2008-04-01 notes on the orbitofrontal cortex

Orbitofrontal cortex is activated during breaches of expectation in tasks of visual attention

Although information processing limitations encourage the evolution of brain systems that extract sameness and repeat established responses, advanced species have developed complementary neural systems for the rapid detection of deviations from sameness and for inhibiting inappropriate automatic response tendencies. The prefrontal cortex is thought to have a particularly critical, executive role in detecting deviations from familiar patterns and inhibiting automatic responses. Here we used positron−emission tomography (PET) to demonstrate that prefrontal cortex was activated when the learned and expected stimulus associations that guide behavior were violated, requiring inhibition of the prepared response and redirection of the focus of attention, in variants of a classic task of visual spatial orienting of attention.

The 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 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 taste) is reversed. This is an example of stimulus-reinforcement association learning, and is a type of stimulus-stimulus association learning. More generally, the stimulus might be a visual or olfactory stimulus, and the primary (unlearned) positive or negative reinforcer a taste or touch. A somatosensory input is revealed by neurons that respond to the texture of food in the mouth, including a population that responds to the mouth feel of fat. 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 taste and by smell. Damage to the orbitofrontal cortex can impair the learning and reversal of stimulus-reinforcement associations, and thus the correction of behaivoural responses when these are no longer appropriate because previous reinforcement contingencies change. The information which reaches the orbitofrontal cortex for these functions include information about faces, and damage to the orbitofrontal cortex can impair face (and voice) expression identification. 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 behaviour, and thus in emotion.

The model for the implementation of such working memories is an autoassociation neural network in which the memory state is kept active by continuously recirculating neuronal activity. The dorsolateral part of the prefrontal cortex receives inputs particularly from area 7 of the parietal cortex, and maybe especially involved in spatial response working memory, while the inferior convexity prefrontal cortex receives activity particularly from the inferior temporal visual cortex and maybe more involved in object working memory (Fuster, 1996; Goldman-Rakic, 1996; Rolls and Treves, 1998).