View source for Biology:Inferior frontal gyrus

{{Infobox brain
| Name            = Inferior frontal gyrus
| Latin           = gyrus frontalis inferior
| Image           = FrontalCaptsLateral.png
| Caption         = Inferior frontal gyrus of the human brain, ''gyrus frontalis inferior''.
| Image2          = Gray726 inferior frontal gyrus.png
| Caption2        = Lateral surface of left [[Biology:Cerebral hemisphere|hemisphere]] viewed from the side. Inferior frontal gyrus shown in yellow.
| IsPartOf        = [[Biology:Frontal lobe|Frontal lobe]]
| Components      = Pars opercularis, Pars triangularis, [[Biology:Orbital part of inferior frontal gyrus|Pars orbitalis]]
| Artery          = Middle cerebral
| Vein            =
}}
The '''inferior frontal gyrus''' '''(IFG)''', '''(gyrus frontalis inferior)''', is the lowest positioned [[Biology:Gyrus|gyrus]] of the [[Biology:Frontal gyri|frontal gyri]], of the [[Biology:Frontal lobe|frontal lobe]], and is part of the [[Biology:Prefrontal cortex|prefrontal cortex]].

Its superior border is the [[Biology:Inferior frontal sulcus|inferior frontal sulcus]] (which divides it from the [[Biology:Middle frontal gyrus|middle frontal gyrus]]), its inferior border is the [[Biology:Lateral sulcus|lateral sulcus]] (which divides it from the [[Biology:Superior temporal gyrus|superior temporal gyrus]]) and its posterior border is the [[Biology:Precentral sulcus|inferior precentral sulcus]]. Above it is the [[Biology:Middle frontal gyrus|middle frontal gyrus]], behind it is the [[Biology:Precentral gyrus|precentral gyrus]].<ref>{{Citation|last=Nolte |year=2002| title=The Human Brain | isbn=978-0-323-01320-8}} photos on p526 & p.546</ref>

The inferior frontal gyrus contains [[Biology:Broca's area|Broca's area]], which is involved in [[Biology:Language processing in the brain|language processing]] and [[Engineering:Speech production|speech production]].

==Structure==
The inferior frontal gyrus is highly convoluted and has three [[Biology:Cytoarchitecture|cytoarchitecturally]] diverse regions.<ref name="Greenlee">{{cite journal |last1=Greenlee|display-authors=0 |first1=JD |title=Functional connections within the human inferior frontal gyrus. |journal=The Journal of Comparative Neurology |date=1 August 2007 |volume=503 |issue=4 |pages=550–9 |doi=10.1002/cne.21405 |pmid=17534935|s2cid=5685566 }}</ref> The three subdivisions are an opercular part, a triangular part, and an orbital part. These divisions are marked by two rami arising from the [[Biology:Lateral sulcus|lateral sulcus]].<ref name="Dict">{{cite web |title=anterior ramus of lateral cerebral sulcus |url=https://medical-dictionary.thefreedictionary.com/anterior+ramus+of+lateral+cerebral+sulcus |website=TheFreeDictionary.com}}</ref> The ascending ramus separates the opercular and triangular parts.<ref name="Gaillard">{{cite web |last1=Gaillard |first1=Frank |title=Ascending ramus of the lateral sulcus {{!}} Radiology Reference Article {{!}} Radiopaedia.org |url=https://radiopaedia.org/articles/ascending-ramus-of-the-lateral-sulcus?lang=gb |website=Radiopaedia}}</ref> The anterior (horizontal) ramus separates the triangular and orbital parts.<ref name="Radiopedia">{{cite web |last1=Gaillard |first1=Frank |title=Anterior ramus of the lateral sulcus {{!}} Radiology Reference Article {{!}} Radiopaedia.org |url=https://radiopaedia.org/articles/anterior-ramus-of-the-lateral-sulcus |website=Radiopaedia}}</ref>

* '''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 [[Biology:Insular cortex|insular cortex]] and may be associated with recognizing a tone of voice in spoken native languages.<ref name="Schrem">{{cite journal |last1=Schremm|display-authors=0 |first1=A |title=Cortical thickness of planum temporale and pars opercularis in native language tone processing. |journal=Brain and Language | date=January 2018 |volume=176 | pages=42–47 | doi=10.1016/j.bandl.2017.12.001 |pmid=29223785 |doi-access=free }} </ref> This expands on previous work<ref name="Tyler">{{cite journal |last1=Tyler|display-authors=0 |first1=LK |title=Temporal and frontal systems in speech comprehension: An fMRI study of past tense processing |journal=Neuropsychologia |date=2005 |volume=43 |issue=13 |pages=1963–1974 |doi=10.1016/j.neuropsychologia.2005.03.008|pmid=16168736 |s2cid=16112201 }} </ref> indicating that comprehension of [[Social:Inflection|inflectional]] [[Social:Morpheme|morpheme]] 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.<ref name="Elmer">{{cite journal |last1=Elmer|first1=Stefan |title=Broca Pars Triangularis Constitutes a "Hub" of the Language-Control Network during Simultaneous Language Translation |journal=Frontiers in Human Neuroscience |date=29 November 2016 |volume=10 |page=491 |doi=10.3389/fnhum.2016.00491 |pmid=27746729 |pmc=5040713 |doi-access=free }} </ref> 
* [[Biology:Orbital part of inferior frontal gyrus|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 [[Biology:Brodmann area 44|Brodmann area 44]] (BA44). The triangular part of the inferior frontal gyrus is known as [[Biology:Brodmann area 45|Brodmann area 45]] (BA45), and the orbital part of the inferior frontal gyrus is known as
[[Biology:Brodmann area 47|Brodmann area 47]]. The opercular part and the triangular part (BA44 and BA45) make up [[Biology:Broca's area|Broca's area]].

