Lidocaine inactivation of the ventral pallidum affects responding for brain stimulation reward more than it affects the stimulation's reward value

The ventral pallidum (VP) supports self-stimulation and has anatomical connections that suggest it could be linked to medial forebrain bundle (MFB) self-stimulation. Dorsal VP appears to be more related to dorsal striatopallidum and thus to cognitive control of movement, while ventral VP appears to be more related to linking motivation to action. In this study we challenged MFB self-stimulation by temporarily inactivating dorsal and ventral VP. We assessed changes in performance capacity and stimulation reward value using the rate-frequency curve shift paradigm. VP inactivation, especially in the ventral aspect of the VP ipsilateral to the stimulation site, was more likely to substantially impair maximum response rate than to affect the frequency required to maintain half-maximal responding. These effects were transient, typically disappearing within 20 min following inactivation. Contralateral inactivation was relatively ineffective and bilateral inactivation was surprisingly less effective than ipsilateral inactivation alone, although bilaterally symmetric injection sites were largely confined to the dorsal VP. The fact that inactivation-induced changes in maximum response rate were more prominent than changes in the frequency required to maintain half-maximal responding suggests a role for the ventral VP in linking reward to responding rather than detecting or computing reward value. (c) 2006 Elsevier B.V. All rights reserved.