Research Interests

My research interests span basic research on the mechanisms of motor control and motor learning and understanding of motor impairment under neurological disease.

One of my main research interests is stroke, a leading cause of disability affecting hundreds of thousands of Americans each year. I use a combination of carefully-tuned behavioral paradigms, quantitative methods, and robotics to tease apart the mechanisms behind the different motor symptoms after stroke. As a postdoctoral fellow at Johns Hopkins, I worked on two studies about motor control after stroke:

Motor learning and control in the acute vs. chronic stage after stroke

Abnormal synergies have been thought to be responsible for impaired control of active movement. In contrast to this idea, I recently showed that subacute stroke patients (<3 months after stroke) display markedly worse arm reaching kinematics compared to chronic stroke patients (>6 months after stroke) with similar Fugl-Meyer scores (a metric heavily based on abnormal synergies). This suggests a dissociation between abnormal synergies and movement control.

The effect of abnormal resting postures on active movement control

Abnormal resting postures are a prominent sign of stroke yet the mechanisms behind them are not well understood. Are these postures simply the resting points of the abnormal synergies which may impede active movement, or are they driven by a separate mechanism?

To begin tackling this question, I systematically mapped (involuntary) resting postural force biases of stroke patients on a 2D plane, and found that these biases are, like abnormal synergies, reduced by providing arm support. Moreover, these biases scaled with the Fugl-Meyer score, a synergy-based measure.

However, found that these resting postural forces did not affect reaching movements to or from positions of high resting postural abnormality. Instead, they only seemed to switch on after the movement was over, affecting the control of actively holding still perturbations. This suggests that the dissociation between the control of reaching and holding still - well-studied in the literature - is preserved in hemiparesis.

Persistence of motor adaptation against the passage of time

The motor system can implicitly learn to adjust its motor commands in response to errors. What are the mechanisms behind this adaptation process? Using time delays, I dissected motor adaptation into two qualitatively distinct components: one that decays rapidly within a minute, and one that is temporally-persistent.

I found that savings, the faster relearning of a previously learned but forgotten adapted state, is attributable to the temporally-labile component. In another study, I showed that the motor adaptation deficits of patients with cerebellar degeneration are specifically due to compromised temporally-stable adaptation, with temporally-labile adaptation apparently intact. This finding explained differences in adaptation of cerebellar patients across different studies, and may provide strategies to optimize learning in these patients.