Effects of clinically-relevant electrical stimulation of macaque sensorimotor cortex on neural activity and behavior

Abstract

Electrical stimulation is a popular technique for neuromodulation in research, but the scope of approved therapeutic devices is extremely limited. For conditions where direct stimulation of the cortex may alleviate symptoms, such as stroke, clinical trials testing electrical cortical stimulation (CS) have produced mixed effects. These protocols may be less refined than other types of neurostimulation because basic physiological effects are not well understood, and because responses in the cortex are less predictable than other types of neurostimulation (e.g. to nerves). The following dissertation outlines experiments in non-human primates designed to document the physiological and behavioral effects of two types of CS. First, we adopt a tonic form of CS common among clinical trials, transcranial direct current stimulation, and demonstrate how polarity and dose influence neural activity. Second, we test two forms of phasic CS: one that is timed relative to unilateral hand movements in a reaction time task, and another that is triggered by muscle activity. “Activity-dependent” CS such as these can be used to probe the functional roles of dynamic brain signals, or to induce plasticity. Our monkey model provides direct physiological evidence that is often lacking in human research, and reveals that, under certain conditions, CS produces repeatable changes in brain activity by facilitating or disrupting natural physiological processes. These insights may be useful towards the design of future CS-based therapies.