Amphetamine disrupts negative patterning but does not produce configural association deficits on an alternative task

Three experiments investigated the effects of d-amphetamine on the performance of rats on tasks that required the discrimination of configural cues (i.e., those in which two stimulus elements, tone and light, have a meaning when presented together that is distinct from the meaning of the same elements presented in isolation from each other). In a negative patterning task (Experiment 1), rats were trained in a GO/NO-GO task in which either stimulus alone signalled reward availability whilst the compound did not. Amphetamine (0.5, 1.0 and 2.0 mg/kg) was found to disrupt performance by increasing responses to the unrewarded compound. Responses were also increased during the ITI. In contrast, in Experiments 2 and 3 amphetamine had little impact on performance on a task in which the rats had to respond to either of the single stimuli with one response (lever-press or chain-pull) and to the compound stimulus with the other response. The results add credence to the suggestion of Davidson et al. (Behav. Neurosci., 1993, 107, 227-234) that hippocampal lesions disrupt negative patterning by increasing responsiveness rather than by disrupting a configural association system and do not support the idea that increased dopamine activity disrupts configural associations. The findings are discussed in the context of hippocampal-dopamine interactions.