40 HZ EEG and focused arousal behavior in the cat

The relationship between 40 HZ EEG and focused arousal behavior has been investigated in 6 cats. Indwelling chronic electrodes were implanted in the nucleus parabrachialis (PB) of the rostral pons, lateral geniculate nucleus (LGN) of the thalamus, and visual cortex (VC). After recovery, EEG and behavior were recorded across the following experimental phases: 1) baseline, 2) presentation of a novel 7 cps visual stimulus and habituation to this stimulus, and 3) UCS - CS pairing of this visual stimulus with a mildly aversive event and adaptation to the pairing. An increase in the frequency of 40 HZ peaks was observed in the initial stages of phase 2 and phase 3 in comparison to phase 1. 40 HZ activity in the LGN and VC was strongly correlated with 40 HZ activity in PB. These results replicate previous findings that a high frequency low amplitude EEG signal is highly correlated with focused arousal, attention, and the acquisition phase of learning. Furthermore, results suggest that PB functions, through excitatory post synaptic potential (EPSP) biasing, to increase the probability of firing of fast frequency EEG between the LGN and VC during UCS-CS pairing of a visual stimulus. Ascending cholinergic input from PB is a critical neural substrate for focused arousal. Applications to learning and cognitive dysfunction are discussed.