Neurostimulation for Stroke Rehabilitation

Abstract

Neurological injuries such as strokes can lead to important loss in motor function. Thanks to neuronal plasticity, some of the lost functionality may be recovered over time. However, the recovery process is often slow and incomplete, despite the most effective conventional rehabilitation therapies. As we improve our understanding of the rules governing activity-dependent plasticity, neuromodulation interventions are being developed to harness neural plasticity to achieve faster and more complete recovery. Here, we review the principles underlying stimulation-driven plasticity as well as the most commonly used stimulation techniques and approaches. We argue that increased spatiotemporal precision is an important factor to improve the efficacy of neurostimulation and drive a more useful neuronal reorganization. Consequently, closed-loop systems and optogenetic stimulation hold theoretical promise as interventions to promote brain repair after stroke.

Keywords: brain-computer interfaces; closed-loop stimulation; neural plasticity; neuromodulation; neurostimulation; optogenetic stimulation; stroke.

FIGURE 1

Stimulation Paradigms to Induce Plasticity. Depiction of three main stimulation strategies used to induce plasticity. With repetitive stimulation, pre-synaptic neurons are activated directly and post-synaptic neurons are activated transsynaptically. With paired stimulation, the synchronization of pre- and post-synaptic populations is controlled directly by the stimulation of two points of the nervous system. Repetitive and paired stimulation can be applied in an open-loop manner, with no regard to current brain or behavioral state. In closed-loop approaches, however, the stimulation of a neuronal (post-synaptic) population can be precisely timed with neuronal activity (e.g., action potentials or EEG). These three different strategies all aim to induce coincidental activity in pre- and post-synaptic neurons with such a timing that would result in either LTP- or LTD-like effects, according to the rules of Hebbian STDP.