The causal role of the left parietal lobe in facilitation and inhibition of return

Abstract

Following non-informative peripheral cues, responses are facilitated at the cued compared to the uncued location at short cue-target intervals. This effect reverses at longer intervals, giving rise to Inhibition of Return (IOR). The integration-segregation hypothesis (Lupiáñez, 2010) suggests that peripheral cues always produce an onset-detection cost regardless the behavioral cueing effect that is measured - either facilitation or IOR. In the present study, we used transcranial magnetic stimulation (TMS) to investigate the causal contribution of this detection cost to performance. We used a cueing paradigm with a target discrimination task that was preceded by a non-informative peripheral cue. The presence-absence of a central intervening event was manipulated. Online TMS to the left superior parietal lobe (compared to an active vertex stimulation) lead to an overall more positive effect (faster responses for cued as compared to uncued trials), by putatively impairing the detection cost contribution to performance. The data revealed a strong association between overall RT and the TMS effect, and also between overall RT and the integrity of the first branch of the left superior longitudinal fascicule. These results have critical implications not only for the open debate about the mechanism/s underlying spatial orienting effects, but also for the growing literature demonstrating that white matter connectivity is crucial for explaining inter-individual behavioral variability.

Keywords: Facilitation; Inhibition of return (IOR); Superior longitudinal fasciculus (SLF); Superior parietal lobe (SPL); Transcranial magnetic stimulation (TMS).