The inferior frontal gyrus is the lowest of the three horizontal ridges on the outer side of each frontal lobe, just above the lateral (Sylvian) fissure; it is part of the prefrontal cortex. [1]
The model has one shape per side for the whole gyrus. Its three parts (pars opercularis, pars triangularis and pars orbitalis) are described below in text only: they are not separate shapes, so they cannot be lit on their own. [2][1]
The 3D brain needs JavaScript. The text below still says where the inferior frontal gyrus is and what it does.
Slice
Opens cut by a front (coronal) slice through the inferior frontal gyrus. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Areas on this gyrus, each on its own page: Broca’s area.
Takes part in: speech, reading — see every part of each lit together.
Where it is
The outer surface of the frontal lobe has four gyri: the precentral gyrus, directly in front of the central sulcus, and three horizontal ones ahead of it, the superior, middle and inferior frontal gyri. [3]
Above it the inferior frontal sulcus divides it from the middle frontal gyrus; below it the lateral sulcus divides it from the superior temporal gyrus; behind it, past the inferior precentral sulcus, is the precentral gyrus. [1]
Two branches (rami) of the lateral sulcus cut it into three parts: the ascending ramus separates the opercular and triangular parts, and the anterior (horizontal) ramus separates the triangular and orbital parts. [1]
From back to front: the pars opercularis (Brodmann area 44), which overlies the insula; the pars triangularis (area 45); and the pars orbitalis (area 47), below and in front of the horizontal ramus. [1]
What it does
The pars opercularis and pars triangularis (areas 44 and 45) make up Broca’s area, which is involved in language processing and producing speech. [1][4]
The left pars opercularis is part of the articulatory network with the premotor cortex and the front of the insula; it codes the motor programs for syllables and acts on speech through the motor cortex. [1]
The pars opercularis has been associated with recognising tone of voice in one’s native language, and the pars triangularis with translating from a second or third language back into the native one. [1]
Connections
The arcuate fasciculus links Broca’s area with Wernicke’s area, which spans the region between the temporal and parietal lobes. [4]
The frontal aslant tract joins Broca’s area to the superior frontal gyrus, in both directions. [5]
In human diffusion imaging the front of the insula is wired to the inferior frontal gyrus. [6]
Other names
IFG, gyrus frontalis inferior. Its three parts are the opercular, triangular and orbital parts (pars opercularis, pars triangularis, pars orbitalis); the first two together are Broca’s area. [1]
Size
On this model the left inferior frontal gyrus measures about 63 mm front to back, 60 mm top to bottom and 35 mm side to side (the box it fits in, not its volume); the right one is its mirror image. [2]
Centre of the left inferior frontal gyrus compared with the centre of the left middle frontal gyrus: 18 mm lower, 12 mm further from the midline; 22 mm apart in a straight line. [2]
Centre of the left inferior frontal gyrus compared with the centre of the left insula: 20 mm further forward, 9 mm higher, 6 mm further from the midline; 23 mm apart in a straight line. [2]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.