Lecture 17: Cortical Electrical Recordings Flashcards
What is idiopathic epilepsy
Seizures as a result of an unknown cause
What is primary epilepsy
Genetic
What is symptomatic epilepsy
Known, underlying cause: developmental, degenerative, inflammatory, infectious, neoplastic, and traumatic
What is reactive epilepsy
Metabolic, nutritional or toxic cause
What is reflex epilepsy
Sensory stimuli triggers an episode
What is a seizure
Physical findings and/or changes in behavior that result from abnormal electrical activity in the brain. May include motor, sensory, autonomic or psychic effects
What is epilepsy
Abnormal activity in the cerebral cortex that results in a seizure. A epileptic seizure is a clinical sign of an abnormal forebrain disorder
What is status epilepticus
A seizure that lasts for 5 minutes or longer or multiple seizures within a 5 minute period
What are cluster seizures
Increased frequency of seizures within a few days or 2 seizures within 24 hours
What are the three phases of a seizure
- Pro-dromal
- Citrus
- Post-ictal
What is the prodromal phase
Pre-octal period, abnormal behavior that may occur hours before ictus
What is ictus
Seizure lasting 1-2 minutes, characterized by the loss of consciousness and alteration of muscle tone, repetitive movements
What is “aura”
Onset of ictus
What is the post-octal period
Return to normal or altered behavior, recovery period
What do EEG’s measure
Collective electrical activity neurons in the cortex
What layer of the cortex is made of glia cells and dendrites of neurons in lower layers
Layer 1
What layers of the cortex contain Stellate cells that receive afferents from brainstem; pyramidal cells send axons to other parts of the cortex
Layers 2-6
What layer receives thalamic inputs
Layer 4
What layer is the motor efferent neurons to the spinal cord
Layer 5
What layer of the cortex has projections to basal ganglia and thalamus
Layer 6
What are the major cell types in the cortex
- Pyramidal neurons- Long distance excitatory
- Stellate neurons- local excitatory and inhibitory
- Glial cells
What are focal seizures
Partial, originates in a localized portion of the cortex=seizure focus
What is a generalized seizure
Involves both hemispheres of the brain, originates in the thalamus with abnormal activity in thalamocortical circuit
What is a secondary generalized seizure
When a focal seizure starts locally and spread to the rest of the cortex, creating a generalized seizure
What what two ion channels are responsible for inhibitory or excitatory activity
- Voltage gated channels
- Ligand gated channels
GABA binding Cl- causes ___
Hyperpolarization
Glutamate binding AMPA and NMDA causes
Depolarization
What is the resting state of Na+ channels
Channel is closed
What is the active state of Na+ channels
Channel is briefly open
What is the inactive state of Na+ channels
Channel is closed again and not sensitive to membrane depolarization
Describe a normal action potential
- Na+ channels open causing depolarization
- Ca2+ open if present
- Potassium channels open causing them to repolarize
What is epilepsy channelopathies
Mutations to these channels results in enhanced excitatbility or loss of inhibition
___depolarization is a characteristic of a seizure
Paroxysmal
What is a paroxysmal depolarization shift
Sudden, large (50-200mV), long (50-200msec) depolarization
Triggers a train of action potentials
What is the depolarization phase of the PDS
Ca2+ and glutamate channel activation
Initial depolarization mediated by AMPA receptors, sustained by NMDA
What receptors cause the initial depolarization during the PDS
AMPA
What receptors cause the sustained depolarization in PDS
NMDA
What is the hyperpolarization phase during the PDS
Termination of the PDS the cell hyperpolarizes because Cl- and K+ flux via GAVA receptors, causing a prolonged period of hyerpolarization
When do PDSs remain localized
In a healthy nervous system where there are less than 1000 neurons involved
What happens when there are more than 1000 neurons involved in PDSs
Activity spreads across the cortex, recurrent axons of affected cells activity inhibitory interneurons, increased inhibition dampens spread of seizure to neighboring cells
___inhibition contains seizure focus by limiting PDSs
Surround
When surround inhibition breaks down the ___spreads
Seizure
Seizure spread can occur in what 2 scenarios
- Neurons die- loss of inhibitory neurons may occur because of head injury, clot or scarring tumor
- Channelopathies- disorders in ion channels, causing increase Na+ and Ca2+ and decrease K+
What ions increase when a a seizure occurs due to channelopathies
Na+ and Ca2+
What ions decrease when a seizure occurs due to channelopathies
K+
what is indicated by #1
Paroxysmal depolarization shift
A positive voltage change will cause a ___deflection in the EEG
Downward
A negative voltage change will cause an ___deflection in the EEG
Upward
When are EEG’s useful
- Identifying and classifying epilepsies
- Localizing lesions in the cortex
- Sleep studies
- Legal determination of brain death
What do the alpha waves show in an awake EEG
Regular, high amplitude, sweeping pattern
What do beta waves show in an awake EEG
Irregular and have lower amplitude
Are alpha or beta waves activated when eyes are closed
Alpha
Are alpha or beta waves activated when eyes are open
Beta
What waves are indicated by 1-3
- Alpha
- Beta
- Alpha
What do delta waves characterize in a sleeping EEG
Characterize slow wave sleep
What does paradoxical sleep (aka REM) look like during sleeping EEG
Characterized by low amplitude, irregular EEG
What waves are indicated by 1-2
- Delta
- REM
___are bursts of activity from the thalamus to the cortex
Sleep spindles
___ are extensive activities in the primary sensory cortices
K complexes
Identify the waves 1-7
- Awake- beta waves
- Drowsy, relaxed- alpha waves
- Stage 1 sleep- theta waves
- Sleep spindle
- K complex
- Stage 3/4 sleep- delta activity
- REM sleep
Is the following EEG representative of a partial or generalized seizure
Partial seizure
Is the following EEG indicative of a partial or generalized seizure
Generalized seizure
How do flashing lights induce seizures
Photosensitive epilepsy brain responds to excessively to certain visual stimuli, triggering seizures.
Flashes of light at 20Hz are most likely to induce seizures
