A selective working memory impairment after transcranial direct current stimulation to the right parietal lobe

Abstract

The role of the posterior parietal cortex in working memory (WM) is poorly understood. We previously found that patients with parietal lobe damage exhibited a selective WM impairment on recognition but not recall tasks. We hypothesized that this dissociation reflected strategic differences in the utilization of attention. One concern was that these findings, and our subsequent interpretation, would not generalize to normal populations because of the patients' older age, progressive disease processes, and/or possible brain reorganization following injury. To test whether our findings extended to a normal population we applied transcranial direct current stimulation (tDCS) to right inferior parietal cortex. tDCS is a technique by which low electric current applied to the scalp modulates the resting potentials of underlying neural populations and can be used to test structure-function relationships. Eleven normal young adults received cathodal, anodal, or sham stimulation over right inferior posterior parietal cortex and then performed separate blocks of an object WM task probed by recall or recognition. The results showed that cathodal stimulation selectively impaired WM on recognition trials. These data replicate and extend our previous findings of preserved WM recall and impaired WM recognition in patients with parietal lobe lesions.

Figure 1

(A) Trial design. During each trial, six pictures were presented (1000 ms/image), followed by a delay (1000 ms). During recognition blocks, a seventh probe image then appeared and participants judged whether it had been part of the memory set. During recall trials, participants were cued to say the names of all remembered items. (B) Session Protocol. After the electrodes were placed on the participant’s head, the session began. Participants first performed a block of practice trials during the anodal (A), cathodal (C) and sham (S) sessions. Electrodes were then removed and the first of four trial blocks of alternating trial types began.

Figure 2

Recall WM accuracy (left) and Recognition WM corrected recognition (hits-false alarms; right) for each condition (anodal, cathodal and sham). Lines in the right panel indicate significantly different pairwise comparisons, asterisks indicate a significance level of p < .05.