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

frontal gyri The frontal gyri are four gyri of the frontal lobe in the brain. These are four horizontally oriented, parallel convolutions, of the frontal lobe. The other main gyrus of the frontal lobe is the precentral gyrus which is vertically oriented, an ...

, of the frontal lobe, 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. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA ...

. 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 The superior temporal gyrus (STG) is one of three (sometimes two) gyri in the temporal lobe of the human brain, which is located laterally to the head, situated somewhat above the external ear. The superior temporal gyrus is bounded by: * the l ...

) 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 hemisphere, usually the left, of the brain with functions linked to speech production. Language processing has been linked to Broca's area since Pier ...

, which is involved in language processing and

speech production Speech production is the process by which thoughts are translated into speech. This includes the selection of words, the organization of relevant grammatical forms, and then the articulation of the resulting sounds by the motor system using the v ...

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

inflectional In linguistic morphology, inflection (or inflexion) is a process of word formation in which a word is modified to express different grammatical categories such as tense, case, voice, aspect, person, number, gender, mood, animacy, and definit ...

morpheme A morpheme is the smallest meaningful Constituent (linguistics), constituent of a linguistic expression. The field of linguistics, linguistic study dedicated to morphemes is called morphology (linguistics), morphology. In English, morphemes are ...

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 (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 (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 circuit A neural circuit is a population of neurons interconnected by synapses to carry out a specific function when activated. Neural circuits interconnect to one another to form large scale brain networks. Biological neural networks have inspired the ...

ry 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, 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 th ...

moves to produce syllables. The pars opercularis acts indirectly through the motor cortex to control the motor aspect of

, and codes motor programs for this system, while the auditory cortex (via the

temporoparietal junction The temporoparietal junction (TPJ) is an area of the brain where the temporal lobe, temporal and parietal lobe, parietal lobes meet, at the posterior end of the lateral sulcus (Sylvian fissure). The TPJ incorporates information from the thalamus a ...

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 is an inability to comprehend or formulate language because of damage to specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine but aphasia due to stroke is estimated to be 0.1–0.4% in ...

known as

Broca's aphasia Expressive aphasia, also known as Broca's aphasia, is a type of aphasia characterized by partial loss of the ability to produce language ( spoken, manual, or written), although comprehension generally remains intact. A person with expressive aphas ...

. 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. 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

{{DEFAULTSORT:Inferior Frontal Gyrus Gyri Frontal lobe