EFFECTS OF IBOTENIC ACID LESIONS OF THE NUCLEUS-ACCUMBENS ON INSTRUMENTAL ACTION

In a series of studies, we assessed the effects of ibotenic acid lesio ns of the nucleus accumbens on instrumental performance in hungry rats . Although these lesions were found to generally impair lever press pe rformance for both food pellets and a sucrose solution, they did not a ffect sensitivity to changes in the incentive value of the outcome ind uced either by a shift in food deprivation or a shift in the sucrose c oncentration. Further, these lesions did not affect sensitivity to a c hange in the instrumental contingency from response-contingent to non- contingent outcome delivery. In contrast, concurrent assessment of foo d magazine approach responses found that the lesion induced both a def icit in magazine entry and marked insensitivity to shifts in the incen tive Value of the outcome and to the changed situation that accompanie d the change in instrumental contingency. These results are interprete d as suggesting (1) that nucleus accumbens lesions produce a general d eficit in affective arousal; and (2) that the influence of affective m echanisms on instrumental performance may be structurally dissociated from the control of performance mediated by the action-outcome relatio n.