Electroencephalogram (EEG) : recording of electrical activity from cortical neurons of the brain

• Correlation between activity level or level of input and synchronization of cortical neurons

  • Neurons will depolarize as long as individual is alive, regardless of activity or input level

  • Activity or input level determines depolarization pattern

    • Increased input → decreased synchronization → increased frequency

      • Neurons respond and depolarize as sensory input arrives

    • Decreased input → increased synchronization → decreased frequency

      • Neurons synchronize and depolarize together

• Named wave patterns defined by range of frequency and amplitude

  • Overall wave pattern named for wave type that dominates

  • Amplitude and frequency inversely related

  • Beta: 14-30 Hz, 5-10 μV, active, alert, and focused

  • Alpha: 8-13 Hz, 8-14 μV, awake but drowsey, not active/not focused, daydreaming

  • Theta: 4-7 Hz, 100 μV, light sleep

  • Delta: 0.5-3 Hz, 20-200 μV, deep sleep, unconscious

    

Sleep

• Awake

  • Transition from Beta to alpha waves (due to cutting off visual input - eyes closed)

• Four numbered stages (or three numbered stages depending on source) of slow wave or non-REM (NREM) sleep

  • Sleep stage 1 (SWS1 or NREM1) – brief transition between awake state and sleep state, transition from alpha to theta waves

    • Slow eye movement and floating sensation

  • Sleep stage 2 (SWS2 or NREM2) – Light sleep with theta dominant wave pattern

    • Sleep spindles only occur in stage 2 as response to stimulus → stay asleep/not wake up (higher average of sleep spindle = better sleep)

    • Slight decrease in breathing and heart rate

    • Eyes generally still

  • Stage 3 and 4 (SWS3 and 4 or NREM3 and 4) - deep sleep, delta wave dominant pattern

    • Oblivious sleep

    • Decrease in body temp, breathing, and heart rates

    • Unconscious shifts in position

    • Sleepwalking

  • REM (rapid eye movement) - high frequency beta-like wave pattern

    • Called paradoxical sleep due to the high frequency pattern

    • Atonia - paralysis of voluntary muscles (sleep paralysis), only extraocular muscles and diaphragm remain active

    • Most vivid dreams

• Cycle through stages

  • Early cycles include deep sleep

  • Later cycles only stage 2 and REM

  • Cycles “shortcut” as time progress