Enhanced frontal cortex activation in rats by convergent amygdaloid and noxious sensory signals

The modulation of frontal cortical EEG activation to noxious somatosensory (tail pressure) and olfactory (acetone) stimulation by the basal amygdala was examined in urethane-anesthetized rats. Mild tail pressure produced no EEG activation, while acetone (sniffed by freely breathing rats or drawn across the olfactory epithelium in tracheotomized rats) produced a moderate suppression of large-amplitude synchronized EEG patterns. Concurrent, low-intensity 100 Hz stimulation of the basal amygdala permitted EEG activation to tail pressure to occur, and strongly enhanced olfactory-induced cortical activation. These results indicate that excitation of the basal amygdala potentiates frontal cortical responsiveness to aversive sensory events. This may provide a mechanism to facilitate cortical excitability and processing by amygdaloid neuronal activity.