Non-invasive brain stimulation in Parkinson's disease: Exploiting crossroads of cognition and mood

- Cognitive dysfunctions and depression are common manifestations of PD.
- Non-invasive stimulation offers the potential to treat both symptoms concomitantly.
- Specific cognitive impairments of PD are improved by frontal rTMS and tDCS.
- rTMS over the DLPFC shows promise in alleviating depression in PD.
- Therapeutic and methodological considerations are discussed.

Cognitive impairments and depression are common non-motor manifestations in Parkinson's disease (PD). Recent evidence suggests that both partially arise via the same frontostriatal network, opening the opportunity for concomitant treatment with non-invasive brain stimulation (NIBS) techniques such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS).In this systematic review, we evaluate the effects of NIBS on cognition and/or mood in 19 placebo-controlled studies involving 561 PD patients. Outcomes depended on the area stimulated and the technique used. rTMS over the dorsolateral-prefrontal cortex (DLPFC) resulted in significant reductions in scores of depressive symptoms with moderate to large effect sizes along with increased performance in several tests of cognitive functions. tDCS over the DLPFC improved performance in several cognitive measures, including executive functions with large effect sizes. Additional effects of tDCS on mood were not detectable; however, only non-depressed patients were assessed. Further confirmatory research is needed to clarify the contribution that NIBS could make in the care of PD patients.