Assessing the Role of the Left Dorsal Frontal Cortex in Working Memory Guidance: Attentional or Mnemonic? A Neurostimulation Study

Abstract

Perceptual selection can be guided by the contents of working memory (WM). Neuroimaging and neuropsychological data point to a role of a fronto-parietal and fronto-thalamic networks in WM guidance. Here we assessed the effect of transcranial direct current stimulation of the left dorsal frontal cortex (lDFC) in a combined WM/attention paradigm. We asked the extent to which the lDFC is implicated in mnemonic and selective attention functions during WM guidance of behavior. Observers were asked to keep information in memory while searching for a visual target, while the validity of WM contents for the search task varied. We tested the effects of lDFC-tDCS on the strength of WM guidance of search, whether any tDCS effect is dependent on the amount of WM load, and whether lDFC-tDCS primarily influences how WM contents are retained, the process of selective attention in search task, or both. Consistent with prior behavioral findings, we found that (i) selection of items that matched the contents of WM was facilitated relative to non-matching items and (ii) this WM guidance effect was reduced when the level processing/cognitive load in WM was higher. Notably, across two experiments we found that lDFC-tDCS modulated WM guidance of visual selection in the context of high processing loads in WM. No effects of tDCS were observed in WM accuracy. These findings suggest that the role of the left dorsal frontal cortex in WM guidance is associated with selective attentional control rather than mnemonic processing.