Finding the groove in neural space.

The neural signature of rhythm and tempo remains difficult to study in both humans and non-human primates. Here we recorded from the motor cortex of human participants implanted with intracortical microelectrode arrays while they performed a series of rhythmic tapping tasks. We found that rhythmic tapping elicited low-dimensional rotational neural dynamics whose radii varied in a tempo-dependent manner and axes related to kinematic properties. Moreover, we observed a spectrum of kinematic and neural behavior as participants shifted from low tempo punctuated taps to high tempo smoother, continuous taps. Surprisingly, we observed that tactile feedback strengthened the rotational dynamics despite reduced kinematic range. Moreover, while tempo preparation did not produce dynamics of their own, motor cortex encoded it in an orthogonal dimension. Finally, we found that switching tempos was achieved with smooth neural transitions that could only be separated in higher dimensions. These results show that motor cortex directly encodes a multitude of rhythm related features.