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4 Orbitofrontal Cortex (OFC)

The OFC associates sensory stimuli with reward related information (Schoenbaum et al., 2009) or in other words it computes the (potential) reward value of a sensor cue (Bari and Robbins, 2013; Wikenheiser and Schoenbaum, 2016).

4.1 Afferents

The OFC receives inputs from a wide range of brain areas which allows it associate sensor cues (and also actions) to rewards. Wikenheiser and Schoenbaum (2016) provides an overview of these inputs which are from the:

hippocampus
subiculum
PFC
perihirnal cortex, and
nucleus reuniens

Serotonin seems to have a strong effect on the OFC which has been shown by Zhou et al. (2015). Stimulation of the DRN results in both excitatory activity and inhibitory activity in the OFC. In addition the release of 5HT has a strong impact on plasticity: after pairing an odour stimulus with the release of 5HT the odour stimulus creates long lasting activity in the OFC which starts at the presentation of the stimulus and ends after reward delivery (Zhou et al., 2015).

4.2 Efferents

Its major subcortical targets include the dorsal Raphe nucleus (DRN) (Luo et al., 2015), medial striatum, NAcc, lateral pre-optic area, amygdala and the hypothalamus (Vertes et al., 2012).

The l-OFC innervates the l-shell and amygdala and
the m-OFC the m-shell, hippocampus and amygdala (Noonan et al., 2012; Brog et al., 1993b)

4.3 Neuronal activity

The paper by (Tremblay and Schultz, 1999) proposed that OFC neurons code the motivational value of rewards. The activity of OFC neurons increased in response to reward-predicting stimuli, during the expectation of rewards, and after the receipt of rewards. Also actions, associated with rewards, increase the firing rates of OFC neurons (Wikenheiser and Schoenbaum, 2016).

4.4 Behavioural experiments

The review by (Wikenheiser and Schoenbaum, 2016) presents behavioural experiments involving the OFC which confirm that the OFC computes behavioural reward value computed from sensory cues, such as odour, and actions. They contrast this to the hippocampus which computes reward value in relation to place fields.

Spatial reversal learning is improved by injecting the 5-HT(2C) receptor antagonist into the OFC (Boulougouris and Robbins, 2010).

Reversal learning is impaired if 5HT processing is disrupted in the OFC (Bari and Robbins, 2013).