Analysis of various factors involved in EEG synchronization during milk drinking in the cat

Electroencephalographic (EEG) and multineuronal activity (MUA) from several brain structures were recorded in 11 adult cats during milk drinking. Milk drinking elicited parietal and hippocampal EEG synchronization and inhibited multiunit discharge in several brain regions. The proportion of EEG synchronization varied considerably between animals, but remained more or less constant for each cat after several testing days. Neither modification of milk concentration nor fasting influenced the proportions of EEG synchronization during milk drinking. Adaptation of the animals to the experimental environment facilitated the appearance of EEG synchronization during milk drinking. Chlorpromazine (3 mg/kg) significantly increased the proportion of EEG synchronization observed during milk drinking. By contrast, displacement of the head, neck or postural body adjustments during milk drinking blocked EEG synchronization. Amphetamine also had a suppressive effect on the EEG parietal and hippocampal synchronic activity observed during milk drinking. Our results suggest that development of parietal EEG synchronization in response to pleasant stimulation is a complex phenomenon requiring a relaxed condition of the animal, including its adaptation to the experimental environment and relative immobility with the concomitant diminution of afferent inflow from some of the muscles involved in locomotion.