THALAMO-CORTICAL WAXING AND WANING NATURE AND ACTIVITIES OF CORTICAL NEURONS IN THE RABBIT

Abstract

1. Interrelations between the slow potential sequence and neuron activities in the sensorimotor cortex to the stimulations of thalamic relay (VPL) and nonspecific (VA) nuclei were studied in the rabbit and the results led to the following considerations.
2. The initial positive deflection recorded at the cortical surface is the reflection of the intracortical negative potential which resulted from massive terminal activities in the fastest thalamo-cortical projection fibers and synaptic activities in some cortical neurons firing with short latency and adapting in a short time.
3. The augmenting positive-negative potential is brought about by the deep negative-positive field potential which results from EPSPs and IPSPs generated in many cortical cells and reflects upon the cortex in the reverse sign. In addition, postsynaptic activities in upper layers must participate in the formation of this potential, especially of the negative phase.
4. Gradual synchronization of PSPs produced in respective neuron makes the intracortical field potential larger when stimulated at 8 c/s. While IPSPs developing later, probably owing to the activities of inhibitory interneurons, lower the height of EPSPs and lead to the inhibition or cessation of firings. These are possible mechanisms by which the waxing and waning occur in response to low-frequency VPL stimulation.
5. Less evidence was obtained to allow making the distinct relation between neuron activities and cortical slow potentials to 8 c/s VA stimulation. Therefore, strict ideas on the origins of component potentials in the recruiting response were not obtained. It is reasonable, however, to presume that the same elements and mechanisms as in the augmenting resjcrse alEo take a part in the recruiting response.