Unified control of temporal and spatial scales of sensorimotor behavior through neuromodulation of short-term synaptic plasticity

Abstract

Neuromodulators such as dopamine have been shown to modulate short-term synaptic plasticity (STP). Here we propose that the neuromodulation of STP provides a general mechanism to scale neural dynamics and motor outputs in time and space. We trained RNNs that incorporated STP to produce complex motor trajectories-handwritten digits-with different temporal (speed) and spatial (size) scales. The learned dynamics underwent temporal and spatial scaling when higher synaptic release probabilities corresponded to higher speed/size. Neuromodulation of STP enhanced temporal or spatial generalization compared to weight modulation alone. The model accounted for the data of two experimental studies involving flexible sensorimotor timing. Our results address a long-standing debate regarding the role of dopamine in timing and predict novel mechanisms by which dopamine may slow down neural dynamics and thus slow 'clock' speed.

A window on Subjective Time

“…Similarly, exactly how estimates of rate of change modulate neural dynamics is an open question. A simple multiplicative factor on the recurrent and input matrices is feasible (as demonstrated in Chapter 2), but neurophysiological mechanisms that more directly modulate the dynamics, such as short-term synaptic plasticity (Zhou & Buonomano, 2022), deserve further attention. At the very least, this simple formalization of 'adaptive dynamics' should motivate theorists and experimentalists to take a critical look at the temporal properties of their equations and experiments.…”