Endogenous neuromagnetic activity for mental hierarchy of timing.

The frontal-striatal circuits, the cerebellum, and motor cortices play crucial roles in processing timing information on second to millisecond scales. However, little is known about the physiological mechanism underlying human's preference to robustly encode a sequence of time intervals into a mental hierarchy of temporal units called meter. This is especially salient in music: temporal patterns are typically interpreted as integer multiples of a basic unit (i.e., the beat) and accommodated into a global context such as march or waltz. With magnetoencephalography and spatial-filtering source analysis, we demonstrated that the time courses of neural activities index a subjectively induced meter context. Auditory evoked responses from hippocampus, basal ganglia, and auditory and association cortices showed a significant contrast between march and waltz metric conditions during listening to identical click stimuli. Specifically, the right hippocampus was activated differentially at 80 ms to the march downbeat (the count one) and approximately 250 ms to the waltz downbeat. In contrast, basal ganglia showed a larger 80 ms peak for march downbeat than waltz. The metric contrast was also expressed in long-latency responses in the right temporal lobe. These findings suggest that anticipatory processes in the hippocampal memory system and temporal computation mechanism in the basal ganglia circuits facilitate endogenous activities in auditory and association cortices through feedback loops. The close interaction of auditory, motor, and limbic systems suggests a distributed network for metric organization in temporal processing and its relevance for musical behavior.