The foundation of modern neuroscience and psychology about intention for action was laid by Libet and his colleagues (Libet, B., et al, Brain 106: 623-42, 1983). They reported the time of awareness of wanting to move to be about 0.2 s before voluntary movement onset. However, despite repeated confirmation of the result, their method has been criticized for its dependence on self-reported timing and subjective memory and the interpretation has been widely debated without general consensus. Here, we show that the mean time of the conscious intention to move was 1.42 seconds before movement, estimated based on subjects’ real-time decision of whether or not there was a thought to move when a tone occurred. This event is after the onset of the Bereitschaftspotential, an electroencephalographic activity preceding voluntary movement, but about one second earlier than the timing of intention reported previously based on subject’s recall. Our result solves some problems of the conventional method, thus giving clearer answer to the controversies. The difference between the conventional result and our result suggests that the perception of intention rises through multiple levels of awareness, starting just after the brain initiates movement.

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In human, both primary and nonprimary motor areas are involved in the control of voluntary movements. However, the dynamics of functional coupling among different motor areas has not been fully clarified yet. Because it has been proposed that the functional coupling among cortical areas might be achieved by the synchronization of oscillatory activity, we investigated the electrocorticographic coherence between the supplementary motor and primary sensorimotor areas (SMA and S1-M1) by means of event-related partial coherence analysis in 11 intractable epilepsy patients. We found premovement increase of coherence between the SMA proper and S1-M1 at the frequency of 0-33 Hz and between the pre-SMA and S1-M1 at 0-18 Hz. Coherence between the SMA proper and M1 started to increase 0.9 sec before the movement onset and peaked 0.3 sec after the movement. There was no systematic difference within the SMA (SMA proper vs pre-SMA) or within the S1-M1, in terms of the time course as well as the peak value of coherence. The phase spectra revealed near-zero phase difference in 57% (20 of 35) of region pairs analyzed, and the remaining pairs showed inconsistent results. This increase of synchronization between multiple motor areas in the preparation and execution of voluntary movements may reflect the multiregional functional interactions in human motor behavior.

The early occurrence of ictal DC shifts warrants further studies to determine the role of glia (possibly mediating ictal DC shifts) in seizure generation.

Somesthetic temporal discrimination (STD) is impaired in focal hand dystonia (FHD). We explored the electrophysiological correlate of the STD deficit to assess whether this is due to dysfunction of temporal inhibition in the somatosensory inhibitory pathway or due to dysfunction in structures responsible for nonmodality-specific timing integration. Eleven FHD patients and 11 healthy volunteers were studied. STD threshold was investigated as the time interval required for perceiving a pair of stimuli as two separate stimuli in time. We also examined the somatosensory-evoked potential (SEP) in a paired-pulse paradigm. We compared STD threshold and recovery function of SEP between the groups. STD thresholds were significantly greater in FHD than in healthy volunteers. The amount of P27 suppression in the 5 ms-ISI condition was significantly less in FHD. It was also found that the STD threshold and P27 suppression were significantly correlated: the greater the STD threshold, the less the P27 suppression. Significantly less suppression of P27 with a lack of significant change in N20 indicates that the impairment of somatosensory information processing in the time domain is due to dysfunction within the primary somatosensory cortex, suggesting that that the STD deficit in FHD is more attributable to dysfunction in the somatosensory pathway.