Lesions of the premotor and supplementary motor areas fail to prevent implicit learning in the operant serial implicit learning task

An implicit learning deficit in people with Huntington's or Parkinson's diseases has implicated the striatum as being of importance for non-declarative learning. We have sought to identify the neurological substrate of this function using a Serial Implicit Learning Task (SILT), an operant task that requires the animal to produce 2-phase (S1 and S2) sequential nose pokes to receive a reward in the nine-hole box apparatus. Differences in performance on the speed and accuracy of responding to stimuli occurring in predictable locations over those to unpredictable locations provide an index of implicit learning, within the context of generalised performance of a skilled motor habit. Previous studies with striatal lesions demonstrated clear functional deficits on the SILT that implicated a generalised impairment in the speed and accuracy of skilled motor performance, whereas the specific implicit learning component of the task remained intact. Since imaging studies in man have identified the premotor and supplementary motor area (SMA) of the cortex as being of importance in implicit learning, we here explore the effects of similar lesions in animals on performance of the SILT. Premotor and SMA lesions produced a generalised impairment in both the accuracy and reaction time measures of SILT performance, whereas – like striatal lesions – they remained able to utilise the benefit of predictable information. A similar profile of impairments was apparent both in animals pretrained on the task prior to lesion, and in animals trained under acquisition post-lesion. The presented results suggest that the premotor and SMA are not essential for implicit learning, but are important in the performance of sequenced motor tasks.