Cholinergic modulation of motor sequence learning
The cholinergic system plays a key role in motor function, but whether pharmacological modulation of cholinergic activity affects motor sequence learning is unknown. The acetylcholine receptor antagonist biperiden, an established treatment in movement disorders, reduces attentional modulation, but whether it influences motor sequence learning is not clear. Using a randomized, double-blind placebo-controlled crossover design, we tested thirty healthy young participants and show that biperiden impairs production of sequential finger movements following a fixed but not a random sequence. A similar interaction was observed in widespread oscillatory broadband power changes (4-25 Hz) in the motor sequence learning network after receiving biperiden, with greater power in the theta, alpha, and beta bands over ipsilateral motor and bilateral parietal-occipital areas. The reduced theta power during a fixed compared to random sequence, likely reflecting disengagement of top-down attention to sensory processes, was disrupted by biperiden. The alpha synchronization during learned sequences, reflecting sensory gating and lower visuospatial attention requirements for the learned, compared with visuomotor responses to a random sequence, was greater after biperiden, potentially reflecting excessive visuospatial attention reduction following biperiden, also affecting visuomotor responding required to enable sequence learning. Beta oscillations facilitate sequence learning by integrating visual and somatosensory inputs, stabilizing learned sequences, and promoting prediction of the next stimulus. The beta synchronization after biperiden fits with a disruption of the selective visuospatial attention enhancement associated with initial sequence learning. These findings highlight the role of cholinergic processes in motor sequence learning.