P206 Cross-hemispheric frontoparietal desynchronization impairs the visual-spatial working memory in humans

Abstract

Introduction Multiple studies indicated the left and right prefrontal cortex (PFC) and posterior parietal cortex (PPC) as anatomical substrates of the spatial working memory (i.e. frontoparietal memory network), however, the exact functional connectivity between these areas remains uncertain. This is partly due to the limitations of the applied neuroimaging methodologies, which are correlative in nature, as well as the classical brain stimulation approaches that are mostly operate within the limited number of neocortical sites. Objectives Here, we are taking advantages of the novel multichannel transcranial alternating current stimulation (tACS) method in order to investigate the role of phase connectivity between the frontoparietal regions in the left and right hemispheres that are commonly associated with the visual-spatial working memory related behavior. Materials & methods Fifteen healthy volunteers (11 females, age range: 19–28 years) participated in this double-blinded, placebo-controlled, randomized, crossover study. Each of them completed a 2-back visual-spatial working memory test during tACS and sham stimulation. Multichannel stimulation was applied at an intensity of 1 mA peak-to-baseline with a frequency of 6 Hz over the left PFC and PPC versus the right PFC and PPC. The working memory performance was estimated according to the signal detection theory as follows: d ′ = Z (“hit rate”) − Z (“false alarm rate”); and compared using the paired t-test. Results We observed the significant decrease in working memory performance during the desynchronization of the left and right frontoparietal regions in comparison to the control: d ′ control = 2.58 ± 0.12 (mean ± s.e.m.) and d ′ desynch = 2.34 ± 0.11 ( T (14) = 2.44, p = 0.03). No significant differences in the skin sensations and phosphenes were perceived according to the post-session written reports. Conclusion The efficiency of visual-spatial working memory in humans depends on the precisely calibrated phase connectivity within the frontoparietal network. Desynchronization of these relationships leads to the significant impairment of working memory performance.