Investigating the role of parietal and prefrontal cortices in spatial working memory using tDCS

Question – Working memory involves the temporary storage, processing, and manipulation of information. Previous studies have suggested that the posterior parietal cortex (PPC), and dorsolateral prefrontal cortex (DLPFC) are involved in spatial working memory, and spatial and object working memory, respectively. The aim of the present pilot study was to investigate whether modulation of the activity of the left PPC and the left DLPFC changes spatial, and object working memory performance. Transcranial direct current stimulation (tDCS) was used for this purpose. Based on past literature we expected to see improvement of both spatial and object working memory after tDCS of the left DLPFC as well as improvement of spatial working memory after tDCS of the left PPC.

Methods – Participants (n = 12) attended three experimental sessions with different stimulation conditions. Fifteen minutes of 1.5 mA anodal tDCS was applied over either the left PPC, left DLPFC or occipital lobe as control condition, beginning five minutes before the task. Participants were required to perform a 2-back spatial and object working memory task; i.e., they were required to pay attention to both objects and their location. Abstract objects were presented on either of an eight locations placed on a virtual circle around the centre of the screen. In addition to a 2-back object working memory task, occasionally participants were asked to indicate the location of the object they saw two screens previously. Performance in three different conditions was measured for analysis: (1) 2-back working memory task for the cases in which both cue and target objects were presented in the same location (OWM-same), (2) in different location (OWM-different) and (3) spatial working memory (SWM).

Results – Preliminary results showed that performance in the OWM-different condition was lower than OWM-same. There, however, was no significant different between different stimulation conditions.

Conclusions – These results suggest that anodal tDCS to the left PPC and left DLPFC might not be able to modulate spatial, and object working memory performance. Further studies are needed to investigate the differential role(s) of the DLPFC and PPC in spatial and working memory.