Functional MRI reveals the existence of modality and coordination-dependent timing networks.

Growing evidence suggests that interval timing in humans is supported by distributed brain networks. Recently, we demonstrated that the specific network recruited for the performance of rhythmic timing is not static but is influenced by the coordination pattern employed during interval acquisition. Here we expand on this previous work to investigate the role of stimulus modality and coordination pattern in determining the brain areas recruited for performance of a self-paced rhythmic timing task. Subjects were paced with either a visual or an auditory metronome in either a synchronized (on the beat) or syncopated (off the beat) coordination pattern. The pacing stimulus was then removed and subjects continued to move based on the required interval. When compared with networks recruited for auditory pacing and continuation, the visual-specific activity was observed in the classic dorsal visual stream that included bilateral MT/V5, bilateral superior parietal lobe, and right ventral premotor cortex. Activity in these regions was present not only during pacing, when visual information is used to guide motor behavior, but also during continuation, when visual information specifying the temporal interval was no longer present. These results suggest a role for modality-specific areas in processing and representing temporal information. The cognitive demands imposed by syncopated coordination resulted in increased activity in a broad network that included supplementary motor area, lateral pre-motor cortex, bilateral insula, and cerebellum. This coordination-dependent activity persisted during the subsequent continuation period, when stimuli were removed and no coordination constraints were imposed. Taken together, the present results provide additional evidence that time and timing are served by a context-dependent distributed network rooted in basic sensorimotor processes.

Neural substrates of real and imagined sensorimotor coordination.

Much debate in the behavioral literature focuses on the relative contribution of motor and perceptual processes in mediating coordinative stability. To a large degree, such debate has proceeded independently of what is going on in the brain. Here, using blood oxygen level-dependent measures of neural activation, we compare physically executed and imagined rhythmic coordination in order to better assess the relative contribution of hypothesized neuromusculoskeletal mechanisms in modulating behavioral stability. The executed tasks were to coordinate index finger to thumb opposition movements of the right hand with an auditory metronome in either a synchronized (on the beat) or syncopated (off the beat) pattern. Imagination involved the same tasks, except without physical movement. Thus, the sensory stimulus and coordination constraints were the same in both physical and imagination tasks, but the motoric requirements were not. Results showed that neural differences between executed synchronization and syncopation found in premotor cortex, supplementary motor area, basal ganglia and lateral cerebellum persist even when the coordinative patterns were only imagined. Neural indices reflecting behavioral stability were not abolished by the absence of overt movement suggesting that coordination phenomena are not exclusively rooted in purely motoric constraints. On the other hand, activity in the superior temporal gyrus was modulated by both the presence of movement and the nature of the coordination, attesting to the intimacy between perceptual and motoric processes in coordination dynamics.

Spatiotemporal analysis of the neuromagnetic response to rhythmic auditory stimulation: rate dependence and transient to steady-state transition.

OBJECTIVE: Whole head magnetoencephalography was used to investigate the spatiotemporal dynamics of neuromagnetic brain activity associated with rhythmic auditory stimulation. METHODS: In order to characterize the evolution of the auditory responses we applied a Karhunen-Loève decomposition and k-means cluster analysis to globally compare spatial patterns of brain activity at different latencies and stimulation rates. Tones were presented binaurally at 27 different stimulation rates within a perceptually and behaviorally relevant range from 0.6 to 8.1 Hz. RESULTS: Over this range, we observed a linear increase of the amplitude of the main auditory response at 100 ms latency (N1m) with increasing inter-stimulus interval, and qualitative changes of the overall spatiotemporal dynamics of the auditory response. In particular, a transition occurred between a transient evoked response at low frequencies, and a continuous steady-state response at high frequencies. CONCLUSIONS: We show the onset of temporal overlap between responses to successive tones that leads to this transition. Response overlap begins to occur near 2 Hz, marking the onset of a continuous perceptual representation.

Neuromagnetic activity in alpha and beta bands reflect learning-induced increases in coordinative stability.

OBJECTIVE: To investigate how learning induced increases in stability on a syncopation task are manifest in the dynamics of cortical activity. METHOD: Magnetoencephalography was recorded from 143 sensors (CTF Systems, Inc). A pre-training procedure determined the critical frequency (F(c)) for each subject (n=4). Subjects either syncopated or synchronized to a metronome that increased in frequency from 1.2 to 3.0 Hz in 0.2 Hz steps. The F(c) was the point at which subjects spontaneously switched from syncopation to synchronization. Subjects then underwent 100 training trials (with feedback) at F(c). Following the learning phase the pre-training procedure was repeated. RESULTS: An increase in the F(c) occurred indicating that practice improved the stability of syncopation. The transition delay was also observed in the phase of the time-averaged signal in sensors over the contralateral sensorimotor area and in power analysis in the 8-12 Hz and 18-24 Hz frequency bands. Initially, reduced power was observed bilaterally during syncopation compared to synchronization. Following training, these differences were reduced or eliminated. CONCLUSION: Pre-training power differences can be explained by the greater difficulty of the syncopation task. The reduction in power differences following training suggests that at the cortical level, syncopation became more similar to synchronization possibly reflecting a decrease in task and/or attention demands.