The medial prefrontal cortex is crucial for the maintenance of persistent licking and the expression of incentive contrast.

Marc A Parent,Mark Laubach,Linda M Amarante,Benjamine Liu,Damian Weikum

doi:10.3389/fnint.2015.00023

Abstract

We examined the role of the medial prefrontal cortex (mPFC) in reward processing and the control of consummatory behavior. Rats were trained in an operant licking procedure in which they received alternating access to solutions with relatively high and low levels of sucrose (20 and 4%, w/v). Each level of sucrose was available for fixed intervals of 30 s over 30 min test sessions. Over several days of training, rats came to lick persistently when the high level of sucrose was available and suppressed licking when the low level of sucrose was available. Pharmacological inactivations of the mPFC, specifically the rostral part of the prelimbic area, greatly reduced intake of the higher value fluid and only slightly increased intake of the lower value fluid. In addition, the inactivations altered within-session patterns and microstructural measures of licking. Rats licked equally for the high and low levels of sucrose at the beginning of the test sessions and “relearned” to reduce intake of the low value fluid over the test sessions. Durations of licking bouts (clusters of licks with inter-lick intervals <0.5 s) were reduced for the high value fluid and there were many more brief licking bouts (<1 s) when the low value fluid was available. These effects were verified using an alternative approach (optogenetic silencing using archaerhodopsin) and were distinct from inactivation of the ventral striatum, which simply increased overall intake. Our findings suggest that the mPFC is crucial for the maintenance of persistent licking and the expression of learned feeding strategies.

Highlights

The prefrontal cortex is crucial for using learned rules to control behavior (Miller and Cohen, 2001)
Inactivation of the medial prefrontal cortex (mPFC) alters the pace at which a given behavioral task is performed (Horst and Laubach, 2009). These effects may be due to the role of the mPFC in behavioral inhibition, as a number of studies have found that the mPFC is involved in controlling actions that must be postponed over extended periods of time, i.e., the ability to wait before acting (Muir et al, 1996; Passetti et al, 2002; Chudasama et al, 2003; Risterucci et al, 2003; Narayanan et al, 2006; Bari and Robbins, 2013)
The rats licked more slowly and with more variability with the rostral mPFC inactivated. (A ninth rats included in the analysis reported in the section above and Figure 4 was excluded from this analysis due to having much higher levels of variation No consistent effect was found on another measure of variability, the coefficient of variation [t(8) = 2.03, p = 0.08; Figure 5C), defined as variance divided by mean

Summary

Introduction

The prefrontal cortex is crucial for using learned rules to control behavior (Miller and Cohen, 2001). Lesion studies in rodents have established that rule-guided behavior depends on the prelimbic cortex (aka area 32), which is part of the medial prefrontal cortex (mPFC; Delatour and GisquetVerrier, 1996, 1999) This cortical region is found in all mammals (Laubach, 2011) and is thought to have homologies across species both anatomically (Vogt et al, 2013; Vogt and Paxinos, 2014) and functionally (Narayanan et al, 2013). An encoding of behavioral outcome may arise through modulations of mPFC neurons that are phase locked to the onset of reward consumption (Horst and Laubach, 2012, 2013)

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Conclusion