Cortical activations associated with auditorily paced finger tapping.

We investigated neuromagnetic responses during an auditorily paced synchronization task using a 122-channel whole-head neuromagnetometer. Eight healthy right handed subjects were asked to synchronize left and right unilateral finger taps to a regular binaural pacing signal. Synchronization of the right hand with an auditory pacing signal is known to be associated with three tap-related neuromagnetic sources localized in the contralateral primary sensorimotor cortex. While the first source represents the neuromagnetic correlate of the motor command the second one reflects somatosensory feedback due to the finger movement. The functional meaning of the third source, which is also localized in the primary somatosensory cortex is still unclear. On the one hand this source represents a neuromagnetic correlate of somatosensory feedback due to the finger tap. On the other hand it has been suggested that the function of this source could additionally represent a cognitive process, which enables the subject to monitor the time distance between taps and clicks. The aim of the present study was to elucidate the function of this source, which would fundamentally reform the meaning of the primary somatosensory cortex in the timing of movements with respect to external events. The data of the present study demonstrate that the three sources in the contralateral sensorimotor cortex are stronger related to the tap than to the click. This result contradicts the assumption of a cognitive process localized in the primary somatosensory cortex. Thus, activation in the primary somatosensory cortex most likely represents exclusively somatosensory feedback and no further cognitive processes.