Electrical stimulation of the medial prefrontal cortex supports both 'pure reward' and 'reward-escape' 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.