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+ | IsPartOf = [[Frontal lobe]]| |
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+ | Artery = [[Middle cerebral artery|Middle cerebral]]| |
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+ | Vein = [[Superior sagittal sinus]]| |
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| + | '''Broca's area''' is a region of the [[brain]] with functions linked to [[speech production]]. |
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| − | '''Broca's area''' is the section of the human [[brain]] (in the opercular and triangular sections of the [[inferior frontal gyrus]] of the [[frontal lobe]] of the [[Cerebral cortex|cortex]]) that is involved in [[language processing]], [[speech]] production and comprehension. Broca's and Wernicke's areas are found unilaterally in the brain. |
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| + | The production of [[language]] has been linked to the Broca’s area since [[Paul Pierre Broca]] reported impairments in two patients. They had lost the ability to speak after injury to the posterior [[inferior frontal gyrus]] of the brain.<ref name="pmid17405763">{{cite journal | author=N. F. Dronkers, O. Plaisant, M. T. Iba-Zizen, and E. A. Cabanis | title=Paul Broca's Historic Cases: High Resolution MR Imaging of the Brains of Leborgne and Lelong| journal=Brain | year=2007| volume=130| page=1432–1441 |pmid=17405763 |doi=10.1093/brain/awm042 }}</ref> 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 [[Korbinian Brodmann|Brodmann]]’s [[Cytoarchitectonics|cytoarchitectonic]] map as areas [[Brodmann area 44|44]] and [[Brodmann area 45|45]].<ref name="pmid17405763" /> 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 [[tumor]]s can leave speech relatively intact suggesting its functions can shift to nearby areas in the brain.<ref name="Plaza">Plaza M, Gatignol P, Leroy M, Duffau H. (2009). Speaking without Broca's area after tumor resection. Neurocase.9:1-17. PMID 19274574</ref> |
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| − | It comprises of Brodmann's Area [[Brodmann area 44|44]],<ref>Mohr JP in ''Studies in Neurolinguistics'' (eds. Witaker H & Witaker NA) 201–235 (Academic, New York, 1976)</ref> and some authorities also include Brodmann's Area [[Brodmann area 45|45]]<ref>Penfield W & Roberts L ''Speech and Brain Mechanisms'' (Princeton Univ Press, Princeton, 1959)</ref><ref>{{cite journal | author=Ojemann GA, Ojemann JG, Lettich E, Berger MS | title=Cortical language localization in left, dominant hemisphere. An electical stimulation mapping investigation in 117 patients | year=1989 | journal=J Neurosurg | volume=71 | pages=316–26 }}</ref><ref>{{cite journal | author=Duffau H ''et al.'' | title=The role of dominant premotor cortex in language: a study uding intraoperative functional mapping in awake patients | year=2003 | journal=Neuroimage | volume=20 | pages=1903–14 }}</ref>); Broca's Area is connected to [[Wernicke's area]] by a [[neural pathway]] called the [[arcuate fasciculus]]. The corresponding area in macaque monkeys is responsible for high-level control over orofacial actions.<ref>{{cite journal | author=Petrides M, Cadoret G, Mackey S | title=Orofacial somatomotor responses in the macaque monkey homologue of Broca's area | year=2005 | journal=Nature | volume=435 | pages=1235–38 | doi=10.1038/nature03628 }}</ref> |
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| + | ==Anatomy and connectivity== |
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| − | ==Etymology== |
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| − | Broca's area is named after [[Pierre Paul Broca]], who first described it in [[1861]], after conducting a [[post mortem]] study on a speech-impaired patient. |
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| + | Broca's area is often identified by visual inspection of the [[topography]] of the brain either by macrostructural landmarks such as [[Sulcus_(neuroanatomy)|sulci]] or by the specification of coordinates in a particular reference space. The currently used Talairach and Tournoux atlas projects [[Korbinian Brodmann|Brodmann]]'s cytoarchitectonic map on to a template brain. Because Brodmann's parcelation was based on subjective visual inspection of cytoarchitectonic borders and also Brodmann analyzed only one hemisphere of one brain, the result is imprecise. Further, because of considerable variability across brains in terms of shape, size, and position relative to sulcal and gyral structure, a resulting localization precision is limited.<ref name="pmid18930695">{{cite journal | author=Yosef Grodzinsky and Andrea Santi| title=The Battle for Broca's Region | journal=Trends in Cognitive Sciences| year=2002| volume=12| issue=12| page=474–480 |pmid=18930695 |doi=10.1016/j.tics.2008.09.001}}</ref> |
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| − | ==Parts== |
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| + | |||
| − | There are two main parts of Broca's area, which express different roles during language comprehension and production: |
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| + | Nevertheless, Broca’s area in the left hemisphere and its homologue in the right [[Cerebral hemisphere|hemisphere]] are designations usually used to refer to [[pars triangularis]] (PTr) and [[pars opercularis]] (POp) of the inferior frontal [[gyrus]]. The PTr and POp are defined by structural landmarks that only probabilistically divide the inferior frontal gyrus into anterior and posterior cytoarchitectonic areas of 45 and 44, respectively, by [[Brodmann]]’s classification scheme.<ref name="pmid17533001">{{cite journal | author=Jeremy I. Skipper, Susan Goldin-Meadow, Howard C. Nusbaum, and Steven L. Small| title=Speech-Associated Gestures, Broca's Area, and the Human Mirror System | journal=Brain and Language| year=2007| volume=101| page=260–277 |pmid=17533001 |doi=10.1016/j.bandl.2007.02.008}}</ref> |
