Brain Activity and Behavior: EEG and Brain Waves

Action Potential

  • Action potential is a rapid change of voltage across the membrane.
  • Determined by the ratio of positive to negative ions.
  • Depolarization: A quick rise in potential is initiated by the opening of sodium channels.
  • Repolarization: Return to resting potential is mediated by the opening of potassium channels.
  • Balance of ions is maintained by the ATPase, specifically sodium-potassium ATPase, which is energy-dependent.

EEG (Electroencephalogram)

  • EEG measures the activity of large populations of neurons.
  • It requires synchronous activity of many neurons to be picked up through the skull.
  • The signal must pass through the meninges, cerebral spinal fluid, and skull (potentially hair as well).
  • Electrical potential between recording sites is amplified, recorded by a computer, and plotted.
  • EEG represents the sum of all neural activity.

How EEG Works:

  1. Glutamate (excitatory neurotransmitter) is released at active synapses.
  2. Postsynaptic cation channels open, allowing positive ions to enter the postsynaptic cells.
  3. Extracellular fluid becomes more negative.
  4. Positive currents flow down the dendrite, with some leaking back out across the membrane.
  5. Extracellular fluid becomes slightly more positive in these regions.
  6. Electrodes pick up the activity of many thousands of neurons.
  • EEG is generally irregular but can synchronize during specific tasks or across different brain regions.
  • Synchrony is important for learning and memory.
  • Overly synchronized EEG activity may indicate a seizure.

Limitations of EEG

  • EEG can only measure strong, synchronous activity from cortical areas near the skull.
  • Deep brain structures cannot be measured effectively with current EEG techniques.

Brain Wave Patterns and Behavioral States:

  • Different patterns of activity correlate with different behavioral states.

Brain Wave Types:

  • Delta:
    • Lowest Frequency
    • Prominent during sleep and dreaming
  • Theta:
    • During drowsiness and motor activity (e.g., walking)
  • Alpha:
    • During reflective and restful states
    • 8−128-12 Hz
    • Associated with relaxation during wakefulness
  • Beta:
    • During a busy and active mind (e.g., calculations)
    • 13−3013-30 Hz
    • Associated with alertness during wakefulness
    • Also prominent during REM sleep
  • Gamma:
    • During problem-solving and high levels of concentration
    • Associated with eureka moments

Sleep Cycles

  • Non-REM Stage 1: Theta activity (4-8 Hz) intermittently during lighter stages of sleep.
  • Delta: Regular, synchronous activity below 4 Hz, occurs during the deepest stages of slow-wave sleep.
  • Sleep Spindles: Short bursts of higher frequency, lower amplitude activity.
  • K Complex: Single delta wave, a sudden sharp waveform (one per minute), can be triggered by noise.

Detailed Brain Wave Characteristics:

  • Epsilon:
    • Lowest frequency, experienced in very deep and advanced stages of meditation.
  • Delta:
    • Deep sleep and unconsciousness, deep physical relaxation.
  • Theta:
    • Reduced consciousness, deep meditation, high creativity, flashes of insight and inspiration.
  • Alpha:
    • Relaxed focus, good health, important for long-term memory, creativity, and visualization.
  • Beta:
    • Linear, externally directed, left-brain thinking; unsynchronized waves; useful for short-term memory.
  • Gamma:
    • Highest level of consciousness, hyperfocus, crucial for self-awareness and insight; sometimes considered "genius waves."