Connections of the Human Orbitofrontal Cortex and Inferior Frontal Gyrus

Abstract

The direct connections of the orbitofrontal cortex (OFC) were traced with diffusion tractography imaging and statistical analysis in 50 humans, to help understand better its roles in emotion and its disorders. The medial OFC and ventromedial prefrontal cortex have direct connections with the pregenual and subgenual parts of the anterior cingulate cortex; all of which are reward-related areas. The lateral OFC (OFClat) and its closely connected right inferior frontal gyrus (rIFG) have direct connections with the supracallosal anterior cingulate cortex; all of which are punishment or nonreward-related areas. The OFClat and rIFG also have direct connections with the right supramarginal gyrus and inferior parietal cortex, and with some premotor cortical areas, which may provide outputs for the OFClat and rIFG. Another key finding is that the ventromedial prefrontal cortex shares with the medial OFC especially strong outputs to the nucleus accumbens and olfactory tubercle, which comprise the ventral striatum, whereas the other regions have more widespread outputs to the striatum. Direct connections of the OFC and IFG were with especially the temporal pole part of the temporal lobe. The left IFG, which includes Broca’s area, has direct connections with the left angular and supramarginal gyri.

Rapid Rule-Based Reward Reversal and the Lateral Orbitofrontal Cortex

“…The orbitofrontal cortex then projects to the anterior cingulate cortex, as shown by anatomical studies in macaques ( Ongür and Price 2000 ; Price 2007 ), and as supported by functional connectivity ( Du et al. 2020b ) and tract-tracing ( Hsu et al. 2020 ) studies in humans.…”

“…An activation was also found bilaterally in the inferior parietal cortex ( Figure 2 , [38–50 44] FWE P < 0.000, k = 14 797), in an area known to be connected to the lateral orbitofrontal cortex and adjoining inferior frontal gyrus ( Hsu et al. 2020 ), and this is considered in the Discussion.…”

“…Second, Figure 2 shows that the activation during reversal is more in the right than the left orbitofrontal cortex and indeed that the activation extends into the right inferior frontal gyrus. It is suggested that this is because the left inferior frontal gyrus areas BA45 and BA44 which include Broca’s area are devoted to language (and especially speech production), whereas on the right without commitment to language, there is the opportunity for an enlarged right lateral orbitofrontal cortex area 12 to expand round the inferior prefrontal convexity and to utilize the inferior frontal gyrus as a route to output to premotor cortical areas for the lateral orbitofrontal cortex ( Rolls 2019b ; Hsu et al. 2020 ; Rolls et al.…”

“…The cingulate cortex is implicated in action-to-reward-outcome learning, with information about actions received in the posterior cingulate cortex from the parietal cortex, and information about outcomes received in the anterior cingulate cortex from the orbitofrontal cortex ( Rolls 2019a ). There is now evidence in humans that the reward-related medial orbitofrontal cortex projects to the pregenual anterior cingulate cortex and that the non-reward-related lateral orbitofrontal cortex and adjoining inferior frontal gyrus project to the supracallosal anterior cingulate cortex ( Hsu et al. 2020 ; Du et al.…”

“…The area of the inferior parietal lobule activated in reward reversal interestingly has direct connections with the lateral orbitofrontal cortex and adjacent inferior frontal gyrus (AAL2 areas IFGorb and IFGtri ( Rolls et al. 2015a )), but not with the medial orbitofrontal cortex ( Hsu et al. 2020 ).…”