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| − | * ''[[Pars triangularis]]'' (anterior), which is thought to support the interpretation of various 'modes' of [[stimulation|stimuli]] ([[plurimodal association]]) and the programming of verbal conducts |
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| + | |||
| − | * ''[[Pars opercularis]]'' (posterior), which is thought to support the management of only one kind of stimulus ([[unimodal association]]) and the coordination of the speech organs for the actual production of language, given its favorable position close to motor-related areas. |
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| + | Area 45 receives more afferent connections from prefrontal cortex, the superior temporal [[gyrus]], and the superior temporal [[sulcus]], compared to area 44, which tends to receive more afferent connections from motor, [[somatosensory]], and inferior parietal regions.<ref name="pmid17533001" /> |
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| + | |||
| + | The differences between area 45 and 44 in cytoarchitecture and in connectivity suggest that these areas might perform different functions. Indeed, recent [[neuroimaging]] studies have shown that the PTr and Pop, coressponding to areas 45 and 44, respectively, play different functional roles in the human with respect to language comprehension and action recognition/understanding.<ref name="pmid17533001" /> |
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| + | |||
| + | ==Broca's area revisited== |
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| + | In a recent study, the preserved brains of both Leborgne and Lelong (patients of [[Paul Pierre Broca]]) were reinspected using high-resolution volumetric [[MRI]]. The purpose of this study was to scan the brains in three dimensions and to identify the extent of both cortical and subcortical lesions in more detail. The study also sought to locate the exact site of the lesion in the frontal lobe in relation to what is now called Broca's area with the extent of subcortical involvement.<ref name="pmid17405763" /> |
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| + | |||
| + | ===Broca's patients=== |
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| + | ====Leborgne==== |
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| + | |||
| + | Leborgne was a patient of [[Paul Pierre Broca]]. He was unable to produce any words or phrases. The only word he could repetitively produce was 'tan'. After his death, a lesion was discovered on the surface of the left frontal lobe. |
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| + | |||
| + | ====Lelong==== |
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| + | |||
| + | Lelong was another patient of [[Paul Pierre Broca]]. He also exhibited reduced productive speech. He could only say five words, 'yes,' 'no,' 'three,' 'always,' and 'lelo' (a mispronunciation of his own name). At autopsy, a lesion was also found in the same region of lateral frontal lobe as in Leborgne. These two cases led [[Paul Pierre Broca]] to believe that speech was localized to this particular area. |
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| + | |||
| + | ===MRI findings=== |
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| + | |||
| + | Examination of the brains of [[Paul Pierre Broca]]'s two historic patients with high resolution [[MRI]] has produced several interesting findings. First, the MRI findings suggest that other areas besides Broca's area may also have contributed to the patients' reduced productive speech. This finding is significant because it has been found that though [[lesions]] to Broca's area alone can possibly cause temporary speech disruption, they do not result in severe speech arrest. Therefore, there is a possibility that the [[aphasia]] denoted by Broca as an absence of productive speech also could have been influenced by the lesions in the other region. Another interesting finding is that the lesion, which was once considered to be critical for speech by Broca, is not precisely the same region as what is now known as Broca's area. This study provides further evidence that language and cognition are far more complicated than once thought and involve various networks of brain regions. |
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| + | |||
| + | ===Speaking without Broca’s area=== |
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| + | |||
| + | The essential role of the Broca's area in speech production has been questioned since it can be destroyed while leaving language nearly intact. In one case of a computer engineer a slow growing [[glioma]] was removed. The tumor and the surgery destroyed the left [[inferior frontal gyrus|inferior]] and [[middle frontal gyrus]], the head of the [[caudate nucleus]], the anterior limb of the [[internal capsule]] and the anterior [[insula]]. However there were minimal language problems three months after removal and the individual returned to his professional work. These minor problems include the inability to create syntactically complex sentences with including more than two subjects, multiple causal [[conjunction]]s or [[reported speech]]. These were explained by researchers as due to [[working memory]] problems. They also attributed his lack of problems to extensive compensatory mechanisms enabled by [[neural plasticity]] in the nearby cerebral cortex and a shift of some functions to the homologous area in the right hemisphere.<ref name="Plaza"/> |
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| + | |||
| + | ==Functions== |
