Cat SI and SII optical responses to 25 Hz vibrotactile stimulation of the forepaws (2 subjects). A. View of the cortical surface, showing the vascular pattern and coronal (COR), ansate (ANS), and suprasylvian (SS) sulci. Exposed portions of SI and SII are indicated. Left hand column of Subject 1 and Subject 2 : Averaged difference images for responses evoked by (B) contralateral, (C) ipsilateral and (D) bilateral stimuli. Adjacent thresholded images of responses evoked by the three modes of stimulation – horizontal grid lines facilitate comparison of the position of loci of the evoked responses and are spaced 2 mm apart. Stimulus sites are indicated by figurines. Note that in both subjects, ipsilateral stimulation evokes a response posterior to the response evoked by contralateral stimulation. Scale bar is 2 mm. Orientation of images indicated by P (posterior), A (anterior), M (medial) and L (lateral) axes.