The Orbitofrontal Cortex and Reward

The primate orbitofrontal cortex contains the secondary taste cortex, in which the reward value of taste is represented. It also contains the secondary and tertiary olfactory cortical areas, in which information about the identity and also about the reward value of odors is represented. The orbitofrontal cortex also receives information about the sight of objects and faces from the temporal lobe cortical visual areas, and neurons in it learn and reverse the visual stimulus to which they respond when the association of the visual stimulus with a primary reinforcing stimulus (such as a taste reward) is reversed. However, the orbitofrontal cortex is involved in representing negative reinforcers (punishers) too, such as aversive taste, and in rapid stimulus–reinforcement association learning for both positive and negative primary reinforcers. In complementary neuroimaging studies in humans it is being found that areas of the orbitofrontal cortex (and connected subgenual cingulate cortex) are activated by pleasant touch, by painful touch, by rewarding and aversive taste, and by odor. Damage to the orbitofrontal cortex in humans can impair the learning and reversal of stimulus– reinforcement associations, and thus the correction of behavioral responses when these are no longer appropriate because previous reinforcement contingencies change. This evidence thus shows that the orbitofrontal cortex is involved in decoding and representing some primary reinforcers such as taste and touch; in learning and reversing associations of visual and other stimuli to these primary reinforcers; and in controlling and correcting reward-related and punishment-related behavior, and thus in emotion.




Figure 1. Schematic diagram showing some of the gustatory, olfactory, visual and somatosensory pathways to the orbitofrontal cortex, and some of the outputs of the orbitofrontal cortex. The secondary taste cortex and the secondary olfactory cortex are within the orbitofrontal cortex. V1, primary visual cortex. V4, visual cortical area V4. Abbreviations: as, arcuate sulcus; cc, corpus callosum; cf, calcarine fissure; cgs, cingulate sulcus; cs, central sulcus; ls, lunate sulcus; ios, inferior occipital sulcus; mos, medial orbital sulcus; os, orbital sulcus; ots, occipito-temporal sulcus; ps, principal sulcus; rhs, rhinal sulcus; sts, superior temporal sulcus; lf, lateral (or Sylvian) fissure (which has been opened to reveal the insula); A, amygdala; INS, insula; T, thalamus; TE (21), inferior temporal visual cortex; TA (22), superior temporal auditory association cortex; TF and TH, parahippocampal cortex; TG, temporal pole cortex; 12, 13, 11, orbitofrontal cortex; 35, perirhinal cortex; 51, olfactory (prepyriform and periamygdaloid) cortex. Most of the forward projections shown in this diagram have corresponding backprojections (Rolls and Treves, 1998).

Edmund T. Rolls
The Orbitofrontal Cortex and Reward
Cereb. Cortex 10: 284-294.

http://cercor.oxfordjournals.org/cgi/content/full/10/3/284

Neurogenesis in adult dentate gyrus: Evidence of mitosis in differentiated granule cells following spatial learning

An increasing body of evidence has been presented to demonstrate the idea that neurogenesis occurs only during development and ends before puberty is erroneous. In adult vertebrate brain, neurogenesis persists throughout life mainly in two discrete regions – the dentate gyrus of the hippocampus (DG) and the olfactory bulb. Neurogenesis has been shown by detection of tagged thymidine analogues which are incorporated into the S phase of the cell cycle, but these
may also detect repaired DNA in post-mitotic neurons and/or an abortive cell cycle. Recent retroviral labelling has shown that neuronal progenitors/neuroblasts divide and produce functional neurons. However, it is unclear whether differentiated granule cells (GC) in the DG can divide and give rise to another GC. We have used three-dimensional (3D) reconstructions of serial ultrathin sections to identify and reconstruct GC, thereby illustrating individual mitotic elements and phases. We report that functional GC with clear synaptic specializations re-enter the cell cycle demonstrating for the first time that newly generated neurons within the DG can arise not only from stem cell precursors, but also from differentiated GC.

Neurogenesis in adult dentate gyrus: Evidence of mitosis in differentiated granule cells following spatial learning
V.Popov, J.J.Rodriguez, H.A.Davies, I.V.Kraev, D.Banks, M.I.Cordero, C.Sandi and M.G.Stewart
18TH NATIONAL MEETING OF THE BRITISH NEUROSCIENCE ASSOCIATION 2005