In a healthy alert adult sitting with eyes closed, which of the following EEG rhythms will be seen when electrode is placed in occipital region?
Ans. c. (Alpha waves ) (Ref. Guyton physiology 11th ed., 742)NORMAL SLEEPStage of sleepCharacteristic features1. Stage 1 (5%)EEG: The appearance of theta waves (slow 3 to 7 cycles per second)Disappearance of alpha waves - drowsy (rapid 8 to 12 cycles per second)2. Stage 2 (45%)Longest stageEEG: K complexes & sleep spindles (very rapid 12 to 14 cycles per second)3. Stage 3 (12.5%)EEG: appearance of delta waves (slowest < 2 cycles per second).Hardest to arouseTends to vanish in the elderlyStage 3 with stage 4 are called slow wave sleep or delta sleep4. Stage 4 (12.5%)EEG: continuation of delta wave5. REM sleep (25%)EEG: Saw-tooth wavesREM like SEX: Pulse & Penile/Clitoral arousal, but |with ageLengthens in time as the night progressesIncreased during the second half of the nightFour simple periodic rhythms recorded in the EEG are alpha, beta, delta, and theta. The four basic rhythms have been associated with various states.RhythmFreq (Hz)Amp (mV)alpha8-1320-200beta13-305-10delta1-520-200theta4-810Alpha: In general, the alpha rhythm is the prominent EEG wave pattern of an adult who is awake but relaxed with eyes closed. Each region of the brain had a characteristic alpha rhythm but alpha waves of the greatest amplitude are recorded from the occipital and parietal regions of the cerebral cortex. In general, amplitudes of alpha waves diminish when subjects open their eyes and are attentive to external stimuli although some subjects trained in relaxation techniques can maintain high alpha amplitudes even with their eyes open.Beta: Beta rhythms occur in individuals who are alert and attentive to external stimuli or exert specific mental effort, or paradoxically, beta rhythms also occur during deep sleep, REM sleep when the eyes switch back and forth. This does not mean that there is less electrical activity, rather that the "positive" and "negative" activities are starting to counterbalance so that the sum of the electrical activity is less. Thus, instead of getting the wave-like synchronized pattern of alpha waves, desynchronization or alpha block occurs. So, the beta wave represents arousal of the cortex to a higher state of alertness or tension. It may also be associated with "remembering" or retrieving memories.Delta and Theta: Delta and theta rhythms are low-frequency EEG patterns that increase during sleep in the normal adult. As people move from lighter to deeper stages of sleep (prior to REM sleep), the occurrence of alpha waves diminish and is gradually replaced by the lower frequency theta and then delta frequency rhythms.Additional Educational Points:NEUROTRANSMITTERS OF SLEEP (T SA-ND4)Serotonin# | during sleep -Initiates sleepAcetylcholine# | during sleep -| REM sleepNorepinephrine# | during sleep -|REM sleepDopamine# | during sleep - | arousal & wakefulnessCHEMICAL EFFECTS ON SLEEP# Tryptophan# | Serotonin; | total sleep time# Dopamine agonists (Bromocriptine)# Produces arousal; | total sleep time# Dopamine antagonists (Haloperidol)# | Arousal; Produce sleep# Imipramine# | Stage 4 & used for Rx of Enuresis# Benzodiazepines# | Stage 4 & used for Rx of Night Terrors & Sleepwalking# Benzodiazepines withdrawal after chronic use# T sleep latency (Can't Sleep)# Alcohol & Barbiturate intoxication# | REM# Alcohol & Barbiturate withdrawal# | REMParasomniasParasomniasSleeping StageCharacteristicsRxNightmare(Bad Dream)Occurs during REM sleepMemory of events depends upon awakening.| during stress.Reported by 50% of the population.REM suppressants such as TricyclicAnti-depressant's (TCAs)Night TerrorOccurs during stages 3 & 4Awakened by scream or intense anxietyNo memory of the event.> in children (Boys)No treatment is necessary OR use drugs to suppress stages 3 & A, such as BenzodiazepinesSleeptalkingCan occur in all stages of sleepUsually involves a few words.May accompany night terrors & sleepwalking. > in children.No treatment is necessary.SleepwalkingOccurs during stages 3 & 4Sequence of behaviors without full consciousness. No memory of the events. Begins at young age > in boysUse drugs to suppress stages 3 & 4, such as Benzodiazepines.
Delta (0.5-4 Hz)
Theta (4-7 Hz)
Alpha (8-13 Hz)
Fast irregular low-voltage activity
Nervous System