Movement quantity and frequency coding in human motor areas

Studies of movement coding have indicated a relationship between functional MRI signals and increasing frequency of movement in primary motor cortex and other motor-related structures. However, prior work has typically used block-designs and fixed-time intervals across the varying movements frequencies that may prevent ready distinction of brain mechanisms related to movement quantity and, especially, movement frequency. Here, we obtained functional MRI signals from humans working in an event-related design to extract independent activation related to movement quantity or movement frequency. Participants tapped once, twice, or thrice at 1, 2, or 3 Hz, and the tapping evoked activation related to movement quantity in the precentral and postcentral gyri, supplementary motor area, cerebellum, putamen, and thalamus. Increasing movement frequency failed to yield activation in these motor-related areas, although linear movement frequency affects occurred in nonmotor regions of cortex and subcortex. Our results do not replicate prior data suggesting movement frequency encoding in motor-related areas; instead we observed movement quantity coding in motor-related brain areas. The discrepancy between prior studies and this study likely relates to methodology concerns. We suggest that the movement quantity relationships in human motor areas and encoding of movement frequency in nonmotor areas may reflect a functional anatomical substrate for mediating distinct movement parameters.