The effects of tDCS upon sustained visual attention are dependent on cognitive load

• Published in: Neuropsychologia Vol. 80; pp. 1 - 8
• Main Authors: Roe, James M., Nesheim, Mathias, Mathiesen, Nina C., Moberget, Torgeir, Alnæs, Dag, Sneve, Markus H.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 08.01.2016
• Subjects: Adult; Analysis of Variance; Attention; Attention - physiology; Cognition - physiology; Cognitive load; Female; Functional Laterality - physiology; Humans; Male; Multiple object tracking; Parietal Lobe - physiology; Photic Stimulation; Psychomotor Performance; Psychophysics; Reaction Time - physiology; Transcranial Direct Current Stimulation; Young Adult; Cognitive load; Transcranial direct current stimulation; Multiple object tracking; Attention
• ISSN: 0028-3932; 1873-3514
• DOI: 10.1016/j.neuropsychologia.2015.11.005

Transcranial Direct Current Stimulation (tDCS) modulates the excitability of neuronal responses and consequently can affect performance on a variety of cognitive tasks. However, the interaction between cognitive load and the effects of tDCS is currently not well-understood. We recorded the performance accuracy of participants on a bilateral multiple object tracking task while undergoing bilateral stimulation assumed to enhance (anodal) and decrease (cathodal) neuronal excitability. Stimulation was applied to the posterior parietal cortex (PPC), a region inferred to be at the centre of an attentional tracking network that shows load-dependent activation. 34 participants underwent three separate stimulation conditions across three days. Each subject received (1) left cathodal / right anodal PPC tDCS, (2) left anodal / right cathodal PPC tDCS, and (3) sham tDCS. The number of targets-to-be-tracked was also manipulated, giving a low (one target per visual field), medium (two targets per visual field) or high (three targets per visual field) tracking load condition. It was found that tracking performance at high attentional loads was significantly reduced in both stimulation conditions relative to sham, and this was apparent in both visual fields, regardless of the direction of polarity upon the brain’s hemispheres. We interpret this as an interaction between cognitive load and tDCS, and suggest that tDCS may degrade attentional performance when cognitive networks become overtaxed and unable to compensate as a result. Systematically varying cognitive load may therefore be a fruitful direction to elucidate the effects of tDCS upon cognitive functions. •The interaction of cognitive load and tDCS was examined during attentional tracking.•Tracking accuracy was reduced only under high cognitive load bilaterally.•Results indicate the importance of cognitive state in determining tDCS effects.