Projections on the cortical somatic I barrel subfield from ipsilateral vibrissae in adult rodents.

In adult rats and mice, ipsilateral projections to SI posteromedial barrel subfield (PMBSF) are demonstrated for mystacial vibrissae (sinus hairs). Mechanical stimulation with angular deflections in the 2-5 degrees range, elicits potentials in limited areas of SI whose geometric centers coincide for two homologous (contra- and ipsilateral) vibrissae. The cortical domains for two adjacent vibrissae overlap one another slightly. Phase reversal of potentials and unit discharges are also present within the cortex. Ablation of the SI area contralateral to the SI area under study completely abolishes the ipsilaterally projected potentials. It is proposed that ipsilateral responses are mediated via the corpus callosum with an extra delay of 4-5 msec, thus giving each hemisphere the opportunity to compare vibrissal information originating from the two mystacial pads.