Excitability Changes of Facial Motoneurons of Cats Related to Conditioned and Unconditioned Facial Motor Responses
The electrical excitability of facial motoneurons changes after Pavlovian conditioning (“Conditioned” group) and after repetitive presentation of USs such as glabella tap (“US-only” group). Measurements were made in awake, unparalyzed cats using intracellular recording and stimulation techniques. Threshold currents required to elicit action potentials were significantly lower in “Conditioned” and “US-only” groups than in a “Naive” control group. A decrease in the threshold of depolarizing current required to produce spike discharges was correlated with an increase in input resistance. The increase in excitability to intracellularly injected current persisted for more than four weeks in cells of the “Conditioned” group, but decayed in cells recorded from the “US-only” group. The transient increase in excitability after presentation of USs coincided with behavioral facilitation of subsequently acquired Pavlovian eyeblink conditioning. This facilitation of learned motor performance produced by prior, repeated presentations of USs may be analogous to the phenomena of reflex dominance and latent facilitation.
KeywordsInput Resistance Pavlovian Conditioning Threshold Current Facial Nucleus Electrical Excitability
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