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| + | ===Language comprehension=== |
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| + | |||
| + | For a long time, it was assumed that the role of Broca's area was more devoted to language production than language comprehension. However, recent evidence demonstrates that Broca's area also plays a significant role in language comprehension. Patients with [[lesions]] in Broca's area who exhibit agrammatical speech production also show inability to use syntactic information to determine the meaning of sentences.<ref name="pmid16881251">{{cite journal | author=David Caplan | title=Why is Broca's Area Involved in Syntax?| journal=Cortex | year=2006| volume=42| page=469–471 |pmid=16881251}}</ref> Also, a number of neuroimaging studies have implicated an involvement of Broca's area, particularly of the [[pars opercularis]] of the left inferior frontal [[gyrus]], during the processing of complex sentences.<ref name="pmid15929098">{{cite journal | author=Tanja Crewe, Ina Bornkessel, Stefan Zysset, Richard Wiese, D. Yves von Cramon, and Matthias Schlesewksy | title=The Emergence of the Unmarked: A New Perspective on the Language-Specific Function of Broca's Area| journal=Human Brain Mapping | year=2005| volume=26| page=178–190 |pmid=15929098 |doi=10.1002/hbm.20154}}</ref> Further, it has recently been found in functional magnetic resonance imaging ([[fMRI]]) experiments involving highly ambiguous sentences result in a more activated inferior frontal [[gyrus]].<ref name="pmid17533001" /> Therefore, the activity level in the inferior frontal gyrus and the level of lexical ambiguity are directly proportional to each other, because of the increased retrieval demands associated with highly ambiguous content. |
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| + | |||
| + | ===Action recognition and production=== |
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| + | |||
| + | Recent experiments have indicated that Broca's area is involved in various cognitive and perceptual tasks. One important contribution of [[Brodmann]]'s area 44 is also found in the motor-related processes. Observation of meaningful hand shadows resembling moving animals activates frontal language area, demonstrating that Broca's area indeed plays a role in interpreting action of others.<ref name="pmid18633777">{{cite journal | author=Luciano Fadiga, Laila Craighero, Maddalena Fabbri Destro, Livio Finos, Nathalie Cotilon-Williams, Andrew T. Smith, and Umberto Castiello| title=Language in Shadow| journal=Social Neuroscience| year=2006| volume=1| issue=2| page=77–89 |pmid=18633777 |doi=10.1080/17470910600976430}}</ref> An activation of BA 44 was also reported during execution of grasping and manipulation.<ref name="pmid16881255">{{cite journal | author=Luciano Fadiga and Laila Craighero | title=Hand Actions and Speech Representation In Broca's Area| journal=Cortex| year=2006| volume=42| page=486–490 |pmid=16881255}}</ref> |
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| + | |||
| + | ===Speech-associated gestures=== |
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| + | |||
| + | It has been speculated that because speech-associated gestures could possibly reduce lexical or sentential ambiguity, comprehension should improve in the presence of speech-associated gestures. As a result of improved comprehension, the involvement of Broca's area should be reduced.<ref name="pmid17533001" /> |
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| + | |||
| + | Many neuroimaging studies have also shown activation of Broca's area when representing meaningful arm gestures. A recent study has shown evidence that word and gesture are related at the level of translation of particular gesture aspects such as goal and intention.<ref name="pmid16839281">{{cite journal | author=Maurizio Gentilucci, Paolo Bernardis, Girolamo Crisi, and Riccardo Dalla Volta| title=Repetitive Transcranial Magnetic Stimulation of Broca's Area Affects Verbal Responses to Gesture Observation | journal=Journal of Cognitive Neuroscience| year=2006| volume=18| issue=7| page=1059–1074 |pmid=16839281 |doi=10.1162/jocn.2006.18.7.1059}}</ref> This finding that aspects of gestures are translated in words within Broca's area also explains language development in terms of evolution. Indeed, many authors have proposed that speech evolved from a primitive communication that arose from gestures.<ref name="pmid18633777" />,<ref name="pmid12653308">{{cite journal | author=Philip Lieberman | title=On the Nature and Evolution of the Neural Bases of Human Language | journal=Yearbook of Physical Anthropology| year=2002| volume=45| page=36–62 |pmid=12653308}}</ref> (see '''Evolution of Language''' below) |
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==Aphasia== |
==Aphasia== |
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| − | People suffering from damage to this area may show a condition called ''[[Broca's aphasia]]'' (sometimes known as ''[[expressive aphasia]]'', ''motor aphasia'', or ''nonfluent aphasia''), which makes them unable to create grammatically-complex sentences: their speech is often described as telegraphic and contains little but content words. Patients usually are aware that they cannot speak properly. Comprehension in Broca's aphasia is relatively normal, although many studies have demonstrated that Broca's aphasics have trouble understanding certain kinds of syntactically complex sentences.<ref>{{cite journal | author=Caramazza A & Zurif E | title=Dissociation of algorithmic and heuristic processes in language comprehension: evidence from aphasia | year=1976 | journal=Brain and Language | volume=3 | pages=572–82 }}</ref> |