== Function ==
The inferior frontal gyrus has a number of functions including the [[Biology:Language processing in the brain|processing of speech and language]] in [[Biology:Broca's area|Broca's area]]. [[Neural circuit]]ry has been shown to connect different sites of stimulus to other regions of response including other subdivisions and also other frontal gyri.<ref name="Greenlee"/>

===Language processing===
The left opercular part of the inferior frontal gyrus is a part of the [[Biology:Two-streams hypothesis#Two auditory systems|articulatory network]] involved in motor syllable programs. The articulatory network also contains the [[Biology:Premotor cortex|premotor cortex]], and the anterior [[Biology:Insular cortex|insula]]. These areas are interrelated but have specific functions in speech comprehension and production. The articulatory network acts mostly when the [[Medicine:Vocal tract|vocal tract]] moves to produce syllables. The pars opercularis acts indirectly through the [[Biology:Motor cortex|motor cortex]] to control the motor aspect of [[Engineering:Speech production|speech production]], and codes motor programs for this system, while the [[Biology:Auditory cortex|auditory cortex]] (via the [[Biology:Temporoparietal junction|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|date=December 2018}}

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|date=December 2018}}

===Language comprehension and production===
Most language processing takes place in [[Biology:Broca's area|Broca's area]] usually in the left hemisphere.<ref>The "dominant inferior frontal convolution" —{{Citation|last=Fauci| first= et.al, eds.| year=1998 |title=Harrison's Principles of Internal Medicine, 14th Edition, Companion Handbook| isbn=978-0-07-021530-6}}. p.1055</ref> Damage to this region often results in a type of non-fluent [[Medicine:Aphasia|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, [[Physics:Transcranial magnetic stimulation|transcranial magnetic stimulation]] to the left IFG has been shown to release such inhibition, increasing the ability to learn from undesirable information.<ref>Sharot, T., Kanai, R., Marston, D., Korn, C. W., Rees, G. & Dolan, R.J. (2012) Selectively Altering Belief Formation in the Human Brain. Proceedings of the National Academy of Sciences, 109 (42), 17058–17062.</ref>

The right opercular part of the IFG, (BA44) has been implicated in go/no go tasks.<ref>{{cite journal |doi= 10.1016/j.tics.2004.02.010 |journal= Trends Cogn Sci |year=2004 |volume=8 |issue= 4 |pages=170–177 |title= Inhibition and the right inferior frontal cortex |vauthors=Aron AR, Robbins TW, Poldrack RA |pmid= 15050513|s2cid= 19332756 }}</ref> 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.<ref name="pmid19812332">{{Cite journal  | last1 = Christopoulos | first1 = GI. | last2 = Tobler | first2 = PN. | last3 = Bossaerts | first3 = P. | last4 = Dolan | first4 = RJ. | last5 = Schultz | first5 = W. | title = Neural correlates of value, risk, and risk aversion contributing to decision making under risk | journal = J Neurosci | volume = 29 | issue = 40 | pages = 12574–83 |date=Oct 2009 | doi = 10.1523/JNEUROSCI.2614-09.2009 | pmid = 19812332 | pmc=2794196}}</ref> This might be explained as an inhibition signal to accept a risky option. Disruption of activity of this area with [[Biology:Transcranial direct-current stimulation|transcranial direct-current stimulation]] (tDCS) leads to change in risk attitudes, as behaviorally demonstrated by choices over risky outcomes.<ref>{{cite journal |doi= 10.1523/JNEUROSCI.0804-06.2006 |journal= J Neurosci  |year=2006 |volume=26 |issue= 24 |pages=6469–6472
| title = Disruption of right prefrontal cortex by low-frequency repetitive transcranial magnetic stimulation induces risk-taking behavior. |vauthors=Knoch D, Gianotti LR, Pascual-Leone A, Treyer V, Regard M, Hohmann M, Brugger P |pmid= 16775134|pmc= 6674035 |url= http://boris.unibe.ch/61185/1/6469.full.pdf |doi-access= free }}</ref><ref>{{cite journal |doi= 10.1523/JNEUROSCI.0314-07.2007 |journal= J Neurosci  |year=2007 |volume=27 |issue= 23 |pages=6212–6218 |title= Activation of prefrontal cortex by transcranial direct current stimulation reduces appetite for risk during ambiguous decision making |vauthors=Fecteau S, Pascual-Leone A, Zald DH, Liguori P, Théoret H, Boggio PS, Fregni F |pmid= 17553993|pmc= 6672163 |doi-access= free }}</ref>

==Additional images==
<gallery>
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
</gallery>

==References==
<references/>

{{DEFAULTSORT:Inferior Frontal Gyrus}}
[[Category:Gyri]]
[[Category:Frontal lobe]]

{{Sourceattribution|Inferior frontal gyrus}}