Situated on the lateral surface, inferior to BA9 and adjacent to BA46. This area is also known as pars triangular (of the inferior frontal gyrus). In the human, it occupies the triangular part of inferior frontal gyrus (H) and, surrounding the anterior horizontal limb of lateral sulcus (H), a portion of the orbital part of inferior frontal gyrus (H). Bounded caudally by the anterior ascending limb of lateral sulcus (H), it borders on the insula in the depth of the lateral sulcus. Cytoarchitectonically it is bounded caudally by the opercular area 44 (BA44), rostrodorsally by the middle frontal area 46 (BA46) and ventrally by the orbital area 47 (BA47) (Brodmann‐1909). Together with BA 44 it comprises Broca's area, a region which is active in semantic tasks, such as semantic decision tasks (determining whether a word represents an abstract or a concrete entity) and generation tasks (generating a verb associated with a noun). The precise role of BA45 in semantic tasks remains controversial. For some researchers, its role would be to subserve semantic retrieval or semantic working memory processes. Under this view, BA44 and BA45 would together guide recovery of semantic information and evaluate the recovered information with regards to the criterion appropriate to a given context. A slightly modified account of this view is that activation of BA45 is needed only under controlled semantic retrieval, when strong stimulus‐stimulus associations are absent. For other researchers, BA45's role is not restricted to semantics per se, but to all activities which require task‐relevant representations from among competing representations. Brain: Brodmann area 45 Brodmann area 47, , or BA47 47, is part of the frontal cortex in the human brain. Curving from the lateral surface of the frontal lobe into the ventral (orbital) frontal cortex. It is below areas BA10 and BA45, and beside BA11. This area is also known as orbital area 47. In the human, on the orbital surface it surrounds the caudal portion of the orbital sulcus (H) from which it extends laterally into the orbital part of inferior frontal gyrus (H). Cytoarchitectonically yoac eco cayit is bounded caudally by the triangular area 45, medially by the prefrontal area 11 of Brodmann‐1909, and rostrally by the frontopolar area 10 (Brodmann‐1909). It incorporates the region that Brodmann identified as "Area 12" in the monkey, and therefore, following the suggestion of Michael Petrides, some contemporary neuroscientists refer to the region as "BA47/12." BA47 has been implicated in the processing of syntax in spoken and signed languages, and more recently in musical syntax. Brain: Brodmann area 47 The Wernicke's area is classically located as the posterior section of the superior temporal gyrus (STG) in the left (or dominant) cerebral hemisphere. This area encircles the auditory cortex on the Sylvian fissure (part of the brain where the temporal lobe and parietal lobe meet). This area is neuroanatomically described as the posterior part of Brodmann area 22. However, there is an absence of consistent definitions as to its location. Some identify it with the unimodal auditory association in the superior temporal gyrus anterior to the primary auditory cortex. Others include also adjacent parts of the heteromodal cortex in BA 39 and BA40 in the parietal lobe. While previously thought to connect Wernicke's area and Broca's area, new research demonstrates that the arcuate fasciculus instead connects to posterior receptive areas with premotor/motor areas, and not to Broca's area Wernicke and aphasia Wernicke's area is named after Carl Wernicke, a German neurologist and psychiatrist who, in 1874, hypothesized a link between the left posterior section of the superior temporal gyrus and the reflexive mimicking of words and their syllables that associated the sensory and motor images of spoken words. He did this on the basis of the location of brain injuries that caused aphasia. Receptive aphasia in which such abilities are preserved is now sometimes called Wernicke's aphasia. In this condition there is a major impairment of language comprehension, while speech retains a natural‐sounding rhythm and a relatively normal syntax. Language as a result is largely meaningless (a condition sometimes called fluent or jargon aphasia). While neuroimaging and lesion evidence generally support the idea that malfunction of or damage to Wernicke's area is common in people with receptive aphasia, this is not always so. Some people may use the right hemisphere for language, and isolated damage of Wernicke's area cortex (sparing white matter and other areas) may not cause severe receptive aphasia. Even when patients with Wernicke's area lesions have comprehension deficits, these are usually not restricted to language processing alone. For example, one study found that patients with posterior lesions also had trouble understanding nonverbal sounds like animal and machine noises. In fact, for Wernicke's area, the impairments in nonverbal sounds were statistically stronger than for verbal sounds. Right homologous area Research using Transcranial magnetic stimulation suggests that the area corresponding to the Wernicke’s area in the non‐dominant cerebral hemisphere has a role in processing and resolution of subordinate meanings of ambiguous words—such as (‘‘river’’) when given the ambiguous word (‘‘bank’’). In contrast, the Wernicke's area in the dominant hemisphere processes dominant word meanings (‘‘teller’’ given ‘‘bank’’). 25
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