The ventral striato-pallidal pathway mediates the effect of predictive learning on choice between goal-directed actions

Abstract

The nucleus accumbens shell(NAc-S)playsanimportant roleintheway stimuli that predict reward affectthe performance of, and choice between, goal-directed actions in tests of outcome-specific Pavlovian-instrumental transfer (PIT). The neural processes involved in PIT downstream of the ventral striatum are, however, unknown. The NAc-S projects prominently to the ventral pallidum (VP), and in the current experiments, we assessed the involvement of the NAc-S to VP projection in specific PIT in rats. We first compared expression of the immediate-early gene c-Fos in the medial (VP-m) and lateral (VP-l) regions of the VP and in addition, used the retrograde tracer Fluoro-gold combined with c-Fos to assess the involvement ofthese pathways during PIT. Although there wasnoevidenceof differential activation in neurons in the VP-l, the VP-m showed a selective increase in activity in rats tested for PIT compared with appropriate controls, as did NAc-S neurons projecting to the VP-m. To confirm that VP-m activity is important for PIT, we inactivated this region before test and found this inactivation blocked the influence of predictive learning on choice. Finally, to confirm the functional importance of the NAc-S to VP-m pathway we used a disconnection procedure, using asymmetrical inactivation of the NAc-S and either the ipsilateral or contralateralVP-m. Specific PIT was blocked but onlyby inactivationof the NAc-S and VP-m in contralateral hemispheres. These results suggest that the NAc-S and VP-m form part of a circuit mediating the effects of predictive learning on choice. © 2013 the authors.