Cortical magnetic responses during linear apparent self motion

Abstract

Electrophysiological studies in monkeys identified region of cerebral cortex that receive vestibular inputs including poserior part of the insula (parieto-insular vestibular cortex: PIVC), portions of the intraparietal sulcus (area 2~). and the central sulcus (area 3aV). Some past studies demonstrated that sensations of apparent whole body rotation also activate these regions. The information of whole body rotation is received by semicircular canals. On the other hand, the information of whole-body linear motion is received by otolith receptors, and its cortical processes are still unclear. In this study, the cortical sites that process sensations of linear apparent self motion (linear vection) were studied using neuromagnetic measurements. Brain magnetic fields evoked by visual motion stimuli were measured in 7 healthy volunteers (6 males, 22-34 years, right-handed, normal or corrected-to-normal vision), who reported they experienced sensation of apparent motion during measurements. Measurements of magnetic fields were carried out using 122ch whole-head neuromagnetometer (Neuromag-122TM) in a magnetically shielded room. Following white expanding stimuli (maximum size: 21*10.5 degrees) were presented on the black screen. (a) a rectangle expanding at 5.3 &g/s, 71.4 %, (b:vection stimulus) a rectangle expanding at 26.5 deg/s, 14.3 8, (c: control stimuli) a circle expanding at 5.3 deg/s, 14.3 %. The activated cortical areas were determined by first localizing single equivalent current dipoles (ECDs) in various local regions of a spherical head model. Among the calculated ECDs, those having a goodness-of-fit > 80% and with a 95%-confidence volume < 2000 mm3 were selected. The localization of ECDs was based on the spherical conductor model, which takes into account the volume current within the sphere. For both the vection and the control stimuli, the activation of post-central gyms (100 200 ms), infero-posterior temporal lobe (300 500 ms), lingual/fusiform gyrus (300 500 ms) were found. On the other hand, activations in posterior insula (300 400 ms), posterior operculum (400 500 ms). parietal lobule (300 500 ms), pre-central gyrus (300 400 ms), superir temporal gyms (400 500 ms) were observed for only vection stimulus. These areas are recognized as human analogs of vestibular cortex identified by former studies in monkey. The results also suggest these areas integrate multi-modal information.