The role of the contralesional hemisphere during the recovery after a stroke : a short review

Background. The cerebral plasticity plays a critical role after damage to central nervous system (CNS), with functional reshaping that underlies the clinical recovery [1]. Neural substrates of “post-lesional” brain plasticity are under intense study, since knowledge of this phenomenon can lead to an appropriate rehabilitation treatment and a successful functional recovery. After a stroke, among the mechanisms of cortical reorganization, there is the increase of activity of contralesional hemisphere [2], as assessed by longitudinal studies using functional imaging and direct cortical stimulation. The role of the unaffected hemisphere during recovery after a stroke is still debated. The aim of this study is to assess how and when the contribution of contralesional hemisphere influences the functional recovery after a cerebrovascular event. Materials and methods. A search was performed through the database PubMed, considering the publications between 2004 and 2015. The following key words were used: "stroke", "recovery", "contralesional", "functional magnetic resonance imaging (fMRI)", "transcranial magnetic stimulation (TMS)", with several search strings. All studies concerning adults after their first ischemic or hemorrhagic stroke, within the first six months after the event, were collected. Twenty-four studies were included and a qualitative analysis of the selected studies was performed. Discussion. Most of the recent studies confirm that, in the acute phase after a stroke, the hyperactivity of the unaffected hemisphere appears to depend on the extension of the lesion, on the severity of the clinical injury and on the interval from the cerebrovascular event. The underlying pathophysiological mechanism represents an adaptive compensation and may enhance functional recovery. After the third month after a stroke, the persistence of contralesional hyperactivity appears to be a maladaptive process, because it may slow down a functional recovery. Since the unaffected hemisphere is activated also when the ipsilesional limbs are moving, the rehabilitation treatment should respect the different phases of cerebral plasticity and should avoid “overuse”. After a cerebrovascular event, in fact, neurological deficits are caused not only by the lesion, but also by the same mechanisms that underlie the functional recovery, such as diaschisis. References. (1) Daffau H. Brain plasticity: from pathophysiological mechanisms to therapeutic applications. Journal of Clinical Neuroscience 2006 Vol 13, 885–97. (2) Grafkes C. Ward N.S. Cortical reorganization after stroke: how much and how functional? The Neuroscientist 2014 Vol. 20 (1), 56 –70.