Gamma rhythms occur in humans and other mammals following sensory stimuli. They often occur in brief runs in these responses. "Induced rhythms" at 50-60 Hz were first described in olfactory bulb by Adrian [1]. They have since been found in: olfactory [4], visual [3a,3b,6-8,11,22], auditory [13,16], somatosensory [2] and motor cortex [17,19,21]. "EEG data recorded from 22 frequent gamblers while theyplayed a laboratory, video-gambling game. On each hand,four "cards" were presented sequentially in the center of avideo screen using an interstimulus interval of 2600 ms anda stimulus duration of 330 ms in counterbalanced wager andnonwager blocks. Then, subjects guessed which card wouldlater be selected as the target by a computerized, randomprocess. Guessing accuracy was at chance level, p = .465,one-tailed binomial. EEG analyses focussed on 40 Hz powerin the 150-500 msec latency window following delivery ofthe target and nontarget cards. ANOVAs indicated greater40 Hz power for targets than for nontargets over left-frontal scalp in both wager and nonwager conditions,F (1/21) = 7.87, p = .005, and over the right-posteriorscalp in the wager condition, F (1/21) = 5.81, p = .013,both one-tailed.These findings indicate that1) 40 Hz activity is involved in the processing of psiinformation.2) the attentional mechanisms of the brain utilized infocused arousal are also utilized in processing psiinformation in the wager condition, although theleft-frontal effect, found in both wager and nonwagerconditions, is unlike the posterior-parietal locus of40 Hz effects observed by Sheer. Neither the leftfrontal nor the right parietal loci of effects overlayprimary sensory areas of the cerebral cortex,suggesting that the 40 Hz effects we observed werenot due to sensory processes.The present EEG findings are consistent with the notion ofunconscious or preconscious psi. Guessing accuracy was atchance level and yet 40 Hz activity following target andnontarget stimuli differed significantly. Thus, althoughconscious behavior was not influenced by psi information,the differential brain responses indicated recognition atsome level that the stimuli belonged to differentcategories. These findings in the frequency domain supportand extend our previous findings with event-related brainpotentials."