We are working on three projects at the moment.
1- Plasticity in the undamaged hemisphere following motor cortical infarct
A stroke is a vascular lesion within the brain. Following a stroke located in the motor cortex, patients have several deficits including loss of upper extremity function. However, patients undergo substantial motor recovery in the weeks and months following the lesion. One hypothesis, for which there is now remarkable support, is that the recovery is dependent upon adaptive reorganization of intact, remaining brain structures. The changes in the hemisphere that had sustained the lesion (ipsilesional) are generally believed to be beneficial to the recovery. Conversely, the role of the reorganization that occurs in the hemisphere opposite to the lesion (contralesional) is controversial. Some studies conclude that plasticity in that hemisphere supports recovery, while others conclude that it actually interferes with it.
The goal of the present project is to study the nature of the reorganization in the contralesional hemisphere in order to understand how it can either participate or interfere in recovery. We will record neurons in various contralesional cortical areas in macaque monkeys using electrode arrays while they perform a motor task. We will identify changes of the neural activity that are related to the recovery of the impaired limb. This information will be of great value for the development of experimental protocols modulating brain activity to favor beneficial plasticity in humans after stroke. Because the greatest contralesional plasticity is often observed in individuals with the highest impairments after stroke, understanding this reorganization will be particularly useful for our care of these patients, for whom we currently have the fewest treatment options to offer.
2- The effect of rehabilitative training on the reorganization of the contralesional cortex following ischemic lesions in the rat
This project is also related to the role of the contralesional (CL) hemisphere in the recovery from stroke. In the proposed experiments, we investigate mechanisms through which rehabilitation affects plasticity and favors recovery. In this project, we combine sophisticated electrophysiological and neuroanatomical methods that are currently used in my laboratory with the well-established rehabilitative training protocol in rats developed by our collaborator Dr. Corbett at the University of Ottawa.
Following a stroke, the contralesional hemisphere undergoes some changes and in some cases, can contribute to the recovery of the paretic limb (Biernaskie et al., 2005). The role of the contralesional hemisphere appears to be affected by lesion size. Inhibition of the contralesional cortex in rats that recovered from large lesions induced more deficits in the paretic limb than in control rats or animals that recovered from small lesions. We know that rehabilitative training affects reorganization of the ipsilesional cortex in both animals and humans. What is the effect of rehabilitation on cortical reorganization in the CL hemisphere? Can rehabilitation change the role of the CL hemisphere in recovery of the paretic limb?
3- The effect of cortical interactions on motor output by the primary motor cortex
M1 receives numerous inputs from other cortical areas, in particular from the premotor cortices and the primary somatosensory cortex (S1). Currently, little is known on how these cortical connections contribute to the planning and regulation of movements. The general objective of our research program is to investigate the influence of cortical inputs from distant cortical areas on M1 and the role of these areas in the control of hand and arm movements. In the present set of experiments, we will focus on the topographic specificity of cortical inputs in M1 and how these inputs modulate the corticospinal outputs of M1.
In capucin monkeys, we will study the inputs of four cortical areas, the supplementary motor area (SMA), the dorsal and ventral premotor areas (PMd and PMv), and S1. We will investigate the topographic specificity of the major inputs in M1 and the modulatory effect of cortical inputs on M1 corticospinal outputs. Do do so, we will use a combination of neuroanatomical tracers, intracortical stimulation protocols using chronic electrode arrays implanted in M1 and the four distant cortical areas and recordings of electromyographic (EMG) activity forearm muscles.
We are looking for students and post-doctorate fellows to join our team, participate in these current projects or initiate new projects.