Broca’s area


An anatomical region in the frontal lobe of the dominant hemisphere, usually the left, of the hominid brain with functions linked to speech production.

The deficit in language production from Broca’s area is referred to as Broca’s aphasia, also called expressive aphasia.

Broca’s area is defined as the pars opercularis and pars triangularis of the inferior frontal gyrus, represented in Brodmann’s cytoarchitectonic map as areas 44 and 45 of the dominant hemisphere.

Language function lateralized to the left hemisphere in 96% to 99% of right-handed people and 60% of left-handed people. 

Various pathways connect Broca area to the frontal lobe, basal ganglia, cerebellum, and contralateral hemisphere.

Lesions in the Broca area causes a breakdown between one’s thoughts and one’s language abilities. 

Chronic aphasia implicates an essential role of Broca’s area in various speech and language functions.

MRI studies have identified activation patterns in Broca’s area associated with various language tasks.

Speech functions can shift to nearby areas in the brain, as demonstrated by slow destruction of the Broca’s area by brain tumors.

Broca’s areas are 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.

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 divide the inferior frontal gyrus into anterior and posterior cytoarchitectonic areas of 45 and 44, respectively, by Brodmann’s classification scheme.

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.

The PTr and Pop, corresponding to areas 45 and 44, respectively, play different functional roles in the human with respect to language comprehension and action recognition/understanding.

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.

Neuroimaging studies indicate an involvement of Broca’s area, particularly of the pars opercularis of the left inferior frontal gyrus, during the processing of complex sentences.

Functional magnetic resonance imaging (fMRI) involving highly ambiguous sentences result in a more activated inferior frontal gyrus.

The activity level in the inferior frontal gyrus and the level of lexical ambiguity are directly proportional to each other.

The pars triangularis is responsible for processing cognitive function, and disruption of computations performed in this area leads to an increase in time needed to perform computations.

When the pars opercularis, situated in the posterior part of Broca’s area, is stimulated there was an increase in reaction times in a phonological task.

The anterior part of Broca’s area is responsible for understanding the meaning of words and the posterior part of Broca’s area responsible for understanding how words sound.

Neuroimaging studies show activation of Broca’s area when representing meaningful arm gestures., and when this area is defective, those who use sign language also suffer from language deficits.

Stuttering is seen to be associated with underactivity in Broca’s area.

Aphasia is an acquired language disorder affecting all modalities such as writing, reading, speaking, and listening and results from brain damage.

Patients with expressive aphasia, also known as Broca’s aphasia, are able to comprehend words, and sentences with a simple syntactic structure, but are more or less unable to generate fluent speech.

Patients with expressive aphasia may have other symptoms that may be present problems with fluency, articulation, word-finding, word repetition, and producing and comprehending complex grammatical sentences, both orally and in writing.

Classically, expressive aphasia is the result of injury to Broca’s area.

The relationship between Broca’s area and Broca’s aphasia is not as consistent as once thought, as lesions to Broca’s area alone don’t result in a Broca’s aphasia, nor do Broca’s aphasic patients necessarily have lesions in Broca’s area.

Broca’s area frequently emerges in functional imaging studies of sentence processing, and becomes activated in word-level tasks.

Broca’s area can show activation in such non-linguistic tasks as imagery of motion.

Frontal areas adjacent to Broca’s area are important for working memory in non-linguistic as well as linguistic tasks.

BA45/47 is recruited for selecting or comparing information.

BA9/46 may be more involved in the manipulation of information in working memory.

Broca’s area is a key node in manipulating and forwarding neural information across large-scale cortical networks responsible for key components of speech production.

Lesions to Broca’s area alone can possibly cause temporary speech disruption, they do not result in severe speech arrest.

Absence of productive speech also could be influenced by the lesions in the other regions.

Language and cognition are far more complicated than once thought and involve various networks of brain regions.

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