The genetics of oscillations in the human brain.

Recording brain electrical activity using scalp electrodes provides a noninvasive, sensitive measure of brain function in humans. These neuroelectric phenomena may be recorded during the continuous electroencephalogram (EEG) when the subject is at rest, and not involved in a task, or one may record the time-specific event-related brain potentials (ERPs) during specific cognitive tasks. These techniques yield spatiotemporal activity maps (i.e. brain activity as it occurs in both space and time). The EEG consists of the activity of an ensemble of generators producing rhythmic activity in several frequency ranges. In the purely resting state, these oscillations are seemingly random; however, with the application of sensory stimulation, they become coupled and act together coherently. This synchronization and enhancement of EEG activity gives rise to an " evoked " (phase-locked) or " induced " (non-phase locked) rhythmicity. This rhythmicity may also occur without defined physical stimulation, but may be triggered by cognitive operations. The superimposition of these multiple event-related oscillations (EROs) of different frequencies underlies the ERP, and represents multiple sensory and cognitive functions. Basic dynamics in the brain are governed by the brain's natural oscillations, namely: delta (1.0– 3.0 Hz), theta (3.5–7.5 Hz), alpha (8.0–11.5 Hz), beta (12.0–28.0 Hz), and gamma (28.5–50.0 Hz). It is becoming increasingly obvious that these oscillations provide basic links to brain functions, especially for communication and associative functions , and that multiple oscillatory responses provide integrative brain functions. Complex functions are, as a rule manifested by several superimposed oscillations with various degrees of amplitude, durations, and delays. EROs are considered to be different from the ongoing " idling rhythms " , since a process-related " partial-phase resetting " occurs in different EEG frequency bands in response to sensory or cognitive stimulation (e.g. Basar, 1980; Makeig et al., 2002). Evidence suggests that ERP features arise from oscillatory changes due to sensory or cognitive processes which influence the dynamics of ongoing EEG rhythms of different It should be noted that various cognitive processes have been attributed to different frequency rhythms