The role of the left posterior parietal lobule in top-down modulation on space-based attention: a transcranial magnetic stimulation study

Abstract

Converging evidence from neuroimaging as well as lesion and transcranial magnetic stimulation (TMS) studies has been obtained for the involvement of right ventral posterior parietal cortex (PPC) in exogenous orienting. However, the contribution of dorsal PPC to attentional orienting, particularly endogenous orienting, is still under debate. In an informative peripheral cueing paradigm, in which the exogenous and endogenous orienting can be studied in relative isolation within a single task, we applied TMS over sub-regions of dorsal PPC to explore their possible distinct involvement in exogenous and endogenous processes. We found that disruption of the left posterior intraparietal sulcus (pIPS) weakened the attentional effects of endogenous orienting, but did not affect exogenous processes. In addition, TMS applied over the right superior parietal lobule (SPL) resulted in an overall increase in reaction times. The present study provides the causal evidence that the left pIPS plays a crucial role in voluntary orienting of visual attention, while right SPL is involved in the processing of arousal and/or vigilance.

Figure 1

Schematic depiction of the stimuli and procedure

Figure 2

Results of Experiment 1. A: Mean reaction times for valid, intra, and inter conditions under both high and low cue validity. B: SAE and OAE under different cue validity conditions. Error bars indicate SEMs. “*” indicates P < 0.05 and “n.s.” indicates P > 0.05.

Figure 3

TMS sites relative to individual magnetic resonance images of one subject as extrapolated using a frameless stereotaxic system.

Figure 4

Results of Experiment 2. A: Mean reaction times for valid, intra, and inter conditions in left‐parietal stimulation group. B, C: SAE and OAE for left SPL stimulation, left pIPS stimulation, and no‐TMS condition. D: Mean reaction times for valid, intra, and inter conditions in right‐parietal stimulation group. E, F: SAE and OAE for right SPL stimulation, right pIPS stimulation, and no‐TMS condition. Error bars indicate SEMs. “*” indicates P < 0.05 and “n.s.” indicates P > 0.05.