In a series of studies, we assessed the effects of ibotenic acid lesions of the nucleus accumbens on instrumental performance in hungry rats. Although these lesions were found to generally impair lever press performance for both food pellets and a sucrose solution, they did not affect sensitivity to changes in the incentive value of the outcome induced either by a shift in food deprivation or a shift in the sucrose concentration. Further, these lesions did not affect sensitivity to a change in the instrumental contingency from response-contingent to non-contingent outcome delivery. In contrast, concurrent assessment of food magazine approach responses found that the lesion induced both a deficit in magazine entry and marked insensitivity to shifts in the incentive value of the outcome and to the changed situation that accompanied the change in instrumental contingency. These results are interpreted as suggesting (1) that nucleus accumbens lesions produce a general deficit in affective arousal; and (2) that the influence of affective mechanisms on instrumental performance may be structurally dissociated from the control of performance mediated by the action-outcome relation.