Neuronal activity within the nucleus basalis and conditioned neocortical electroencephalographic activation.

The relationship between neuronal activity within the nucleus basalis (NB) and conditioned neocortical EEG activation was investigated in New Zealand rabbits during Pavlovian differential conditioning. Twenty-seven of 56 neurons recorded in conditioned animals demonstrated a significantly greater change in activity to a tone (CS+) that predicted the occurrence of a mildly aversive unconditioned stimulus when compared to a tone (CS-) that did not. Twenty-four of these 27 neurons demonstrated a significant increase in activity to the CS+ compared to the CS-, while the remaining three neurons demonstrated a significant decrease in activity to the CS+ compared to the CS-. In 24 of these 27 neurons (89%) these changes in neuronal activity during CS presentations correlated significantly with a decrease in the power of delta activity in the EEG. In addition, 13 of these 24 neurons (54%) demonstrated significant correlations between neuronal activity and the power of delta activity during CS-free periods. In experimentally naive animals, the activity of 10 of 22 neurons (45%) recorded within the region of the NB correlated with the power of delta activity in the EEG during stimulus-free periods. These results complement a growing body of evidence and provide strong support for the hypothesis that the NB contributes to neocortical activation in the conscious animal.