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

gyrus In neuroanatomy, a gyrus (pl. gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; sg. ''sulcus''). Gyri and sulci create the folded appearance of the brain in humans and other ma ...

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, and ...

, 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 groove betwe ...

, 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, BA46, ...

. Its superior border is the

inferior frontal sulcus The inferior frontal sulcus is a sulcus between the middle frontal gyrus and the inferior frontal gyrus. See also * Superior frontal sulcus Additional images File:Inferior frontal sulcus animation small.gif, Animation. Inferior frontal sulcus ...

(which divides it from the

middle frontal gyrus The middle frontal gyrus makes up about one-third of the frontal lobe of the human brain. (A ''gyrus'' is one of the prominent "bumps" or "ridges" on the surface of the human brain.) The middle frontal gyrus, like the inferior frontal gyrus an ...

), its inferior border is the

lateral sulcus In neuroanatomy, the lateral sulcus (also called Sylvian fissure, after Franciscus Sylvius, or lateral fissure) is one of the most prominent features of the human brain. The lateral sulcus is a deep fissure in each hemisphere that separates the ...

(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 lat ...

) and its posterior border is the inferior precentral sulcus. Above it is the

, behind it is the

precentral gyrus The precentral gyrus is a prominent gyrus on the surface of the posterior frontal lobe of the brain. It is the site of the primary motor cortex that in humans is cytoarchitecturally defined as Brodmann area 4. Structure The precentral gyrus l ...

. 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 Language processing refers to the way humans use words to communicate ideas and feelings, and how such communications are processed and understood. Language processing is considered to be a uniquely human ability that is not produced with the sa ...

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 vo ...

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

. 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 and frontal lobes) within each hemisphere of the mammalian bra ...

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 defin ...

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 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, surr ...

(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 gyru ...

(BA44). The triangular part of the inferior frontal gyrus is known as

Brodmann area 45 Brodmann area 45 (BA45), is part of the Frontal lobe, frontal Cerebral cortex, cortex in the human brain. It is situated on the lateral surface, inferior to Brodmann area 9, BA9 and adjacent to Brodmann area 46, BA46. This area in humans occupies ...

(BA45), and the orbital part of the inferior frontal gyrus is known as

Brodmann area 47 Brodmann is a German surname. Notable people with the surname include: *Ines Brodmann (birth date unknown), Swiss orienteer *Korbinian Brodmann (1868–1918), German neurologist *Mario Brodmann (born 1966), Swiss former ice hockey forward *René Br ...

. 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 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 humans. ...

, 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 (biology), syrinx in birds) is filtered. In birds it consists of the Vertebrate trachea, trachea, the Syrinx (bio ...

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

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

to control the motor aspect of

, and codes motor programs for this system, while the

auditory cortex The auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to ...

(via the

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

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 th ...

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 apha ...

. 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 form of brain stimulation in which a changing magnetic field is used to induce an electric current at a specific area of the brain through electromagnetic induction. An electric pulse gener ...

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 Transcranial direct current stimulation (tDCS) is a form of neuromodulation that uses constant, low direct current delivered via electrodes on the head. It was originally developed to help patients with brain injuries or neuropsychiatric conditio ...

(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