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EEG Basics

Breege LeddyRPSGT

Electro Encephalography (EEG)

Hans Berger, 1924A recording of the electrical activity from the brain using electrodes located on the scalp surface. Each scalp electrode detects the electrocellular activity of about 10 billion cortical neuronsSmeared and distorted by the insulating layers betweencortex and sensor (skin, skull, dura, blood, spinal fluid)

NeuronsNerve cellsGather & transmit electrochemical signals3 Main Parts(1) Cell Body- contains nucleus(2) Axons – long thin projections, carry nerve impulses/action potentials along length of cell(3) Dendrites – Nerve endings. Make connections with other cells & allow neurons to interact with other cells

Neurons create action potential (discrete electrical signals) that travel down the axons & cause release of chemical neurotransmitters at the synpase (an area of near contact between 2 neurons)

Neurotransmitters

Chemicals which relay, amplify & modulate signals between neurons & other cells.Activate a receptor in the dendrite of the neuron that is on the other side of the synapse, the post synaptic neuronThe neurotransmitter, when combined with the receptor, typically causes electrical current with the dendrite/body of the post synaptic neuron.Thousands of post synaptic currents from a single neuron’s dendrites and body sum up to cause the neuron to generate an action potential.EEG reflects the summation of thousands/millions of neurons activity

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EEG WaveformsType Frequency (Hz) Location Normally

Delta Up to 4 Frontally in adultsPosteriorly in children

Adults slow wave sleepIn Babies

Theta 4 - 7 Found in locations not related to task in hand

Young childrenDrowsiness/arousal in older children & adults

Alpha 8 – 12 Posterior regions of brain, both sides. Central sites at rest

RelaxedClosing the eyes

Beta 12 - 30 Both sides, most evident frontally

AlertBusy thinking

International 10 – 20 System

Sleep Physiology

3 Main Parts of Brain :Brain StemCerebellumCerebrum

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Brain structures involved in sleep wake process:

Thalmus Medulla OblongataHypothalmusPonsMidbrainSpinal CordRaphe NucleiBasal ForebrainHippocampusSuprachiasmatic NucleiReticular Formation Neurons

Thalamus

Multiple functions.Relays sensory info from the body to different parts of the brain (cortex)Spindles represent the blocking of info travelling through the neurons between the thalamus & cortex. (N2)As data is blocked, awareness of surroundings is decreased.This blocking is caused by deactivation of the Reticular Activating System (RAS)

Reticular Activating System (RAS)

Consists of group of neurons located in Reticular Formation.Cause wakefulness, alertness, centre of arousal & motivationDeactivation of these neurons leads to decreased alertness, & releases spindles activity in the thalamus (N2)Reticular formation neurons stimulate other neurons through the thalamus → cortex, which develops the cerebral activation the leads to wakefulness

Suprachiasmatic Nucleus

‘Pacemaker’ for circadian rhythmLocated in the hypothalamusProfoundly affected by light.Primary chemicals involved in the circadian rhythm and sleep – wake process include: Dopamine, acethycholine, noradrenaline, histamine and glutamate

Chemical Neurotransmitters

NoradrenalineDopamineAcetylcholineHistamineGlutamate

Dopamine: responsible for movement and responsivenessAcetycholine: at its highest during wake & REMNoradrenaline: maintains & enhances activation of the cerebral cortexHistamine: also activates the cortexGlutamate: includes excitatory amino acid that progress to the cortex, forebrain,& brainstem. Central activation of cortex.

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Recognising Sleep Stage WWakefulnessMuch of the epoch may be obscured by movement.Eye blinksOccipital channels show alpha activity (8 – 13Hz) when eyes closed and or low voltage mixed frequency activity.Amount of alpha is different among patients (age, etc)High EMG tone

Stage N1 (NREM)Consists of relatively low voltage, mixed frequency EEG pattern. Mostly in theta rang (4-7Hz)Disappearance of alpha in central regionsEOG will exhibit slow rolling eye movements as opposed to eye blinksCentral EEG occasionally exhibit vertex sharp waves (sharp waves with high voltage & frequency less than 0.5sec, amplitude as high as 200uV)Chin EMG slightly decreased.Often called transitional stage.Senses are not completely blocked & patients are easily woken & patients may drift in and out of this stage. (sleep stage misperception)Comprises less than 10% of total sleep time in normal healthy adults

Stage N2

Presence of sleep spindlesPresence of K complexes. Comprises approx 50% of the total sleep time in normal healthy adults

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Sleep Spindles

Burst of 11-16 Hz (usually 12 –14 Hz) EEG activityLast at least 0.5 secondsSeen in central regionsStage N2

K ComplexDistinct EEG waveform characterized by aSharp negative deflection followed by a slower positive component.Must be at least 0.5 sec in durationOften occur immediately prior to sleep spindles and are indicative of stage N2Can occur also in stage N3 Can be induced by an arousal

Stage N3 Replaces stage 3 and 4 under the old R & K scoring rules.Delta EEG activity / Slow wave activity (waves at least 75uV in amplitude and are between 0.5 Hz and 2Hz in frequency)Mostly seen in frontal region of brain but also seen in central regionThese slow waves can be seen even in EOG channels but should not be mistaken for eye movements.Seen most often in first third of the night & progressively shorter periods as the night progresses Comprises approx 25% of total sleep time in normal healthy adultsPhysical Restoration and repair of tissues and muscle (Growth hormone emitted0Age dependent.Difficult to wake the patient from N3

Stage R Appearance of relatively low voltage, mixed frequency EEG activity Alpha may/ may not be present but may be little slower than in W.Presence of Rapid Eye Movements (REM)Saw tooth waves may often appear (series of pointed waves in the 2-6Hz range seen in central EEG channel)Muscle atonia (however fast muscle twitches can occur, <0.25 sec )Highly beneficial in restoring the mind, creating long term memory.Typical onset is 90 – 120 minutes after sleep onset.Period are shorter at the beginning of the sleep period & progressively longer as the night progresses.Most stage R occurs in the final third of the night.

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Sawtooth Waves

Other Features: EEG Spikes Characteristics of REM & Non REM SleepREM Sleep Non REM Sleep

EEG Mixed frequencyFast

SpindlesK ComplexesDelta Waves

EMG Absent Present but Low

Eye Movements Rapid Absent

Autonomic Nervous System

Present Absent

Control of Respiration

Altered Same as wake

Respiration during REM Normal Sleep Architecture

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Determinents of SleepHomeostatis (body’s ability to physiologically regulate its inner environment)Circadian RhythmsAge (↑ EEG arousals, ↓ N3 sleep( EEG ↓ in amplitude, ↓ sleep efficiency, ↓ in need for sleep as we get older)Individual Differences (pregnancy, pain)Medications (benzodiazepines, aspirin (supressed N3, ↑N2,)