Activities of single neurons in midbrain and thalamus of cats during conditioned nocifensive behavior.
Extracellular recordings of neuronal activity were performed in 3 conscious cats in the rostral mesencephalic reticular formation (MRF) and in the nucleus posterior (PO) of the thalamus. The animals were trained by operant conditioning to operate a panel switch with a forepaw to escape a noxious cutaneous heat stimulus. We recorded 12 neurons in the MRF, which responded in association with this nocifensive behavior. Some of the neurons increased their firing rate before the noxious stimulus was terminated, whereas other neurons responded immediately afterwards. The activity of these neurons, however, could be related to the animal's behavior, which was independent of the noxious stimuli. It was found that the neurons showed changes in firing patterns when the animal reacted to a discriminative light stimulus in order to obtain a milk reward. In the PO of the thalamus we did not find any neurons, which could be activated by noxious heating or any nocifensive-related behavior. Modification of the discharge patterns, however, occurred in relation to sensory events and behavioral acts.
D000818:Animals; D002415:Cats; D003216:Conditioning, Operant / Q000502:physiology; D004594:Electrophysiology; D008636:Mesencephalon / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D010775:Photic Stimulation; D013788:Thalamus / Q000502:physiology*