Figure 1.

Auditory and somatosensory fields in the insula. (A) Photographic record showing the most lateral placement of the epipial recording array in relation to bregma and the superior cerebral veins (arrowheads). (B) A transparent scaled template of the array was used to establish electrode locations in relation to underlying vasculature. AEP were then plotted in register with these electrode locations. Blue traces indicate responses in the IAF and black traces in the AAF. Representative AEPs (green circled traces) in both IAF (a) and AAF (b) consisted of a typical biphasic, positive/negative sharp wave (insert; P1/N1). The AEP in IAF was of smaller amplitude and shorter poststimulus latency than that recorded in AAF. (C) Topographical map reflecting the normalized amplitude distribution at the poststimulus latency of the P1 (earliest component, see insert). Note here that IAF was 1.85 mm lateral and 2.91 mm caudal to the center of AAF (50% amplitude iso-potential contours shown as dashed lines). (D) Electrical stimulation of forepaw yielded a focal SEP response that partially overlapped IAF, but was centered more caudally and is labeled the ISF (forepaw). (E) Electrical stimulation of hindpaw evoked an SEP that was shifted more caudal than the forepaw response (ISF hindpaw). For anatomical reference, a template of somatosensory representations derived from a more extensive mapping study of primary, secondary, and the lateral insular somatosensory cortex (Benison et al. 2007) is superimposed on the maps of (D) and (E) and subsequent figures.