Sensorimotor cortex reorganization in subacute and chronic stroke: A neuronavigated TMS study

Abstract

The integrity of the corticospinal system is an important biomarker for recovery from stroke. However, mapping the topography of the corticospinal system in subacute stroke is not trivial and how it changes over the course of recovery is poorly understood. We intend to use a transcranial magnetic stimulation (TMS) based mapping approach to quantify the topographic landscape of corticospinal activation in the ipsi- and contralesional sensorimotor cortices in the subacute and chronic phase of stroke. Mapping was conducted before (PRE) and after (POST), intervention in 10 chronic subjects and 8 subacute subjects. Reorganization was quantified in a unique way by dissociating reorganization attributed to changes in the expanse (area) of the sensorimotor territory, from that attributed to changes in the robustness of the activation (amplitude). In doing so, we observed differences in reorganization in the subacute and chronic stages indicating that recovery in different stages may not be guided by similar neurophysiological mechanisms of neuroplasticity.

Figures

Figure 1

A graphical depiction of the analysis of MEP maps showing calculation of: (A) MEP signal and peak-to-peak amplitude; (B) neuronavigation data; (C) a stem plot of MEP amplitudes at each stimulation site; (D) cubic interpolation of MEP maps (5mm mesh); (E) creation of a contour surface map.

Figure 2. Single Subject Data

MEP maps for the first dorsal interosseous (FDI) muscle in a representative subacute stroke subject (ipsilesional hemisphere (left), contralesional hemisphere (middle)) and chronic subject (ipsilesional hemisphere (right), acquired PRE (top row), and post (bottom row) intervention. X, Y axes represent medial-lateral and anterior-posterior directions, respectively. MEP amplitude is presented in microvolts (uV) on the Z axis. Ipsilesional changes in the subacute subject are characterized by increased amplitude and area, while chronic subject map shows decreased amplitude over a similar area.

Figure 3. Group Mean Data

MEP map assessments in terms of map mean amplitude (top) and area (bottom). Note the different patterns of change between hemispheres and groups. Only the ipsilesional hemisphere of the subacute group changes in both amplitude and area.