Background Gamma Activity in the Electroencephalogram as a Measure of the Level of Sustained (tonic) Attention during Execution of the “Active Oddball” Paradigm in Rabbits

works in supporting the body’s appropriate responses to sensory stimuli has been demonstrated and analyzed in detail by recording spike activity from single neurons and low-frequency EEG activity in the range 4–10 Hz [3] during the formation and execution of conditioned reflex tasks of different levels of difficulty. Current physiological studies of brain activation, as well as attention and perception, made wide use of recording of the high-frequency component of the EEG spectrum – the gamma rhythm, i.e., oscillations of cortical potentials in the range 30–70 Hz and above [1, 2, 6, 14, 16, 18, 21]. Tonic gamma activity is known to change in accordance with the ongoing state of the subject and the task being executed. In particular, generation of gamma activity increases in the state of attention and/or mental loading. Thus, studies in 1980 showed that increases in the EEG gamma rhythm in cats occurred at the time point at which they paid full attention to their target prey [12]. Similarly, gamma rhythm power in humans increased during cognitive loading as compared with the resting state; gamma activity differed in this way from activity in the beta range – which, conversely, decreased when cognitive loading increased [20]. Existing data indicate that the level of background, i.e., spontaneous, gamma activity and the subject’s response to sensory stimuli are related to each other. For example, psychophysical experiments have shown that correct responses to target stimuli are preceded by a higher background gamma level than missed responses to these stimuli [22]. Expectation of a stimulus and preparation to execute a reaction in response to a stimulus also lead to increases in gamma activity [2, 18]. On the other hand, episodes of significant increases and synchronization of the gamma rhythm to above the baseline level are accompanied by the so-called inattention blindness, in which responses to sensory stimuli are blocked [15]. Neuroscience and Behavioral Physiology, Vol. 42, No. 6, July, 2012