Noninvasive brain stimulation for Parkinson's disease

Abstract

In advanced Parkinson's disease (PD), the emergence of symptoms refractory to conventional therapy poses therapeutic challenges. The success of deep-brain-stimulation (DBS) and advances in the understanding of PD pathophysiology have raised interest in noninvasive brain stimulation as an alternative therapeutic tool. The rationale for its use draws from the concept that reversing abnormalities in brain activity and physiology thought to cause the clinical deficits may restore normal functioning. Currently the best evidence in support of this concept comes from DBS, which improves motor deficits, and modulates brain activity and motor cortex physiology, though whether a causal interaction exists remains largely undetermined. Most trials of noninvasive brain stimulation in PD have applied repetitive transcranial magnetic stimulation (rTMS) targeting the motor cortex. The current studies suggest a possible therapeutic potential of rTMS and transcranial direct current stimulation (tDCS), but clinical effects so far have been small and negligible regarding functional independence/quality-of-life. Approaches to potentiate the efficacy of rTMS include increasing stimulation intensity and novel stimulation parameters, which derive their rationale from studies on brain physiology. These novel parameters intend to simulate normal firing patterns or to act on the hypothesized role of oscillatory activity in the motor cortex and basal ganglia in motor control and its contribution to the pathogenesis of motor disorders.