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| + | [[Aphasia]] is an acquired language disorder affecting all modalities such as writing, reading, speaking, and listening and results from brain damage. It is often a chronic condition that creates changes in all areas of one’s life.<ref name="Ref4">{{Cite web|url=http://www.atlantaaphasia.org|title=What is Aphasia|accessdate=2008-12-01|publisher=Atlanta Aphasia Association |year=2006}}</ref> |
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| − | This type of aphasia can be contrasted with [[Wernicke's aphasia]], named for [[Karl Wernicke]], which is characterized by damage to more posterior regions of the left hemisphere (in the superior [[temporal lobe]]). Wernicke's aphasia manifests as a more pronounced impairment in comprehension. Thus, while speech production remains normal grammatically, it is nonetheless often roundabout, vague or meaningless. It is therefore also known as [[receptive aphasia]]. |
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| + | '' |
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| + | ===Broca's aphasia vs. other aphasias=== |
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| − | For example, in the following passage, a Broca's aphasic patient is trying to explain how he came to the hospital for dental surgery. |
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| + | Patients with [[Broca's aphasia]] are individuals who know "what they want to say, they just cannot get it out." <ref name="Ref4" /> They are typically able to understand what is being said to them, but unable to fluently speak. This is also known as [[non-fluent aphasia]]. Some of other symptoms may include problems with fluency, articulation, word-finding, [[word repetition]], and producing and comprehending complex grammatical sentences, both orally and in writing.<ref name="pmid17405763" /> These characteristics distinguish them from other individuals with other types of aphasia. Other aphasia types may have more difficulty understanding what is said to them. They may also struggle more with reading and writing than do individuals with Broca’s aphasia. While the individuals with Broca’s aphasia also have a good ability to self-monitor their language output, other types of aphasia may be more unaware of their language performance. Also, site of [[lesion]] (brain damaged area) differs between the different aphasias. |
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| − | <blockquote>"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."<ref>Goodglass H & Geschwind N. Language disorders. In E. Carterette and M.P. Friedman (eds.) ''Handbook of Perception: Language and Speech. Vol II'' (New York, Academic Press, 1976)</ref> |
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| − | </blockquote> |
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| + | {| class="wikitable" border="1" |
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| − | PET and functional MRI have found decreases in activity in the Broca's area in stuttering.There is greater activation of the right hemisphere homologue of the Broca's area (area of Ross) which is believed to be a compensatory response to the hypoactivity in the Broca's area proper. |
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| + | |+Major Characteristics of Different Types of Aphasia'''<ref name="Ref4" /> |
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| − | Volumetric MRI has shown that the [[pars triangularis]] is smaller in people who stutter. |
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| + | ! Type of Aphasia |
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| + | ! Repetition |
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| + | ! Naming |
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| + | ! Auditory Comprehension |
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| + | ! Fluency |
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| + | |- |
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| ⚫ | |||
| + | | Mod-severe |
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| + | | Mod-severe |
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| + | | Mild difficulty |
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| + | | Non-fluent, effortful, slow |
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| + | |- |
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| + | | [[Receptive aphasia|Wernicke's]] |
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| + | | Mild-severe |
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| + | | Mild-severe |
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| + | | Defective |
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| + | | Fluent paraphasic |
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| + | |- |
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| + | | [[Conduction aphasia|Conduction]] |
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| + | | Poor |
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| + | | Poor |
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| + | | Relatively good |
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| + | | Fluent |
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| + | |- |
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| + | | Mixed Transcortical |
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| + | | Moderate |
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| + | | Poor |
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| + | | Poor |
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| + | | Non-fluent |
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| + | |- |
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| + | | Transcortical Motor |
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| + | | Good |
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| + | | Mild-severe |
