Asymmetry of Parietal Interhemispheric Connections in Humans

Abstract

Visuospatial abilities are preferentially mediated by the right hemisphere. Although this asymmetry of function is thought to be due to an unbalanced interaction between cerebral hemispheres, the underlying neurophysiological substrate is still largely unknown. Here, using a method of trifocal transcranial magnetic stimulation, we show that the right, but not left, human posterior parietal cortex exerts a strong inhibitory activity over the contralateral homologous area by a short-latency connection. We also clarify, using diffusion-tensor magnetic resonance imaging, that such an interaction is mediated by direct transcallosal projections located in the posterior corpus callosum. We argue that this anatomo-functional network may represent a possible neurophysiological basis for the ongoing functional asymmetry between parietal cortices, and that its damage could contribute to the clinical manifestations of neglect.

The time course for visual extinction after a ‘virtual’ lesion of right posterior parietal cortex

“…This is also consistent with our finding showing that left-sided extinction errors peaked late around 20-30 min after stimulation. The findings fit with models arguing for mechanisms of interhemispheric competition with a right hemisphere advantage (Hilgetag et al, 2001;Kinsbourne, 1977;Koch et al, 2011), indicating that abnormal interhemispheric interactions likely mediate our observed asymmetry of visuospatial functions (Battelli, Alvarez, Carlson, & Pascual-Leone, 2009;Müri et al, 2002;Plow et al, 2014). An alternative explanation for our results is that right-PPC stimulation induced breakdown of right PPC functions together with a breakdown of left PPC functions, conveyed through callosal inhibition.…”

Spatiotemporal Dynamics of Bimanual Integration in Human Somatosensory Cortex and Their Relevance to Bimanual Object Manipulation

“…Thus, interhemispheric somatosensory inhibition in SII peaked later and lasted over a longer range of C-T intervals compared with interhemispheric motor inhibition, regardless of whether the latter is mediated directly via connections between MI (Ferbert et al, 1992) or via connections between homologous PPC (Koch et al, 2011). In contrast to MI, SII serves as a higher-order area, i.e., it integrates information from other somatosensory areas.…”

Tractography‐based parcellation of the human left inferior parietal lobule

“…Additionally, clinical studies have indicated that left-hemispheric lesions in the IPL may cause Wernicke's aphasia and primary progressive aphasia, since the language system is mostly left-lateralized (Amici et al, 2006;GornoTempini et al, 2004;Mesulam, 2001;Ojemann, 1979). Recently, asymmetry has also been identified in human parietal interhemispheric anatomical connections (Koch et al, 2011). Given this asymmetry and the fact that Mars et al (2011) found extensive localization within the RIPL, exploring the functional and anatomical subdivisions of the LIPL is necessary.…”