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Abstract From electroencephalographic recordings, we estimated the surface Laplacian over motor areas in a Stroop-like between-hand choice reaction time task in humans. Response-locked averages showed a (negative) “motor potential” over the primary motor areas contralateral to the response. At the same time, a positive wave was observed over the primary motor areas ipsilateral to the response. These data suggest that, when a between-hand choice is required, an inhibition of the primary motor cortex ipsilateral to the nonresponding hand is implemented. This observation is relevant to the interpretation of the lateralized readiness potential (LRP) because the LRP is blind to the respective contribution of the contralateral and ipsilateral motor cortices. In addition, a negative wave beginning about 200 ms before EMG onset and peaking about 50 ms before it occurred over the supplementary motor areas (FCz). This wave preceded the motor potential, which supports the view that the supplementary motor areas are upstream in a hierarchy of the motor command. [ABSTRACT FROM AUTHOR]

Typing is a pervasive phenomenon, yet the underlying neural processes have hardly been studied. Here, the mechanisms of keystroke preparation were studied with a typed picture-naming task performed by expert typists. Electroencephalographic activities recorded over sensorimotor areas prior to first-keystroke onset were examined with time-frequency and event-related potential ( ERP) analyses. In the time-frequency domain, a beta event-related desynchronization was present bilaterally. In the ERP analyses, the activity was asymmetric, with negativity and positivity patterns developing over, respectively, contra- and ipsilateral recording sites. This pattern is similar to that observed in choice reaction time tasks, and thus can be interpreted as evidence of contralateral motor cortex activation accompanied by inhibition of the ipsilateral motor cortex. These data constitute the first electrophysiological demonstration of inhibitory activity in typing and pave the way to a thorough study of typing. [ABSTRACT FROM AUTHOR]