Inferior frontal gyrus

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Inferior frontal gyrus
FrontalCaptsLateral.png
Inferior frontal gyrus of the human brain, gyrus frontalis inferior.
Gray726 inferior frontal gyrus.png
Lateral surface of left hemisphere viewed from the side. Inferior frontal gyrus shown in yellow.
Details
Part of Frontal lobe
PartsPars opercularis, Pars triangularis, Pars orbitalis
Artery Middle cerebral
Identifiers
Latin gyrus frontalis inferior
NeuroNames 85
NeuroLex ID birnlex_873
TA98 A14.1.09.113
A15.2.07.058
TA2 5447
FMA 61860
Anatomical terms of neuroanatomy

The inferior frontal gyrus (IFG), (gyrus frontalis inferior), is the lowest positioned gyrus of the frontal gyri, of the frontal lobe, and is part of the prefrontal cortex.

Contents

Its superior border is the inferior frontal sulcus (which divides it from the middle frontal gyrus), its inferior border is the lateral sulcus (which divides it from the superior temporal gyrus) and its posterior border is the inferior precentral sulcus. Above it is the middle frontal gyrus, behind it is the precentral gyrus. [1]

The inferior frontal gyrus contains Broca's area, which is involved in language processing and speech production.

Structure

The inferior frontal gyrus is highly convoluted and has three cytoarchitecturally diverse regions. [2] The three subdivisions are an opercular part, a triangular part, and an orbital part. These divisions are marked by two rami arising from the lateral sulcus. [3] The ascending ramus separates the opercular and triangular parts. [4] The anterior (horizontal) ramus separates the triangular and orbital parts. [5]

Cytoarchitecturally the opercular part of the inferior frontal gyrus is known as Brodmann area 44 (BA44). The triangular part of the inferior frontal gyrus is known as Brodmann area 45 (BA45), and the orbital part of the inferior frontal gyrus is known as Brodmann area 47. The opercular part and the triangular part (BA44 and BA45) make up Broca's area.

Function

The inferior frontal gyrus has a number of functions including the processing of speech and language in Broca's area. Neural circuitry has been shown to connect different sites of stimulus to other regions of response including other subdivisions and also other frontal gyri. [2]

Language processing

The left opercular part of the inferior frontal gyrus is a part of the articulatory network involved in motor syllable programs. The articulatory network also contains the premotor cortex, and the anterior insula. These areas are interrelated but have specific functions in speech comprehension and production. The articulatory network acts mostly when the vocal tract moves to produce syllables. The pars opercularis acts indirectly through the motor cortex to control the motor aspect of speech production, and codes motor programs for this system, while the auditory cortex (via the temporoparietal junction in the lateral sulcus (Sylvian fissure) houses a series of sensory targets. Together, these areas function as a sensory-motor loop for syllable information coding.[ citation needed ]

In a study conducted comparing phonological and arithmetic processing and the involvement of different sections of the inferior frontal gyrus and angular gyrus, cortical activation for phonology, subtraction, and multiplication tasks was compared. The predetermined language-calculation network was limited to the left inferior frontal gyrus, angular gyrus, superior parietal lobule, and the horizontal portion of the intraparietal sulcus. The results were significant to support that there was a pattern of left lateralization for each of these tasks all activating the Perisylvian fissure network, with some general localized areas for phonology and arithmetic. It was supported that phonology activated the pars opercularis (BA44), and anterior angular gyrus, multiplication mainly implicated the pars triangularis (BA45), and the posterior angular gyrus. These systems are activated through similar neuronal processes but independently placed along the network.[ citation needed ]

Language comprehension and production

Most language processing takes place in Broca's area usually in the left hemisphere. [9] Damage to this region often results in a type of non-fluent aphasia known as Broca's aphasia. Broca's area is made up of the pars opercularis and the pars triangularis, both of which contribute to verbal fluency, but each has its own specific contribution. The pars opercularis (BA44) is involved in language production and phonological processing due to its connections with motor areas of the mouth and tongue. The pars triangularis (BA45) is involved in semantic processing. Characteristics of Broca's aphasia include agrammatic speech, relatively good language comprehension, poor repetition, and difficulty speaking mostly uttering short sentences made up mostly of nouns. The left IFG has also been suggested to play a role in inhibitory processes, including the tendency to inhibit learning from undesirable information. For example, transcranial magnetic stimulation to the left IFG has been shown to release such inhibition, increasing the ability to learn from undesirable information. [10]

The right opercular part of the IFG, (BA44) has been implicated in go/no go tasks. [11] In these tasks, the participant encounters a preliminary task (for instance repeatedly pressing a button), and then must halt this task whenever a "no go" signal is presented, ultimately measuring a level of impulse control through inhibition of a prepotent response. It seems that the same area is also implicated in risk aversion: a study found that higher risk aversion correlated with higher activity at IFG. [12] This might be explained as an inhibition signal to accept a risky option. Disruption of activity of this area with transcranial direct-current stimulation (tDCS) leads to change in risk attitudes, as behaviorally demonstrated by choices over risky outcomes. [13] [14]

Additional images

Related Research Articles

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<span class="mw-page-title-main">Broca's area</span> Speech production region in the dominant hemisphere of the hominid brain

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Articles related to anatomy include:

<span class="mw-page-title-main">Cingulate cortex</span> Part of the brain within the cerebral cortex

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<span class="mw-page-title-main">Brodmann area</span> Region of the brain

A Brodmann area is a region of the cerebral cortex, in the human or other primate brain, defined by its cytoarchitecture, or histological structure and organization of cells. The concept was first introduced by the German anatomist Korbinian Brodmann in the early 20th century. Brodmann mapped the human brain based on the varied cellular structure across the cortex and identified 52 distinct regions, which he numbered 1 to 52. These regions, or Brodmann areas, correspond with diverse functions including sensation, motor control, and cognition.

<span class="mw-page-title-main">Frontal lobe</span> Part of the brain

The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere. It is parted from the parietal lobe by a groove between tissues called the central sulcus and from the temporal lobe by a deeper groove called the lateral sulcus. The most anterior rounded part of the frontal lobe is known as the frontal pole, one of the three poles of the cerebrum.

<span class="mw-page-title-main">Brodmann area 6</span>

Brodmann area 6 (BA6) is part of the frontal cortex in the human brain. Situated just anterior to the primary motor cortex (BA4), it is composed of the premotor cortex and, medially, the supplementary motor area (SMA). This large area of the frontal cortex is believed to play a role in planning complex, coordinated movements.

<span class="mw-page-title-main">Brodmann area 44</span> Brain area

Brodmann area 44, or BA44, 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.

<span class="mw-page-title-main">Brodmann area 45</span> Brain area

Brodmann area 45 (BA45), is part of the frontal cortex in the human brain. It is situated on the lateral surface, inferior to BA9 and adjacent to BA46.

Expressive language disorder is one of the "specific developmental disorders of speech and language" recognised by the tenth edition of the International Classification of Diseases (ICD-10). As of the eleventh edition, it is considered to be covered by the various categories of developmental language disorder. Transition to the ICD-11 will take place at a different time in different countries.

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<span class="mw-page-title-main">Middle cerebral artery</span> Paired artery that supplies blood to the cerebrum

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<span class="mw-page-title-main">Orbital part of inferior frontal gyrus</span>

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References

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