Cortical plasticity of spatial stimulus-response associations: electrophysiological and behavioral evidence

Right-handed subjects tend to respond faster to stimuli presented in the vi sual hemifield that spatially corresponds to the responding hand. In a typi cal Simon task, response is based on a non-spatial salient feature of the s timulus (e.g. color) whereas its position must be ignored. However, the spa tial position of the stimulus interferes with the processing of the salient characteristic. Subjects are significantly faster when stimulus side and r esponse side correspond (corresponding condition) than when they do not (no n-corresponding condition). We have previously shown with behavioral experi ments that, when subjects practice reversed contingencies (that is, spatial ly incompatible trials) in a session preceding the Simon task, they show a long-term retention of these associations, resulting in the disappearance o f the latency cost typically observed in non-corresponding trials. Here we show, by means of the lateralized readiness potential, that the neural corr elate of such behavioral plasticity is an increase in premotor cortex activ ation during preparation of non-corresponding responses. This effect showed a marked left-right asymmetry which suggests an important role of subjects ' handedness. Our results demonstrate that humans can learn in a single ses sion to reverse relatively stable stimulus-response associations. NeuroRepo rt 12:973-977 (C) 2001 Lippincott Williams & Wilkins.