The inferior frontal gyrus (IFG; also gyrus frontalis inferior) is the lowest positioned gyrus of the frontal gyri, of the

frontal lobe 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 (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a Sulcus (neur ...

, and is part of the

prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. It is the association cortex in the frontal lobe. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, ...

. 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. The inferior frontal gyrus contains

Broca's area Broca's area, or the Broca area (, also , ), is a region in the frontal lobe of the dominant Cerebral hemisphere, hemisphere, usually the left, of the Human brain, brain with functions linked to speech production. Language processing in the brai ...

, which is involved in language processing and speech production.

Structure

The inferior frontal gyrus is highly convoluted and has three cytoarchitecturally diverse regions. 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. The ascending ramus separates the opercular and triangular parts. The anterior (horizontal) ramus separates the triangular and orbital parts. * Opercular part of inferior frontal gyrus (pars opercularis), (cortex posterior to the ascending ramus of the lateral sulcus), is the part of frontal lobe that overlies the

insular cortex The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal lobe, parietal and frontal lobes) within each brain hemisphere ...

and may be associated with recognizing a tone of voice in spoken native languages. This expands on previous work indicating that comprehension of inflectional

morpheme A morpheme is any of the smallest meaningful constituents within a linguistic expression and particularly within a word. Many words are themselves standalone morphemes, while other words contain multiple morphemes; in linguistic terminology, this ...

processing is associated with the inferior frontal gyrus. * Triangular part of inferior frontal gyrus (pars triangularis), (cortex between the ascending ramus and the horizontal ramus of the lateral sulcus). It may be associated with the ability to translate from a secondary or tertiary language back to one's native language. *

Orbital part of inferior frontal gyrus The orbital part of inferior frontal gyrus also known as the pars orbitalis is the orbital part of the inferior frontal gyrus. In humans, this region is bordered by the triangular part of the inferior frontal gyrus (pars triangularis) and, su ...

(pars orbitalis) (cortex inferior and anterior to the horizontal ramus of the lateral sulcus) Cytoarchitecturally the opercular part of the inferior frontal gyrus is known as

Brodmann area 44 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. This area is also known as pars opercularis (of the inferior frontal gyr ...

(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

Function

The inferior frontal gyrus has a number of functions including the processing of speech and language in

. Neural circuitry has been shown to connect different sites of stimulus to other regions of response including other subdivisions and also other frontal gyri.

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 The premotor cortex is an area of the motor cortex lying within the frontal lobe of the brain just anterior to the primary motor cortex. It occupies part of Brodmann's area 6. It has been studied mainly in primates, including monkeys and human ...

, 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 The vocal tract is the cavity in human bodies and in animals where the sound produced at the sound source (larynx in mammals; syrinx in birds) is filtered. In birds, it consists of the trachea, the syrinx, the oral cavity, the upper part of t ...

moves to produce syllables. The pars opercularis acts indirectly through the

motor cortex The motor cortex is the region of the cerebral cortex involved in the planning, motor control, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...

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. 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.

Language comprehension and production

Most language processing takes place in

usually in the left hemisphere. Damage to this region often results in a type of non-fluent

aphasia Aphasia, also known as dysphasia, is an impairment in a person's ability to comprehend or formulate language because of dysfunction in specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine, but aph ...

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 Transcranial magnetic stimulation (TMS) is a noninvasive neurostimulation technique in which a changing magnetic field is used to induce an electric current in a targeted area of the brain through electromagnetic induction. A device called a st ...

to the left IFG has been shown to release such inhibition, increasing the ability to learn from undesirable information. The right opercular part of the IFG, (BA44) has been implicated in go/no go tasks. 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. 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.

Additional images

File:Inferior frontal gyrus coronal sections.gif, Inferior frontal gyrus highlighted in green on coronal T1 MRI images File:Inferior frontal gyrus sagittal sections.gif, Inferior frontal gyrus highlighted in green on sagittal T1 MRI images File:Inferior frontal gyrus transversal sections.gif, Inferior frontal gyrus highlighted in green on transversal T1 MRI images

References

External links

* {{DEFAULTSORT:Inferior Frontal Gyrus Gyri Frontal lobe