Value and Efficacy of Transcranial Direct Current Stimulation in the Cognitive Rehabilitation: A Critical Review Since 2000

Abstract

Non-invasive brain stimulation techniques, including transcranial direct current stimulation (t-DCS) have been used in the rehabilitation of cognitive function in a spectrum of neurological disorders. The present review outlines methodological communalities and differences of t-DCS procedures in neurocognitive rehabilitation. We consider the efficacy of tDCS for the management of specific cognitive deficits in four main neurological disorders by providing a critical analysis of recent studies that have used t-DCS to improve cognition in patients with Parkinson's Disease, Alzheimer's Disease, Hemi-spatial Neglect, and Aphasia. The evidence from this innovative approach to cognitive rehabilitation suggests that tDCS can influence cognition. However, the results show a high variability between studies both in terms of the methodological approach adopted and the cognitive functions targeted. The review also focuses both on methodological issues such as technical aspects of the stimulation (electrode position and dimension; current intensity; duration of protocol) and on the inclusion of appropriate assessment tools for cognition. A further aspect considered is the optimal timing for administration of tDCS: before, during or after cognitive rehabilitation. We conclude that more studies using common methodology are needed to gain a better understanding of the efficacy of tDCS as a new tool for rehabilitation of cognitive disorders in a range of neurological disorders.

Limits to tDCS effects in language: Failures to modulate word production in healthy participants with frontal or temporal tDCS

“…However, cognitive effects are far more complex and unpredictable (Horvath, Forte, & Carter, 2015a). This is in part because tDCS effects interact with ongoing cortical activity (see Silvanto, Muggleton, & Walsh, 2008), as indicated by the general effectiveness of tDCS in patient samples (for review, see Cappon, Jahanshahi, Bisiacchi, Turner, & Paul, 2016; de Aguiar et al., 2015). It may therefore be that tDCS can modulate cognition in pathological brains where excitability or processing capacity is unusually low or dysfunctional, but not in healthy brains where neuronal excitability is operating at optimal levels.…”

Transcranial direct current stimulation alters functional network structure in humans

“…Transcranial direct current stimulation1,2,3,4,5 (tDCS) has been widely used in the neurosciences6,7,8,9 for decades. This is so because interfering techniques like tDCS that are assumed to directly modulate neuronal activity are extremely promising for both basic and applied research as they allow for addressing research questions on the causal relationships between brain states and behaviour10,11,12.…”

Transcranial Direct Current Stimulation as an Alternative Treatment in Patients with Alzheimer's Disease

“…To date, tDCS has been shown to have beneficial effect in numerous diseases including major depressive disorder [3], pain [4,5], stroke [6,7], drug addiction [8], refractory epilepsy [9], focal hand dystonia [10], and other degenerative disease [11].…”