The role of the posterior parietal cortex on cognition: An exploratory study

Theta burst stimulation (TBS) is a form of repetitive transcranial magnetic stimulation (rTMS) that can be used to increase (intermittent TBS) or reduce (continuous TBS) cortical excitability. The current study provides a preliminary report of the effects of iTBS and cTBS in healthy young adults, to investigate the causal role of the posterior parietal cortex (PPC) during the performance of four cognitive functions: attention, inhibition, sequence learning and working memory. A 2 × 2 repeated measures design was incorporated using hemisphere (left/right) and TBS type (iTBS/cTBS) as the independent variables. 20 participants performed the cognitive tasks both before and after TBS stimulation in 4 counterbalanced experimental sessions (left cTBS, right cTBS, left iTBS and right iTBS) spaced 1 week apart. No change in performance was identified for the attentional cueing task after TBS stimulation, however TBS applied to the left PPC decreased reaction time when inhibiting a reflexive response. The sequence learning task revealed differential effects for encoding of the sequence versus the learnt items. cTBS on the right hemisphere resulted in faster responses to learnt sequences, and iTBS on the right hemisphere reduced reaction times during the initial encoding of the sequence. The reaction times in the 2-back working memory task were increased when TBS stimulation was applied to the right hemisphere. Results reveal clear differential effects for tasks explored, and more specifically where TBS stimulation on right PPC could provide a potential for further investigation into improving oculomotor learning by inducing plasticity-like mechanisms in the brain.