The EEG during sleep and waking
During the waking state, the EEG is characterized by low voltage, higher frequencies (> 30 Hz). As the person or animal goes into deeper and deeper sleep, slow waves become more prominent. Two particularly prevalent slow waves are delta waves and spindle waves. Delta waves are 0.5 to 4 Hz oscillations that are particularly prominent during deep sleep (stages 3 and 4). Spindle waves are 1-3 second duration epochs of "waxing" and "waning" 6-15 Hz oscillations. The occurrence of both delta waves and spindle waves are indicative of synchronized oscillations in thalamocortical systems.
These changes in the EEG raise several important questions:
- What are the cellular mechanisms for the generation of these different patterns of activity?
- What are the consequences of these different patterns of activity on the processing of sensory information (for example in the visual system)?
- How do the ascending and descending neuromodulatory transmitter systems achieve their control over these patterns of activity?
- How do these different patterns of activity allow the CNS to generate seizures during certain states?