Orientation of attention and sensory gating: an evoked potential and reaction time study in cat.

Somesthetic-evoked potentials (SEPs) were recorded in eight cats trained to perform a reaction time task (RT). The preparatory period (PP) preceding the RT began with the cat placing its paw in a box and ended 1.5 s later with a paw-withdrawal signal, an imperative stimulus (IS). In experiment 1 (E1), the IS took the form of a vibration in the box, whereas in experiment 2 (E2) a tone was used. The SEPs were elicited by electrical stimulation delivered to the paw once per trial and at a different moment during the last second of each PP. The SEPs were recorded in the lemniscus medialis (LM), the centrum medianum (CM), and over the anterior suprasylvian gyrus (ASSG). During the PP of E1 (four cats), SEPs recorded in the CM and over the ASSG were found to be significantly depressed. No significant change was noted, however, in those recorded in the LM. No significant SEP depression was found in any of the structures in E2 (four cats). Comparison between the two experiments revealed notable differences at both the thalamic and cortical levels. Moreover, SEP depression diminished as the moment for the IS approached. While, in E1, this occurred in the CM and over the ASSG, in E2 it was found in the CM only. Lemniscal and thalamic SEP amplitude was found to be correlated with performance. These findings are discussed in terms of orientation of attention, discrimination, and sensory gating.