Discuss the EEG patterns characteristic of each sleep stage.

Question

What will be an ideal response?

Answer 1

During waking, EEG recordings typically alternate between beta wave and alpha wave patterns of brain activity. Beta activity is characterized by highly desynchronized, rapid (14-30 cycles per second), irregular, low-amplitude waves. Alpha waves are slightly slower, larger, and more regular than beta waves, with a frequency of 8-13 cycles per second. Sleep consists of alternating periods of rapid eye movement (REM) sleep and non-REM (NREM) sleep. Sleep typically begins when a person enters stage 1 of NREM. In stage 1, the EEG is difficult to distinguish from the waking EEG of a drowsy person. Some theta wave activity now occurs, and heart rate and muscle tension begin to decrease. After 10-15 minutes, stage 1 gives way to stage 2 NREM, which accounts for about 50 percent of the night's entire sleep. The EEG begins to show sleep spindles, short bursts of 12-14 cycle-per-second waves lasting about half a second that are generated by interactions between the thalamus and the cortex. Although spindles are prominent in stage 2, they do occur in other stages of NREM. K-complexes also begin to appear in the stage 2 EEG recording. These waveforms are made up of single delta waves. After about 15 minutes in stage 2, we enter stage 3 and stage 4 NREM sleep. Both stage 3 and stage 4 feature delta wave activity, which is the largest, slowest (1-4 cycles per second), most synchronized waveform of the sleeping state. Stages 3 and 4 differ from each other in that a greater proportion of stage 4 (about half) consists of delta waves. After approximately 90 minutes of NREM, a first period of REM sleep occurs. During REM, the EEG shows activity very similar to beta activity observed during waking, with occasional periods of theta activity as well.