Neuronal oscillations are a ubiquitous phenomenon in the human nervous system. Alpha-band oscillations (8–12 Hz) have been shown to correlate negatively with attention and performance, whereas gamma-band oscillations (40–150 Hz) correlate positively. Here, we studied the relation between prestimulus alpha-band power and poststimulus gamma-band power in a suprathreshold tactile discrimination task. Participants received two electrical stimuli to their left index finger with different SOAs (0 msec, 100 msec, intermediate SOA, intermediate SOA ± 10 msec). The intermediate SOA was individually determined so that stimulation was bistable, and participants perceived one stimulus in half of the trials and two stimuli in the other half. We measured neuronal activity with magnetoencephalography (MEG). In trials with intermediate SOAs, behavioral performance correlated inversely with prestimulus alpha-band power but did not correlate with poststimulus gamma-band power. Poststimulus gamma-band power was high in trials with low and high prestimulus alpha-band power and low for intermediate prestimulus alpha-band power (i.e., U-shaped). We suggest that prestimulus alpha activity modulates poststimulus gamma activity and subsequent perception: (1) low prestimulus alpha-band power leads to high poststimulus gamma-band power, biasing perception such that two stimuli were perceived; (2) intermediate prestimulus alpha-band power leads to low gamma-band power (interpreted as inefficient stimulus processing), consequently, perception was not biased in either direction; and (3) high prestimulus alpha-band power leads to high poststimulus gamma-band power, biasing perception such that only one stimulus was perceived.

The posterior parietal cortex and the cerebellum are assumed to contribute to anticipatory motor control. Thus, it is reasonable that these areas act as a functional unit. To identify a neural signature of anticipatory motor control, 11 healthy volunteers performed a bimanual finger-tapping task with respect to isochronous (i.e., regular) and randomized (i.e., irregular) auditory pacing. Neuromagnetic activity was recorded using a 122-channel whole-head neuromagnetometer. Functional interaction between spatially distributed brain areas was determined by measures of tap-related phase synchronization. Assuming that (i) the cerebellum predicts sensory events by an internal model and (ii) the PPC maintains this prediction, we hypothesized that functional interaction between both structures varies depending on the predictability of the pacing signal. During isochronous pacing, functional connectivity within a cerebello-diencephalic-parietal network before tap onset was evident, suggesting anticipatory motor control. During randomized pacing, however, functional connectivity after tap onset was increased within a parietal-cerebellar loop, suggesting mismatch detection and update of the internal model. Data of the present study imply that anticipatory motor control is implemented in a network-like manner. Our data agree well with the hypothesis that functional connectivity in a cerebello-diencephalic-parietal loop might be crucial for anticipatory motor control, whereas parietal-cerebellar interaction might be critical for feedback processing.

Compared to unimanual task execution, simultaneous bimanual tapping tasks are associated with a significantly reduced intertap variability. It has been suggested that this bimanual advantage is based on the integration of timing signals which otherwise control each hand independently. Although its functional and anatomic foundations are poorly understood, functional coupling between cerebellar hemispheres might be behind this process. Because the execution of fast alternating fingertaps increases intertap variability, it is hypothesized that intercerebellar coupling is reduced in such tasks. To shed light on the functional significance of intercerebellar coupling, 14 right-handed subjects performed unimanual right, bimanual simultaneous, and bimanual alternating synchronization tasks with respect to a regular auditory pacing signal. In all conditions, within-hand intertap interval was 500 msec. Continuous neuromagnetic activity, using a 122-channel wholehead neuromagnetometer and surface electromyograms of the first dorsal interosseus muscle of both hands, were recorded. For data analysis, we used the analysis tool Dynamic Imaging of Coherent Sources , which provides a tomographic map of cerebromuscular and cerebrocerebral coherence. Analysis revealed a bilateral cerebello-thalamo-cortical network oscillating at alpha (8–12 Hz) and beta (13–24 Hz) frequencies associated with bimanual synchronization. In line with our hypothesis, coupling between cerebellar hemispheres was restricted to simultaneous task execution. This result implies that intercerebellar coupling is key for the execution of simultaneous bimanual movements. Although the criticality of a specific magneto-encephalography pattern for behavioral changes should be interpreted with caution, data suggest that intercerebellar coupling possibly represents the functional foundation of the bimanual advantage.

Sensorimotor synchronization tasks, in which subjects have to tap their finger in synchrony with an isochronous auditory click, typically reveal a synchronization error with the tap preceding the click by about 20 to 50 msec. Although extensive behavioral studies and a number of different explanatory accounts have located the cause of this so-called “negative asynchrony” on different levels of processing, the underlying mechanisms are still not completely understood. Almost nothing is known about the central processes, in particular, which sensory or motor events are synchronized by subjects. The present study examined central-level processing in synchronization tasks with magnetoencephalography (MEG). Eight subjects synchronized taps with their right index finger to an isochronous binaural pacing signal presented at an interstimulus interval of 800 msec. To gain information on central temporal coupling between “tap” and “click”, evoked responses were averaged time-locked to the auditory signal and the tap onset. Tap-related responses could be explained with a three dipole model: One source, peaking at approximately 77 msec before tap onset, was localized in contralateral primary motor cortex (MI); the two other sources, peaking approximately at tap onset and 75 msec after tap onset, in contralateral primary somatosensory cortex (SI). Temporal coupling of these sources was compared in relation to different trigger points. The second SI source was equally well time-locked to the tap and to the auditory click. Furthermore, analysis of the time locking of this source activity as a function of the temporal order of tap and click showed that the second event—irrespective whether tap or click—was decisive in triggering the second SI source. This suggests that subjects use mainly sensory feedback in judging and evaluating whether they are “keeping time.”