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| + | | Mild |
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| + | | Non-fluent |
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| + | |- |
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| + | | Transcortical Sensory |
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| + | | Good |
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| + | | Mod-severe |
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| + | | Poor |
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| + | | Fluent |
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| + | |- |
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| + | | Global |
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| + | | Poor |
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| + | | Poor |
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| + | | Poor |
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| + | | Non-fluent |
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| + | |- |
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| ⚫ | |||
| + | | Mild |
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| + | | Mod-severe |
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| + | | Mild |
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| + | | Fluent |
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| + | |} |
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| + | |||
| + | ==Evolution of language== |
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| + | |||
| + | Several models have been proposed to explain the origin of human language. Human language is thought to have [[evolution|evolved]] as the “evolutionary refinement of an implicit communication system already present in lower primates, based on a set of hand/mouth goal-directed action representations.”<ref name="pmid18633777" /> The recent finding that Broca’s area is involved during meaningful action observation supports this idea. It was hypothesized that Broca’s area precursor was involved in generating action meanings by interpreting motor sequences in terms of goal. It was further argued that this ability might have been generalized during the evolution that gave this area the capability to deal with meanings. The activated frontal language areas when observing meaningful hand shadows resembling moving animals provides evidence that the human language may have evolved from neural substrates already involved in gestural recognition. Therefore, the study has demonstrated human Broca’s area as the motor center for speech, assembling and decoding communicative gestures. Consistent with this idea is that the neural substrate that regulated motor control in the common ancestor of apes and humans was most likely modified to enhance cognitive and linguistic ability.<ref name="pmid12653308" /> |
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| + | |||
| + | Another recent finding has showed significant areas of activation in subcortical and neocortical areas during the production of communicative manual gestures and vocal signals in chimpanzees.<ref name="pmid18308569">{{cite journal | author=Jared P. Taglialatela, Jamie L. Russell, Jennifer A. Schaeffer, and William D. Hopkins | title=Communicative Signaling Activates 'Broca's' Homolog in Chimpanzees| journal=Current Biology| year=2008| volume=18| page=343–348 |pmid=18308569 |doi=10.1016/j.cub.2008.01.049}}</ref> Further, the data indicating that chimpanzees intentionally produce manual gestures as well as vocal signals to communicate with humans suggests that the precursors to human language are present at both the behavioral and neuronanatomical levels. |
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| + | |||
| + | == Additional images == |
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| + | <gallery widths="200px" heights="200px" perrow="3"> |
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| + | File:Brodmann Cytoarchitectonics 44.png|[[Brodmann area 44]]. |
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| + | File:Brodmann Cytoarchitectonics 45.png|[[Brodmann area 45]]. |
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| + | </gallery> |
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==See also== |
==See also== |
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| + | |||
| + | * [[Broca's aphasia]] |
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| ⚫ | |||
* [[pars opercularis]] |
* [[pars opercularis]] |
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* [[pars triangularis]] |
* [[pars triangularis]] |
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| − | * [[arcuate fasciculus]] |
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| − | * [[Cerebral cortex|cortex]] |
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| ⚫ | |||
| − | * [[human brain]] |
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| − | * [[language]] |
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| − | * [[pars opercularis]] |
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| − | * [[pars triangularis]] |
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| ⚫ | |||
| − | * [[arcuate fasciculus]] |
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| − | * [[Cerebral cortex|cortex]] |
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| − | * [[human brain]] |
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| − | * [[language]] |
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| − | * [[Wernicke's area]] |
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| ⚫ | |||
==References== |
==References== |
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| − | <references/> |
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| − | {{ |
+ | {{reflist|2}} |
| + | |||
| + | {{Telencephalon}} |
