Academic journal article International Journal of Psychology and Psychological Therapy

Orbitofrontal Cortex Inactivation Impairs Early Reversal Learning in Male Rats during a Sexually Motivated Task

Academic journal article International Journal of Psychology and Psychological Therapy

Orbitofrontal Cortex Inactivation Impairs Early Reversal Learning in Male Rats during a Sexually Motivated Task

Article excerpt

The prefrontal cortex can be defined as the cortical region where projections from the mediodorsal nucleus of the thalamus are received (Rose & Woolsey, 1948; Uylings & Van Eden, 1990). The orbitofrontal cortex (OFC) is a prefrontal subregion located in the orbital (ventral) surface of the prefrontal cortex. This area acts as a site for the convergence and integration of information received from visual, somatosensory, taste, olfactory, gustatory, and auditory cortices (Rolls & Treeves, 2001; ZaId & Kim, 1996). The OFC receives strong inputs from the amygdale (AMG) (Armony, ServanSchreiber & LeDoux, 1997; Balkenius & Moren, 2001), from the medial temporal structures such as the hippocampus, and also from the thalamic nuclei (Jowaisas, Taylor, Dewbury & Malagodi, 1971). The OFC projects back to different parts of the brain including temporal lobe areas, thalamic nuclei, hypothalamus, brain stem, basal ganglia, and other cortical regions such as the posterior parietal lobe (KoIb, 1990; Uylings & Van Eden, 1990; Uylings, Groenewegen, & KoIb, 2003). Through these widespread connections, the OFC influences a variety of autonomic, motivational, emotional and mnemonic processes in human and non-human primates (Barbas, 2000; Clark, Cools, & Robbins, 2004; Rolls, 2004; Rolls & Treeves, 2001).

The OFC plays a main role in the learning process. OFC neurons fire selectively during olfactory discrimination learning and this activity encodes specific aspects of the olfactory cues (Yonemori, Nishijo, Uwano, Tamura, Furuta, Kawasaki, Takashima, & Ono, 2000). Rats with lesions in the OFC continue to respond to stimuli, even when this behavior has not been reinforced (Clark, Cools, & Robbins, 2004; Rolls, 2000, 2004; Winstanley, Theobald, Cardinal, & Robbins, 2004), they commit more errors during discrimination tasks in the phase of extinction (Rolls, 2000, 2004) and also show a preference for immediate reinforcing experiences over longer, but delayed reinforcing experiences (Mobini, Body, Ho, Bradshaw, Szabadi, Deakin, & Anderson, 2002). It has also been observed that a lesion in the OFC alters the processes involved in reversal learning, i.e., the capacity of organisms to behave in a flexible way enabling them to identify the moment when a stimulus loses relevance and, contrastingly, where one, which was previously of no relevance, acquires it (Chudasama & Robbins, 2003; McAlonan & Brown, 2003; Schoenbaum, Setlow, Nugent, Saddoris, & Gallagher, 2003a; Schoenbaum, Setlow, & Ramus, 2003b).

Schoenbaum, Chiba, & Gallagher (2000), have reported that firing rate of OFC neurons is incremented on late phases and even more enhanced once the rat have achieved the number of correct responses criterion in discrimination learning. They found also an increase in correlated activity of OFC neurons in reversal phase. On these basis authors propose that OFC activity is specifically related to the improving accuracy in task performance. In contrast, Rolls and Treeves (2001), have propose that OFC could be involved since early phases of learning, by contributing to the acquisition of reward value of stimulus through its connections with amygdala. These different approaches could be framed in Balleine and Dickinson (1998) hypothesis about two different mechanisms of instrumental motivated behavior, both implying prefrontal cortex. One mechanism, called stimulus-response habits, is more related with over-training based on instrumental contingency between response and reward and could be mediated by prefrontal-striatum circuits (Borchgrave, Rawlins, Dickinson, & Balleine, 2002). The other mechanism, named goal-directed process, implicate the acquisition of incentive value and could be mediated by limbic-prefrontal circuits, including amygdala (Hall, Parkinson, Connor, Dickinson, & Everitt, 2001).

Various experimental designs have been developed in order to demonstrate the role played by OFC in this type of learning processes, using incentives such as food or drink as primary reinforcing experiences (Chudasama & Robbins, 2003; Rolls, 2000; Schoenbaum, Chiba, & Gallagher, 2000; Schoenbaum, Setlow, Nugent, Saddoris, & Gallagher, 2003a; Schoenbaum, Setlow, & Ramus, 2003b). …

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