Plastic Changes of Unit Activity Based on Reinforcing Properties of Extracellular Stimulation of Single Neurons

Abstract

Plasticity was studied in 128 neurons of the non-specific thalamus, reticular formation, hippocampus and neocortex of locally anesthetized curarized rats by reinforcing and indifferent acoustic signal (2000/sec, 0.9 or 3.0 sec duration) with electrical and/or chemical stimuli applied through the recording microelectrode to the investigated cell (10 to 30nA 0.3 or 1.0 sec). In spite of several hundreds of reinforcements stable acoustic reactions could be established only in 17 neurons while transient plastic changes were observed in another 34 units. The incidence of plastic reactions was not significantly different in the examined structures. Positive results were obtained with both excitatory and inhibitory responses used as reinforcement. Another series of experiments was performed in neurons of inferior colliculus displaying marked reactions to sound. In 37 out of 64 units repetitive application of sound stimuli resulted after 12 min. in a significant habituation of the original response; interruption of stimulation for a few minutes evoked dishabituation. Reinforcing the habituated sound stimulus by the polarizing current induced clearcut modification of the acoustic reaction in 14 out of 17 neurons.