Spatio-temporal updating in the posterior parietal cortex

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 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. We demonstrate increased fMRI activation in the left posterior parietal cortex when human participants adopted a crossed hands posture with their eyes closed. When participants performed tactile temporal order judgments (TOJs), 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 (IPS) (Wada et al., 2011). We then examined connectivity of the IPS to determine the functional anatomy of the arm crossing effect, as well as connectivity using a seed region in the posterior cingulate cortex to evaluate default mode network (DMN) for comparison. The regions showing connectivity with the IPS overlapped with regions within the DMN but the IPS also showed connectivity with other brain areas within the frontoparietal control network (Ora et al., 2012). The IPS, which can be considered a gateway connecting the DMN to the frontoparietal control network, may therefore be critically involved in monitoring limb position and in spatio-temporal binding when serial events are delivered to the limbs.