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| + | |||
| + | {{DEFAULTSORT:Broca'S Area}} |
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| ⚫ | |||
| + | <!-- |
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| ⚫ | |||
| − | [[ |
+ | [[de:Broca-Areal]] |
| + | [[es:Área de Broca]] |
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| + | [[fr:Aire de Broca]] |
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| + | [[ko:브로카 영역]] |
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| + | [[id:Area Broca]] |
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| + | [[it:Area di Broca]] |
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| + | [[he:אזור ברוקה]] |
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| + | [[nl:Gebied van Broca]] |
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| + | [[ja:ブローカ野]] |
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| + | [[no:Brocas område]] |
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| + | [[pl:Ośrodek Broki]] |
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| + | [[pt:Área de Broca]] |
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| + | [[ru:Центр Брока]] |
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| + | [[fi:Brocan alue]] |
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| + | [[sv:Brocas område]] |
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| + | [[vls:Gebied van Broca]] |
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| + | [[zh:布若卡氏区]] |
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| + | --> |
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| + | {{enWP|Broca's area}} |
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Latest revision as of 13:22, 6 November 2012
Assessment |
Biopsychology |
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Biological: Behavioural genetics · Evolutionary psychology · Neuroanatomy · Neurochemistry · Neuroendocrinology · Neuroscience · Psychoneuroimmunology · Physiological Psychology · Psychopharmacology (Index, Outline)
| Brain: Broca's area | ||
|---|---|---|
 | ||
| Approximate location of Broca's area highlighted in gray | ||
 | ||
| Broca's area visible but not labeled. | ||
| Latin | ' | |
| Gray's | subject # | |
| Part of | Frontal lobe | |
| Components | ||
| Artery | Middle cerebral | |
| Vein | Superior sagittal sinus | |
| BrainInfo/UW | ancil-251 | |
| MeSH | [1] | |
Broca's area is a region of the brain with functions linked to speech production.
The production of language has been linked to the Broca’s area since Paul Pierre Broca reported impairments in two patients. They had lost the ability to speak after injury to the posterior inferior frontal gyrus of the brain.[1] 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.[1] 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.[2]
Anatomy and connectivity
Broca's area is often identified by visual inspection of the topography of the brain either by macrostructural landmarks such as sulci or by the specification of coordinates in a particular reference space. The currently used Talairach and Tournoux atlas projects Brodmann's cytoarchitectonic map on to a template brain. Because Brodmann's parcelation was based on subjective visual inspection of cytoarchitectonic borders and also Brodmann analyzed only one hemisphere of one brain, the result is imprecise. Further, because of considerable variability across brains in terms of shape, size, and position relative to sulcal and gyral structure, a resulting localization precision is limited.[3]
Nevertheless, Broca’s area in the left hemisphere and its homologue in the right hemisphere are designations usually used to refer to pars triangularis (PTr) and pars opercularis (POp) of the inferior frontal gyrus. The PTr and POp are defined by structural landmarks that only probabilistically divide the inferior frontal gyrus into anterior and posterior cytoarchitectonic areas of 45 and 44, respectively, by Brodmann’s classification scheme.[4]
Area 45 receives more afferent connections from prefrontal cortex, the superior temporal gyrus, and the superior temporal sulcus, compared to area 44, which tends to receive more afferent connections from motor, somatosensory, and inferior parietal regions.[4]
The differences between area 45 and 44 in cytoarchitecture and in connectivity suggest that these areas might perform different functions. Indeed, recent neuroimaging studies have shown that the PTr and Pop, coressponding to areas 45 and 44, respectively, play different functional roles in the human with respect to language comprehension and action recognition/understanding.[4]
Broca's area revisited
In a recent study, the preserved brains of both Leborgne and Lelong (patients of Paul Pierre Broca) were reinspected using high-resolution volumetric MRI. The purpose of this study was to scan the brains in three dimensions and to identify the extent of both cortical and subcortical lesions in more detail. The study also sought to locate the exact site of the lesion in the frontal lobe in relation to what is now called Broca's area with the extent of subcortical involvement.[1]
Broca's patients
Leborgne
Leborgne was a patient of Paul Pierre Broca. He was unable to produce any words or phrases. The only word he could repetitively produce was 'tan'. After his death, a lesion was discovered on the surface of the left frontal lobe.
Lelong
Lelong was another patient of Paul Pierre Broca. He also exhibited reduced productive speech. He could only say five words, 'yes,' 'no,' 'three,' 'always,' and 'lelo' (a mispronunciation of his own name). At autopsy, a lesion was also found in the same region of lateral frontal lobe as in Leborgne. These two cases led Paul Pierre Broca to believe that speech was localized to this particular area.
