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Flashcards in EEG and Sleep Deck (48)
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What is EEG?


  • recording of the rhythmic activity of the brain
  • made from the cerebral cortex
  • electrodes placed on the skull


Richard Caton

  • first person to probe the brain of animals with electrodes
  • Discovered electrical brain signals
  • used a reflecting galvanometer
    • measure micro-amperes
    • primitive form of amplification


Hans Berger

  • First to record EEG from humans
  • defined all major EEG rhythms 


Basic EEG Frequencies:

  • Alpha Rhythm 
    • 8-13 Hz
    • awake, relaxed adults
    • closed eyes
  • Beta Rhythm
    • 13-30 Hz
      • higher frequencies
    • awake adults
    • open eyes
  • Theta Rhythm
    • 4-7 Hz
      • slower higher amplitude
    • drowsiness
  • Delta Rhythm
    • 0.5-4Hz
      • very slow, high amplitude
    • Sleep


Mechanism of EEG

  • All the action potentials on the neuronal cell bodies
  • EEGs are derived from alternating excitatory or inhibitory synaptic potentials
  • in cortical neurons as a result of thalamocortical inputs (and other inputs)


What is the principle source of EEG electrical activity?

  • Pyramidal cells
    • projects from the thalamus to the contralateral cortex
    • sum of all excitatory or inhibitory synaptic potentials


EEG as a diagnostic tool:

  • Coma-EEG
    • Mainly Delta Activity 
  • Brain Dead:
    • sustained flat EEG reading
  • Epilepsy: (petit mal)
  • Epilepsy (grand mal)
  • Partial Seizures
    • spikes in affected areas


EEG: Test the integrity of sensory pathway

  • SEP
    • somatosensory evoked potentials 
    • cortical potentials generated by the response of sensory neurons to the stimluation of peripheral nerves
    • ex: stimulate skin on hand
    • If no conductance= peripheral nerve has been severed/damaged


Types of EEG: Comatose patient

  • centralized slow waves
  • mainly delta activity


Type of EEG: Epilepsy different types

  • Generalized seizures:
    • Grand Mal:
    • Petit Mal
  • Partial Seizures (aka focal seizures)
    • Temporal lobe seizure
    • Focal seizure
    • Secondary Generalized Seizures


Seizure: Definition

  • Latin-to take possesion of
  • the clinical manifestation of abnormal, excessive, hypersynchronous discharge of a population of cortical neurons



  • Chronic disorder of CNS
  • recurrent unprovoked seizures


Seizure initiation is characterized by:

2 concurrent events:

  • high frequency bursts of action potentials
  • hypersynchronization of neuronal population


Pathway for seizure propagation

  • Seizures may start in certain regions then spread


Petit Mal attack (seizure)

  • EEG
    • Symmetrical
    • highly synchronized activity
  • aka Absence seizure
  • Milder type of activity
  • causes unconsciousness with no convulsions
    • begins and ends abruptly and without warning
    • blank stare
    • No confusion
    • can Resume activity immediatelly
  • After there is no memory of the seizure


Grand Mal attack (seizure)

  • AKA Generalized tonic-clonic seizure
  • usually short cry and fall to the ground
  • Tonic phase
    • muscles will stiffen
  • Clonic phase
    • extremities will jerk and twitch 
  • Bladder control may be lost
  • Loss of consciousness and regained slowly
  • Wide distribution of seizure activity to both hemispheres 



Similarity between Grand Mal and Petit Mal

  • Consciousness is slowest
  • no recollection of the seizure 
  • Memory is often lost just in recent events just before the seizure along with the seizure


Focal Cortical Seizures

  • AKA Simple partial seizures
  • Result from epileptic activity
  • localized in one hemisphere 
    • usually cortex or limbic system
  • Consciousness is not impaired
  • May have abnormal muscle contraction
    • ex: abnormal head movement
  • can usually talk and answer questions 


Temporal Lobe seizure

  • starts in  the temporal lobe
  • Involves sensory changes
    • Ex: smelling an unusual odor 
  • Most common cause is:
    • mesial temporal sclerosis
    • hippocampal sclerosis 
  • Risk factors
    • Aging
    • Stroke
    • Vascular 


Mechanism of Seizure initiation

  • Poorly understood 
  • initially- local changes in permeability for potassium and calcium ions
    • Increase in extracellular K+ brings membrane closer to threshold
  • Accumulation of Ca2+ in presynaptic terminals, leading to enhanced neurotransmitter release (depolarization)
  • So the depolarization-induced activation of the NMDA subtype of the excitatory amino acid receptor (glutamate)
    • opens more Ca2+ channels-->Ca2+ influx
    • Neuronal activation (from further depolarization due to influx)


