The goal of the current research is to establish whether Hebbian-type cortical stimulation enhances motor cortex reorganization and associated behavioral gain and whether this translates into structural long-term plasticity and maintenance of the behavioral gain in patients post-stroke (recently completed R21).
Over the past fifteen years, the lab has also been exploring the role of the unaffected hemisphere in recovery after stroke. Activation of bilateral sensorimotor cortices in stroke patients moving their affected hand suggest that ipsilateral motor projections may play a role in recovery. Our own studies have contributed to this contemporary body of knowledge by showing for the first time that contralesional M1 (motor cortex of the hemisphere not affected by the stroke) activation occurs with a strictly unilateral performance of the affected hand. In these studies, we used for the first time electromyographic recording during motor performance in the fMRI experiment to control for mirror movements of the non-affected hand. These results support the notion that activation in contralesional M1 most likely reflects a reorganizational process, a claim that is in line with evidence from animal work (see Neurology 2005). However, we also demonstrated that even in healthy subjects, as the demand on precision of a movement increases, a bilateral activation of motor cortices is seen (see J Neurophysiol 2014). This finding has significant implications for the field of motor control but also for the interpretation of the results in stroke patients.
These results prompted researchers to explore mechanisms of contralesional M1 reorganization in stroke patients. Our data contributed to the existing evidence by demonstrating that first, the balance of excitatory and inhibitory activity in neuronal circuits was shifted towards excitatory activity, thereby suggesting that regulation of excitatory and inhibitory neurotransmitter systems may play a role early in the reorganization process in contralesional M1 and may support functional recovery (1-6 weeks) early after stroke. This notion is further supported by the second finding of our studies, in which we demonstrated a close association between increased excitability of contralesional M1 and good recovery of hand function. The goal of the current NIH R01 () funded longitudinal study is to determine prospectively the role of the contralesional M1 in the recovery of stroke. The results generated from this study will be used to develop patient tailored TMS protocols that target the contralesional M1 depending on its role.
We also study the impact of behavior/motor practice in shaping motor representation. We have made seminal contributions to the understanding of development of motor cortex in man. We demonstrated that in the absence of behavior in the upper extremities as seen in adults with severely compromised hand function since early childhood and compensatory foot use an abnormal somatotopic organization of the motor cortex develops. In these subjects’ M1 an additional foot representation is located in an area usually dedicated to the hand representation (see PNAS 2009).
The lab had uninterrupted NIH funding over the past 10 years and the PI has authored 46 peer-reviewed manuscripts. The PI’s ‘h-index’, a metric that captures not only the number of a scientist’s publications, but also their impact, is 22 (the index representing that number of a scientist’s papers that has received at least as many number of citations). Graphical representation of the number of my published manuscripts conveys substantial and sustained productivity. The increasing number of citations of our work from year to year speaks to its relevance and genuine impact upon Neurorehabilitation Science as well as the larger scientific community.