Electrical Stimulation of the Medial Prefrontal Cortex Supports Both \u27Pure Reward\u27 and \u27Reward-Escape\u27 Behavior in Rats

In female Sprague-Dawley rats, 8 of 12 medial prefrontal cortex (MPFC) sites that yielded criterion self-stimulation behavior supported only self-stimulation, i.e. were ‘pure reward’ in type. The remaining 4 sites supported behavior to escape from experimenter-administered stimulation of the same parameter as well, i.e. were ‘reward-escape’ in type. ‘Pure reward’ and ‘reward-escape’ sites in the MPFC were distinguished by both the magnitude and temporal form of the escape response functions generated, and by the prevalence of ‘pounce-back’, a vigorous and repetitive barpressing during the 3-s MPFC stimulation-escape interval produced by an effective barpress. The finding that both ‘pure reward’ and ‘reward-escape’ patterns of behavior can be elicited by stimulation on the MPFC provides a basis for futher assessment of similarities and differences in medial prefrontalcortical and lateral hypothalamic (LH) ‘reward’ systems. It is suggested that ‘reward-escape’ in the MPFC may be mediated by the activity of ‘reward’ neurones which respond to stimulus offset, rather than by a secondary aversive process as is proposed to underlie ‘reward-escape’ in the LH

Hedonic Interactions of Medial Prefrontal Cortex and Nucleus Reticularis Gigantocellularis

It has been shown that ‘pure reward’ and ‘reward-escape’ sites in the lateral hypothalamus (LH) of rats respectively ameliorate and exacerbate nucleus reticularis gigantocellularis (NGC) stimulation-induced aversion52. Conversely, the present studies found that ‘rewarding’ medial prefrontal cortex (MPFC) stimulation increased escape from NGC stimulation regardless of whether the MPFC site tested was ‘pure reward’ or ‘reward-escape’ in type. This suggested that a simple algebraic summation model of positive and negative affective processes may not adequately describe the NGC-MPFC interaction. In a subsequent study, rats were observed both to barpress less to obtain, and more to escape from, ‘rewarding’ MPFC stimulation during continuous NGC stimulation, supporting the hypothesis that the observed MPFC stimulation-mediated increase in NGC stimulation escape reflected an exacerbation of aversion. Finally, NGC stimulation was seen to increase barpressing to obtain ‘subreward’ MPFC current trains, indicating a potentiation of the reward value of such current. Results of this series of studies suggests a hedonic interaction model of NGC and MPFC characterized by reciprocal neuromodulation. The model is conceptuallized as a ‘neural opponent process’ subserving affective ‘balance’ and ‘feature enhancement’, and its possible relevance to the putative role of the MPFC in cocaine use is discussed