MRI findings
Examination of the brains of Paul Pierre Broca's two historic patients with high resolution MRI has produced several interesting findings. First, the MRI findings suggest that other areas besides Broca's area may also have contributed to the patients' reduced productive speech. This finding is significant because it has been found that though lesions to Broca's area alone can possibly cause temporary speech disruption, they do not result in severe speech arrest. Therefore, there is a possibility that the aphasia denoted by Broca as an absence of productive speech also could have been influenced by the lesions in the other region. Another interesting finding is that the lesion, which was once considered to be critical for speech by Broca, is not precisely the same region as what is now known as Broca's area. This study provides further evidence that language and cognition are far more complicated than once thought and involve various networks of brain regions.
Speaking without Broca’s area
The essential role of the Broca's area in speech production has been questioned since it can be destroyed while leaving language nearly intact. In one case of a computer engineer a slow growing glioma was removed. The tumor and the surgery destroyed the left inferior and middle frontal gyrus, the head of the caudate nucleus, the anterior limb of the internal capsule and the anterior insula. However there were minimal language problems three months after removal and the individual returned to his professional work. These minor problems include the inability to create syntactically complex sentences with including more than two subjects, multiple causal conjunctions or reported speech. These were explained by researchers as due to working memory problems. They also attributed his lack of problems to extensive compensatory mechanisms enabled by neural plasticity in the nearby cerebral cortex and a shift of some functions to the homologous area in the right hemisphere.[2]
Functions
Language comprehension
For a long time, it was assumed that the role of Broca's area was more devoted to language production than language comprehension. However, recent evidence demonstrates that Broca's area also plays a significant role in language comprehension. Patients with lesions in Broca's area who exhibit agrammatical speech production also show inability to use syntactic information to determine the meaning of sentences.[5] Also, a number of neuroimaging studies have implicated an involvement of Broca's area, particularly of the pars opercularis of the left inferior frontal gyrus, during the processing of complex sentences.[6] Further, it has recently been found in functional magnetic resonance imaging (fMRI) experiments involving highly ambiguous sentences result in a more activated inferior frontal gyrus.[4] Therefore, the activity level in the inferior frontal gyrus and the level of lexical ambiguity are directly proportional to each other, because of the increased retrieval demands associated with highly ambiguous content.
Action recognition and production
Recent experiments have indicated that Broca's area is involved in various cognitive and perceptual tasks. One important contribution of Brodmann's area 44 is also found in the motor-related processes. Observation of meaningful hand shadows resembling moving animals activates frontal language area, demonstrating that Broca's area indeed plays a role in interpreting action of others.[7] An activation of BA 44 was also reported during execution of grasping and manipulation.[8]
Speech-associated gestures
It has been speculated that because speech-associated gestures could possibly reduce lexical or sentential ambiguity, comprehension should improve in the presence of speech-associated gestures. As a result of improved comprehension, the involvement of Broca's area should be reduced.[4]
Many neuroimaging studies have also shown activation of Broca's area when representing meaningful arm gestures. A recent study has shown evidence that word and gesture are related at the level of translation of particular gesture aspects such as goal and intention.[9] This finding that aspects of gestures are translated in words within Broca's area also explains language development in terms of evolution. Indeed, many authors have proposed that speech evolved from a primitive communication that arose from gestures.[7],[10] (see Evolution of Language below)
Aphasia
Aphasia is an acquired language disorder affecting all modalities such as writing, reading, speaking, and listening and results from brain damage. It is often a chronic condition that creates changes in all areas of one’s life.[11]
Broca's aphasia vs. other aphasias
Patients with Broca's aphasia are individuals who know "what they want to say, they just cannot get it out." [11] They are typically able to understand what is being said to them, but unable to fluently speak. This is also known as non-fluent aphasia. Some of other symptoms may include problems with fluency, articulation, word-finding, word repetition, and producing and comprehending complex grammatical sentences, both orally and in writing.[1] These characteristics distinguish them from other individuals with other types of aphasia. Other aphasia types may have more difficulty understanding what is said to them. They may also struggle more with reading and writing than do individuals with Broca’s aphasia. While the individuals with Broca’s aphasia also have a good ability to self-monitor their language output, other types of aphasia may be more unaware of their language performance. Also, site of lesion (brain damaged area) differs between the different aphasias.
