Potentials and limits to enhance cognitive functions in healthy and pathological aging by tDCS

Abstract

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that is increasingly used in research and clinical settings to enhance the effects of cognitive training. In our present review, we will first summarize studies using tDCS alone and in combination with cognitive training in older adults and patients with Alzheimer’s dementia (AD). We will also review one study (Meinzer et al., 2014c) that showed an improvement in cognitive performance during anodal tDCS over the left inferior frontal cortex in patients with mild cognitive impairment (MCI) which is regarded as a prodromal stage of AD. Although promising short-term results have been reported, evidence from randomized controlled trials (RCTs) with sufficient sample sizes is scarce. In addition, stimulation protocols (in terms of intensity, duration, and repetition of stimulation) that lead to sustained improvements in outcome measures relevant for daily life still remain to be established. Following, we will discuss modulating factors such as technical parameters as well as the question whether there are specific cognitive functions (e.g., learning, memory consolidation, executive control) which are more amenable to tDCS enhancement than others. Finally, we will highlight future directions and limitations in this field and emphasize the need to conduct RCTs to establish efficacy of interventions for activities of daily life for a given patient population.

Older adults get episodic memory boosting from noninvasive stimulation of prefrontal cortex during learning

“…There is evidence that NIBS influences motor (Zimerman et al, 2013) and cognitive functions (Hsu et al, 2015; Prehn and Floel, 2015) in physiological aging.…”

Adaptive Plasticity in the Healthy Language Network: Implications for Language Recovery after Stroke

“…Indeed, a large number of previous studies used tDCS to facilitate learning and consolidation in different motor and cognitive tasks in healthy subjects [61, 62]. In contrast to TMS, the tDCS intensity is usually not calibrated to the individual motor threshold but given at a constant intensity across subjects.…”

Effects of Anodal Transcranial Direct Current Stimulation and Serotonergic Enhancement on Memory Performance in Young and Older Adults

“…As no effective disease-modifying pharmacological intervention has been approved so far, the search for new strategies to maintain higher brain function throughout life and to prevent the progression of the 'AD-precursor', mild cognitive impairment (MCI), to full-blown dementia is of major economic and medical importance (Mangialasche et al, 2010). Cognitive training (Anguera et al, 2013) and non-invasive brain stimulation techniques, such as anodal transcranial direct current stimulation (atDCS; Prehn and Floel, 2015), might offer exciting opportunities for enhancing brain function. atDCS, in particular, may help to overcome reduced brain responsiveness to cognitive training in aging, as it modulates post-synaptic connections analogous to long-term potentiation (LTP; Liebetanz et al, 2002) and has been shown to improve learning and memory in young and older healthy subjects by our group and others (Miniussi et al, 2013;Coffman et al, 2014;Shin et al, 2015).…”

“…These effects in healthy subjects and its excellent safety profile (Fregni et al, 2015) have encouraged the use of tDCS also after stroke and in neurodegenerative disease (Floel, 2014;Prehn and Floel, 2015). For instance, atDCS has been successfully applied to enhance language training outcome in post-stroke aphasia (Floel et al, 2011;Meinzer et al, 2016).…”

“…In AD patients, Ferruci et al, (2008) and Boggio et al, (2009) demonstrated in small pilot studies that episodic memory performance can be enhanced by atDCS administration over the dorsolateral prefrontal, temporal, and temporoparietal cortex. Effect sizes, however, were only small to moderate and producing sustained improvements of training success remains challenging (Prehn and Floel, 2015). Different approaches to reinforce and prolong the effects of atDCS have been suggested.…”