Orbitofrontal cortex

Clinic

• OFC is a prefrontal cortex region in the frontal lobes of the brain which is involved in the cognitive process of decision-making
• OFC is defined as the part of PFC that receives projections from the medial dorsal nucleus of the thalamus, and is thought to represent emotion, taste, smell and reward in decision making.

Function

• Mediating context specific responding,
• Encoding contingencies in a flexible manner,
• Encoding value esp inferred value,
• Inhibiting responses,
• Learning changes in contingency,
• Emotional appraisal,
• Altering behavior through somatic markers,
• Driving social behavior
• Representing state spaces. While most of these theories explain certain aspects of electrophysiological observations and lesion related changes in behavior, they often fail to explain, or are contradicted by other findings. One proposal that explains the variety of OFC functions is that the OFC encodes state spaces, or the discrete configuration of internal and external characteristics associated with a situation and its contingencies For example, the proposal that the OFC encodes economic value may be a reflection of the OFC encoding task state value. The representation of task states could also explain the proposal that the OFC acts as a flexible map of contingencies, as a switch in task state would enable the encoding of new contingencies in one state, with the preservation of old contingencies in a separate state, enabling switching contingencies when the old task state becomes relevant again. The representation of task states is supported by electrophysiological evidence demonstrating that the OFC responds to a diverse array of task features, and is capable of rapidly remapping during contingency shifts. The representation of task states may influence behavior through multiple potential mechanisms. For example, the OFC is necessary for ventral tegmental area (VTA) neurons to produce a dopaminergic reward prediction error, and the OFC may encode expectations for computation of RPEs in the VTA.

Specific functions have been ascribed to subregions of the OFC.

Lateral OFC has been proposed to reflect potential choice value, enabling fictive(counterfactual) prediction errors to potentially mediate switching choices during reversal, extinction and devaluation. Optogenetic activation of the lOFC enhances goal directed over habitual behavior, possibly reflecting increased sensitivity to potential choices and therefore increased switching. The mOFC, on the other hand, has been proposed to reflect relative subjective value. In rodents, a similar function has been ascribed to the mOFC, encoding action value in a graded fashion, while the lOFC has been proposed to encode specific sensory features of outcomes. The lOFC has also been proposed to encode stimulus outcome associations, which are then compared by value in the mOFC. Meta analysis of neuroimaging studies in humans reveals that a medial-lateral valence gradient exists, with the medial OFC responding most often to reward, and the lateral OFC responding most often to punishment. A posterior-anterior abstractness gradient was also found, with the posterior OFC responding to more simple reward, and the anterior OFC responding more to abstract rewards. Similar results were reported in a meta analysis of studies on primary versus secondary rewards.

The OFC and basolateral amygdala (BLA) are highly interconnected, and their connectivity is necessary for devaluation tasks. Damage to either the BLA or the OFC before, but only the OFC after devaluation impairs performance. While the BLA only responds to cues predicting salient outcomes in a graded fashion in accordance with value, the OFC responds to both value and the specific sensory attributes of cue-outcome associations. While OFC neurons that, early in learning, respond to outcome receipt normally transfer their response to the onset of cues that predict the outcome, damage to the BLA impairs this form of learning.

• Posterior orbitofrontal cortex (pOFC) is connected to the amygdala via multiple paths, that are capable of both upregulating and downregulating autonomic nervous system activity. Tentative evidence suggests that the neuromodulator dopamine plays a role in mediating the balance between the inhibitory and excitatory pathways, with a high dopamine state driving autonomic activity.

It has been suggested that the medial OFC is involved in making stimulus-reward associations and with the reinforcement of behavior, while the lateral OFC is involved in stimulus-outcome associations and the evaluation and possibly reversal of behavior. Activity in the lateral OFC is found, for example, when subjects encode new expectations about punishment and social reprisal.

The mid-anterior OFC has been found to consistently track subjective pleasure in neuroimaging studies. A hedonic hotspot has been discovered in the anterior OFC, which is capable of enhancing liking response to sucrose. The OFC is also capable of biasing the affective responses induced by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) antagonism in the nucleus accumbens towards appetitive responses.

• It is capable of modulating aggressive behavior via projections to interneurons in the amygdala that inhibit glutaminergic projections to the ventromedial hypothalamus.