No effect of parietal transcranial direct current stimulation (tDCS) on attention and memory

Switching between two tasks leads to switch costs not only for immediate performance but also for memory for task-relevant targets. For task-irrelevant distractors, however, we find a memory benefit. This reduced memory selectivity suggests that on switch trials when the appropriate task set is being reconfigured attention is broadened so that more distractors are encoded at the expense of targets. We tested the hypothesis that during task switching top-down cognitive control is exerted in order to attend to the targets and ignore the distractors. By disturbing attentional control, we should find a bigger effect of task switching in the sense of slower reaction times and reduced memory selectivity. By enhancing attentional control in contrast, we should find faster reaction times and higher memory selectivity. Furthermore, we wanted to investigate the role of bottom-up cognitive control. To this end, we stimulated the brain bihemispherically targeting two substrates of top-down and bottom-up cognitive control; left superior parietal lobe and right inferior parietal lobe, respectively. During task switching 60 participants underwent either “anodal left and cathodal right”, “anodal right and cathodal left”, or sham stimulation. There was no effect of tDCS on reaction times or accuracy rates during task switching. Neither did the groups differ in respect to their memory selectivity in a subsequent offline recognition test. The results question the effectiveness of the present tDCS-protocol for altering higher cognition.