The neural basis of audiomotor entrainment: an ALE meta-analysis

Sensorimotor synchronization (SMS) is the coordination of rhythmic movement with an external rhythm, ranging from finger tapping in time with a metronome to musical ensemble performance. An earlier review (Repp, 2005) covered tapping studies; two additional reviews (Repp, 2006a, b) focused on music performance and on rate limits of SMS, respectively. The present article supplements and extends these earlier reviews by surveying more recent research in what appears to be a burgeoning field. The article comprises four parts, dealing with (1) conventional tapping studies, (2) other forms of moving in synchrony with external rhythms (including dance and nonhuman animals' synchronization abilities), (3) interpersonal synchronization (including musical ensemble performance), and (4) the neuroscience of SMS. It is evident that much new knowledge about SMS has been acquired in the last 7 years.

Although there has been an explosion of interest in the neural correlates of time perception during the past decade, substantial disagreement persists regarding the structures that are relevant to interval timing. We addressed this important issue by conducting a comprehensive, voxel-wise meta-analysis using the activation likelihood estimation algorithm; this procedure models each stereotactic coordinate as a 3D Gaussian distribution, then tests the likelihood of activation across all voxels in the brain (Turkeltaub et al., 2002). We included 446 sets of activation foci across 41 studies of timing that report whole-brain analyses. We divided the data set along two dimensions: stimulus duration (sub- vs. supra-second) and nature of response (motor vs. perceptual). Our meta-analyses revealed dissociable neural networks for the processing of duration with motor or perceptual components. Sub-second timing tasks showed a higher propensity to recruit sub-cortical networks, such as the basal ganglia and cerebellum, whereas supra-second timing tasks were more likely to activate cortical structures, such as the SMA and prefrontal cortex. We also detected a differential pattern of activation likelihood in basal ganglia structures, depending on the interval and task design. Finally, a conjunction analysis revealed the SMA and right inferior frontal gyrus as the only structures with significant voxels across all timing conditions. These results suggest that the processing of temporal information is mediated by a distributed network that can be differentially engaged depending on the task requirements.

This review summarizes recent investigations of temporal processing. We focus on motor and perceptual tasks in which crucial events span hundreds of milliseconds. One key question concerns whether the representation of temporal information is dependent on a specialized system, distributed across a network of neural regions, or computed in a local task-dependent manner. Consistent with the specialized system framework, the cerebellum is associated with various tasks that require precise timing. Computational models of timing mechanisms within the cerebellar cortex are beginning to motivate physiological studies. Emphasis has also been placed on the basal ganglia as a specialized timing system, particularly for longer intervals. We outline an alternative hypothesis in which this structure is associated with decision processes.