Transcranial direct current stimulation (tDCS) of frontal cortex decreases performance on the WAIS-IV intelligence test

Abstract

Transcranial direct current stimulation (tDCS) modulates excitability of motor cortex. However, there is conflicting evidence about the efficacy of this non-invasive brain stimulation modality to modulate performance on cognitive tasks. Previous work has tested the effect of tDCS on specific facets of cognition and executive processing. However, no randomized, double-blind, sham-controlled study has looked at the effects of tDCS on a comprehensive battery of cognitive processes. The objective of this study was to test if tDCS had an effect on performance on a comprehensive assay of cognitive processes, a standardized intelligence quotient (IQ) test. The study consisted of two substudies and followed a double-blind, between-subjects, sham-controlled design. In total, 41 healthy adult participants completed the Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV) as a baseline measure. At least one week later, participants in substudy 1 received either bilateral tDCS (anodes over both F4 and F3, cathode over Cz, 2mA at each anode for 20 minutes) or active sham tDCS (2mA for 40 seconds), and participants in substudy 2 received either right or left tDCS (anode over either F4 or F3, cathode over Cz, 2mA for 20 minutes). In both studies, the WAIS-IV was immediately administered following stimulation to assess for performance differences induced by bilateral and unilateral tDCS. Compared to sham stimulation, right, left, and bilateral tDCS reduced improvement between sessions on Full Scale IQ and the Perceptual Reasoning Index. This demonstration that frontal tDCS selectively degraded improvement on specific metrics of the WAIS-IV raises important questions about the often proposed role of tDCS in cognitive enhancement.

Low-Intensity Transcranial Current Stimulation in Psychiatry

“…Though claims that tCS improves brain function have been made (47)(48; 49), stimulation may also impair cognition (70). It may induce a functional “trade-off”, improving a single cognitive function at the cost of impairing another.…”

“…Specific electrode configurations may also be associated with adverse cognitive effects. Several studies described learning and working memory impairments when the tDCS cathode was applied over the parietal lobe or cerebellum (73; 74), and another found reduced cognitive performance when the tDCS anode was placed over the DLPFC (i.e., the configuration used by the vast majority of tDCS studies) (70). Worsened working memory has also been reported after use of a commercial tDCS device (75).…”

Transcranial stimulation over the left inferior frontal gyrus increases false alarms in an associative memory task in older adults

“…Our finding that tDCS led to decreased memory performance in a task where performance is typically low may explain why tDCS effects on cognition have been mixed in the past [47,48]. Using anodal stimulation, some studies have found null effects on cognition [22,23], whereas others have shown decreased cognitive performance [24,27]. The moderating influences of baseline performance may influence when tDCS improves cognition, such as when only adults with a high level education show benefits in working memory performance [3].…”

“…Although not all studies have focused exclusively on memory in older adults, there is a growing body of literature to suggest that tDCS does not universally improve cognition. For instance, aside from studies that have found no effects of tDCS on learning and memory performance [22,23], application of tDCS has decreased performance in target detection [24], working memory [25,26], and general intelligence tasks [27]. Thus, it is important to study the delineation of conditions under which cognition improves because of stimulation rather than suffers from it.…”

Novel Neuromodulation Techniques to Assess Interhemispheric Communication in Neural Injury and Neurodegenerative Diseases

“…This technique has been tested in humans as well as monkey and rats (Baker et al, 1995; Notturno et al, 2014; Lee et al, 2015; Sellers et al, 2015; Yoon et al, 2016). Similar to TMS studies discussed in earlier sections, the alteration in interhemispheric interaction following these disease states can be investigated also by using tDCS.…”