[Update 5/15/15 More or less debunked, at least a much better understanding of the anomalies of this particular study, from Nathan Whitmore’s rebuttal.] Would only now like to see this replicated with tDCS applied during testing. i.e. In this study tDCS was administered prior to the test (‘offline’ as opposed to ‘online’). But for those of us who are looking to tDCS for potential cognitive enhancement, this is a significant study. Posted to Reddit by Gwern!
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.
Source: “Transcranial Direct Current Stimulation of Frontal Cortex Decreases Performance on the WAIS-IV Intelligence Test”, Sellers 2015 : tDCS
This is to be expected.
Based on a comparison of tDCS, tACS, tRNS, and tACS found in the book, The Stimulated Brain – Cognitive Enhancement Using Non-Invasive Brain Stimulation (Page 38, Figure 2.1) edited by Roi Cohen Kadosh. [https://thebrainstimulator.net/faq/]: tDCS increases GABA and decreases Glutamate, while increasing BDNF. While tRNS increase glutamate signaling.
Thus, I would expect tDCS to impair performance on the Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV) precisely because speed of information processing is an important parameter. Increasing GABA and decreasing Glutamate signaling would significantly impair speed of information processing. Increasing GABA while decreasing Glutamate would be expected to reduce anxiety, help improve sleep. Increasing BDNF may reduce depressive symptoms while improving long-term memory.
tRNS on the other hand may improve performance on the Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV) since Glutamate signaling is enhanced.
Thanks for your comment Romeo. Sounds like you’d be a welcome contributor to the tDCS subReddit!
Thanks. I just jointed Reddit’s tDCS subReddit. I am very interested in the clinical use of low-current brain stimulation aside from its possible nootropic-like aspects.
You know the GABA/Glutamate relationship to tDCS is not very well understood in the DIY community. If you have any insights to share I’d be happy to publish them here, or perhaps you have a blog where you’re covering this? Oh wait… I just checked your email address which led to Definitive Mind. I’ll check it out!
Sorry, I haven’t posted there is a couple of years. Have been too busy. I’ll probably update the site in the next year.
In the meantime, thanks for your site and information.