Spatio-Temporal Updating in the Left Posterior Parietal Cortex

Makoto Wada,Charles Spence,Hiroki Ora,Shiro Ikegami,Kouji Takano,Kenji Kansaku,Angela Sirigu

doi:10.1371/journal.pone.0039800

Abstract

Adopting an unusual posture can sometimes give rise to paradoxical experiences. For example, the subjective ordering of successive unseen tactile stimuli delivered to the two arms can be affected when people cross them. A growing body of evidence now highlights the role played by the parietal cortex in spatio-temporal information processing when sensory stimuli are delivered to the body or when actions are executed; however, little is known about the neural basis of such paradoxical feelings resulting from such unusual limb positions. Here, we demonstrate increased fMRI activation in the left posterior parietal cortex when human participants adopted a crossed hands posture with their eyes closed. Furthermore, by assessing tactile temporal order judgments (TOJs) in the same individuals, we observed a positive association between activity in this area and the degree of reversal in TOJs resulting from crossing arms. The strongest positive association was observed in the left intraparietal sulcus. This result implies that the left posterior parietal cortex may be critically involved in monitoring limb position and in spatio-temporal binding when serial events are delivered to the limbs.

Highlights

Adopting an unusual posture can sometimes give rise to paradoxical experiences. When people cross their arms over the body midline, the subjective rank ordering of successive unseen tactile stimuli delivered to both arms can be affected [1,2]
One should be somewhat cautious given the use of the uncrorrected threshold, but we focused on the left posterior parietal cortex in the analysis of variance (ANOVA) based on the results of the whole brain analyses (Fig. 1) and on the basis of other findings already published in the literature [3,4,5,6,7,8]
The participants took part in both left arm over right arm crossing (Crossed L) and right arm over left arm crossing (Crossed R) conditions, given previous findings indicating that people tend to report stronger paradoxical temporal order judgments in the Crossed L condition [6]

Summary

Introduction

Adopting an unusual posture can sometimes give rise to paradoxical experiences. For example, when people cross their arms over the body midline, the subjective rank ordering of successive unseen tactile stimuli delivered to both arms can be affected (often being reversed) [1,2]. Tactile stimulation of the right hand when placed across the body midline has been shown to give rise to increased activity in the right ventral intraparietal sulcus (VIP) in participants whose eyes are closed. The upper part of the left posterior parietal cortex is activated during the updating of limb position when people reach with their arm while their eyes are closed [5]. Recent neuroimaging studies have highlighted the involvement of the posterior parietal cortex or the temporoparietal junction when participants perform unimodal visual or tactile temporal order judgments (TOJs) [6,7,8]. The growing body of published evidence suggests the intimate involvement of the parietal cortex in spatio-temporal information processing in humans when sensory stimuli are delivered to the body surface or when actions are executed. That said, little is known about the neural basis of paradoxical feelings that may result when unusual static limb positions are adopted

Methods

Results

Conclusion