Figure 2. Auditory influences on somatosensory activity in the rostral suprasylvian sulcus (RSS).

Part ‘A’ illustrates, on the lateral view of the cat cerebral cortex, the location of the RSS, as well as its position (shaded gray on coronal sections) within the lateral bank of the rostral suprasylvian ectosylvian sulcus. The line/black dot represent the recording penetration and site (respectively) of a bimodal (B) and a subthreshold multisensory (C) neuron whose activity is depicted in subsequent parts. Part ‘B’ shows the activity of an RSS bimodal neuron to a tactile (ramp labeled ‘T’), auditory (square wave labeled ‘A’) and combined tactile-auditory stimulation. The scatter plot in ‘B’ shows, for the population of bimodal neurons, the relationship of activity elicited by tactile stimulation alone (x-axis) versus that evoked by the combined tactile-auditory stimuli (y-axis). The large majority of bimodal RSS neurons exhibited combined responses that plotted above the line of unity; although the magnitude of these responses was generally small (B: bar graph), several examples >100% response change were observed. Part ‘C’ shows the excitatory response of an RSS subthreshold multisensory neuron to a tactile, but no response to an auditory stimulus. However, when the stimuli were combined, the resulting response was significantly (p<0.05, paired t-test) different than that elicited by the tactile stimulus alone. The scatter plot (C) for the population of RSS subthreshold multisensory neurons shows the relationship of activity elicited by tactile stimulation alone (x-axis) versus that evoked by the combined tactile-auditory stimuli (y-axis). This result consistently plotted away from the line of unity and represented response magnitudes that often exceeded 50%, as displayed in the bar graph in ‘C.’