Seizures: Sensory Stimulations

  • May be induced by strong sensory experiences
  • Audiogenic seizures
    • high frequency of sound=Sensory
  • Visual Seizures



  • Normal, easily reversible, recurrent, and spontaneous state of decreased and less efficient responsiveness to external stimuli 
  • Eyes closed
  • consciousness completely or partial lost
  • In humans and other mammals the brain undergoes a cycle of brain-wave activity that includes intervals of dreaming. 


Moruzzi and Magoun: late 1940s

2 observations:

  • transection of ascending sensory pathway in the brainstem did not interfere with wakefullness
  • Lesion of RF produced stupor with EEG pattern resembled sleep


  • tonic activity of RF keeps brain awake


Moruzzi & Colleague: Late 1950s

  • Transection of the brainstem including RF through the pons
    • greatly reduced sleep 
  • Rostral portion of RF 
    • above pons
    • contains neurons whose activity-wakefullness
    • Activity was inhibited by neurons in the RF below the pons


What are the different areas of the brain that can put someon to sleep or awake if stimulated?

  • Awake
    • Rostral Reticular formation
      • Ascending reticular activating system
  • Sleep:
    • Thalamic nuclei
      • intralaminar nucleus
    • Caudal  RF
    • Hypothalamus



Ascending Reticualr Activating System

  • aka extra thalamic control modulators system
  • set of connected nuclei in the brain of vertebrae 
  • Regulate:
    • Wakefulness
    • sleep-wake transitions 
  • Part of the RF
  • Projects to various nuclei in the thalamus and other Brian nuclei associated with NTs
  • Awake
    • RF
      • Rostral part=ARAS
      • project to limbic system and cortex 
  • sleep
    • RF
      • caudal part
    • Hypothalamus
    • Thalmic nuclei


Brain Nuclei that contribute to sleep-wake

  • Sleep:
    • Raphe nuclei
      • serotoninergic 
      • brainstem
    • Cholinergic nucleus
      • brainstem
  • Wake
    • Locus Coeruleus
      • brainstem
      • noradrenergic 
    • Tuberomammillary nucleus of hypothalamus
      • Hypothalamus


Hypothalamic Nuclei: involved in regulation of sleep-wake cycle

  • Suprachiasmatic Nucleus 
    • control circadian rhythm 
    • central pacemaker of circadian timing 
      • receives direct input from the retina
      • sends oscillations to other areas of the brain ==>"Slave oscillators) in pineal gland 
    • bilateral structure
    • anterior part of hypothalamus
  • Tuberomammillary nucleus
    • histminergic nucleus
    • located in posterior third of hypothalamus
    • consists largely of histaminergic neurons
    • involved in:
      • arousal
      • learning
      • memory
      • sleep 
      • energy balance
  • VLPO (Ventrolateral preoptic nucleus)
    • Active during non-REM sleep
    • released inhibitory NTs
      • GABA
      • galanin 


Regulation of Sleep-wake Cycle 

  • Balance between hypothalamus nuclei and brainstem nuclei 
  • Hypothalamus Nuclei
    • VLPO (Ventrolateral preoptic area)
      • Inhibits Tuberomammillary Nucleus
        • GABA
        • galanin 
      • Brainstem Nuclei
        • Cholinergic nuclei
        • Locus Coeruleus 
        • Raphe Nuclei 
    • Orexin Nucleus
      • Hypothalamic neurons produce Orexin
        • Stimulates:
          • Tuberomammillary nucleus
          • cerebral cortex and basal forebrain
          • Raphe nucleus in brainstem
            • keep Brain awake 


Suprachiasmatic Nuclei

Suprachiasmatic Nucleus 

  • control circadian rhythm 
  • central pacemaker of circadian timing 
    • receives direct input from the retina 
    • sends oscillations to other areas of the brain ==>"Slave oscillators) in pineal gland 
  • bilateral structure
  • anterior part of hypothalamus
  • Pathway:
    • Light hits the retina and stimulates photosensitive receptor ganglion cells
      • not rods and cones
    • send info to suprachiasmatic nucleus(hypothalamus)--> brainstem--> spinal cord--> intermedia lateral column--> enters Peripheral nervous system-->Superior Cervical Ganglion --> pineal gland