MODIFICATION OF THALAMIC AND CORTICAL ACTIVITY EVOKED DURING SENSORY CONDITIONING .1. LOCALIZATION OF RESPONSE AND VARIATION WITH WAKEFULNESS

Modifications of evoked responses in the freely moving cat were studied during sensory conditioning, using a brief tone as conditioned stimulus and brief stimulation of weak intensity to the cutaneous branch of the radial nerve as the unconditioned stimulus. No movement was observed; only modifications of electrophysiological responses were studied. Altogether 318 experiments were carried out. Changes occurred specifically in the cortical area (SI) and in the primary thalamic relay (VPL) of the afferent pathways concerned with the unconditioned stimulus. In cortical area SI they were localized in a posterior zone corresponding to the actual primary somatic area, and in the thalamus at the periphery of VPL, an associative region with somatotopic preference. The cortical changes consisted in an increase of amplitude, change of configuration and slight decrease of latency, whereas the thalamic responses underwent significaant reductions of latency in addition to change of amplitude and form. Variations in level of vigilance had significant effects on the conditioned evoked cortical responses but little effect on thalamic responses, at least on their initial phases. Thus preferential zones for conditioned changes were defined which may assist in the understanding of the main features of electro-physiological conditioning. © 1969.