| Type of Aphasia | Repetition | Naming | Auditory Comprehension | Fluency |
|---|---|---|---|---|
| Broca's | Mod-severe | Mod-severe | Mild difficulty | Non-fluent, effortful, slow |
| Wernicke's | Mild-severe | Mild-severe | Defective | Fluent paraphasic |
| Conduction | Poor | Poor | Relatively good | Fluent |
| Mixed Transcortical | Moderate | Poor | Poor | Non-fluent |
| Transcortical Motor | Good | Mild-severe | Mild | Non-fluent |
| Transcortical Sensory | Good | Mod-severe | Poor | Fluent |
| Global | Poor | Poor | Poor | Non-fluent |
| Anomic | Mild | Mod-severe | Mild | Fluent |
Evolution of language
Several models have been proposed to explain the origin of human language. Human language is thought to have evolved as the “evolutionary refinement of an implicit communication system already present in lower primates, based on a set of hand/mouth goal-directed action representations.”[7] The recent finding that Broca’s area is involved during meaningful action observation supports this idea. It was hypothesized that Broca’s area precursor was involved in generating action meanings by interpreting motor sequences in terms of goal. It was further argued that this ability might have been generalized during the evolution that gave this area the capability to deal with meanings. The activated frontal language areas when observing meaningful hand shadows resembling moving animals provides evidence that the human language may have evolved from neural substrates already involved in gestural recognition. Therefore, the study has demonstrated human Broca’s area as the motor center for speech, assembling and decoding communicative gestures. Consistent with this idea is that the neural substrate that regulated motor control in the common ancestor of apes and humans was most likely modified to enhance cognitive and linguistic ability.[10]
Another recent finding has showed significant areas of activation in subcortical and neocortical areas during the production of communicative manual gestures and vocal signals in chimpanzees.[12] Further, the data indicating that chimpanzees intentionally produce manual gestures as well as vocal signals to communicate with humans suggests that the precursors to human language are present at both the behavioral and neuronanatomical levels.
Additional images
See also
References
- ↑ 1.0 1.1 1.2 1.3 N. F. Dronkers, O. Plaisant, M. T. Iba-Zizen, and E. A. Cabanis (2007). Paul Broca's Historic Cases: High Resolution MR Imaging of the Brains of Leborgne and Lelong. Brain 130.
- ↑ 2.0 2.1 Plaza M, Gatignol P, Leroy M, Duffau H. (2009). Speaking without Broca's area after tumor resection. Neurocase.9:1-17. PMID 19274574
- ↑ Yosef Grodzinsky and Andrea Santi (2002). The Battle for Broca's Region. Trends in Cognitive Sciences 12 (12).
- ↑ 4.0 4.1 4.2 4.3 4.4 Jeremy I. Skipper, Susan Goldin-Meadow, Howard C. Nusbaum, and Steven L. Small (2007). Speech-Associated Gestures, Broca's Area, and the Human Mirror System. Brain and Language 101.
- ↑ David Caplan (2006). Why is Broca's Area Involved in Syntax?. Cortex 42.
- ↑ Tanja Crewe, Ina Bornkessel, Stefan Zysset, Richard Wiese, D. Yves von Cramon, and Matthias Schlesewksy (2005). The Emergence of the Unmarked: A New Perspective on the Language-Specific Function of Broca's Area. Human Brain Mapping 26.
- ↑ 7.0 7.1 7.2 Luciano Fadiga, Laila Craighero, Maddalena Fabbri Destro, Livio Finos, Nathalie Cotilon-Williams, Andrew T. Smith, and Umberto Castiello (2006). Language in Shadow. Social Neuroscience 1 (2).
- ↑ Luciano Fadiga and Laila Craighero (2006). Hand Actions and Speech Representation In Broca's Area. Cortex 42.
- ↑ Maurizio Gentilucci, Paolo Bernardis, Girolamo Crisi, and Riccardo Dalla Volta (2006). Repetitive Transcranial Magnetic Stimulation of Broca's Area Affects Verbal Responses to Gesture Observation. Journal of Cognitive Neuroscience 18 (7).
- ↑ 10.0 10.1 Philip Lieberman (2002). On the Nature and Evolution of the Neural Bases of Human Language. Yearbook of Physical Anthropology 45.
- ↑ 11.0 11.1 11.2 (2006). What is Aphasia. Atlanta Aphasia Association. URL accessed on 2008-12-01.
- ↑ Jared P. Taglialatela, Jamie L. Russell, Jennifer A. Schaeffer, and William D. Hopkins (2008). Communicative Signaling Activates 'Broca's' Homolog in Chimpanzees. Current Biology 18.
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