Lecture 33 Flashcards
What are inter-ictal spikes?
What are they used for?
In the context of epilepsy, the interictal period is the time between seizures when the individual has recovered from the postictal period (after a seizure)
In epilepsy, interictal periods can involve abnormal brain activity like spikes and sharp waves, which can be used to help diagnose and localize seizure foci
What does EEG slowing look like? What is it?
EEG slowing, in which the dominant alpha rhythm drops to the theta or
delta range is associated with diverse neurological problems including
traumatic brain injury, tumor, stroke
What is amplitude integrated EEG (aEEG) typically used for?
monitoring brain function continuously in
situations like neonatal intensive care units (NICU)
How is epilepsy diagnosed?
EEG monitoring after suspected seizure
Should demonstrate interictal (between seizure) epileptiform activity) and spike and wave patterns
What is the first line of treatment for epilepsy?
Medications which restore inhibitory/excitatory balance
Describe the difference between focal and generalized epilepsy
Focal epilepsy starts in one location/hemisphere, whereas in generalized epilepsy seizures seem to start in multiple locations and/or bilaterally
What are some causes of epilepsy?
- Channelopathies can lead to excess excitation
- Mechanical pressure (such as tumour growth) can cause seizures
- Developmental abnormalities (focal cortical dysplasia - FCD) caused by abnormal neural migration, can cause excess excitation
Local mis-wiring.
Why its so problematic
If you let the epilepsy go, some areas that are not epileptogenic will become epileptogenic at some time (LTP)
Region could become bigger!
Describe the workflow for epilepsy surgery
- Scalp EEG monitoring to look for epileptiform activity (seizures or spikes). Are the seizures focal (i.e. latearlized)?
- Try anti-epileptic medication to restore excitatory/inhibitory balance
- Assess for surgery (only for focal epilepsy)
- Localize epileptogenic region using MRI, neuropsychology, semiology, MEG, fMRI
- MRI: are there brain lesions?
- Neuropsychology: do deficits indicate lesion location?
- Semiology– what does transition to seizure look like clinically? Does the person feel queasy before a seizure manifests clinically? Do they have auras?
Observable signs and symptoms are often correlated with specific brain regions - can help localize seizure onset point - MEG: where do the interictal spikes originate, where is the eloquent cortex ? Most accurate non-invasive mapping.
- fMRI– Where is the eloquent cortex? does the fMRI results concur with the MEG results?
Implant iEEG (intraccranial) to localize epileptogenic cortex and eloquent brain areas. Record for a week to capture multiple seizures. Clinical neurophysiologists look for characteristic waveform patterns like high frequency oscillations (HFOs) (>80Hz) or fast rhythmic discharges. Can also stimulate median nerve and observe electrical responses in brain or stimulate electrodes in brain and observe behaviour (to map out language areas in the brain)
Goal: resect epileptogenic areas while sparing eloquent brain areas
What experiments do they do with MEG and fMRI before epilepsy surgery?
Stimulate median nerve and localize primary motor and somatosensory areas by recording where gamma (>30Hz) responses occur
- This stimulation produces somatosensory evoked fields (SEFs) and can also induce gamma-band (>30 Hz) activity related to sensorimotor processing
- The first response (often referred to as Peak 1) typically localizes to the primary somatosensory cortex (S1) — specifically, the hand area, which lies in the postcentral gyrus, contralateral to the stimulated hand
- A later response (sometimes called Peak 2) may correspond to activity in the primary motor cortex (M1), also contralateral to the stimulated side.
Verb generation paradigm: subjects see pictures of items and think of verbs associated with them. Investigate brain region involved in language processing and spare these areas so person can still speak and comprehend language
- mapping brocas area
Describe the anatomical patterns of activation/deactivation found on fMRI in individuals with petit mal seizures (absence seizures)
Petit mal: generalized epilepsy, characterized by periods of
staring, inattentiveness, and interruption of consciousness
fMRI reveals anatomical pattern of activation/deactivation during absence seizure
1) Ictal activation spreading to encompass ’cortical consciousness network’
2) Activation spreads to thalamus
3) Deactivation in the ‘cortical consciousness network’
Describe the anatomical patterns of activation/deactivation found on fMRI in individuals with Tonic-clonic (grand mal) seizures)
- Tonic-clonic (grand mal) seizures
typically involve a ‘tonic’ phase
characterized by rigidity and a ‘clonic’
phase characterized by convulsions - Involves loss of consciousness
- Studies of fMRI connectivity during
tonic-clonic seizures reveal
1) Decreased connectivity involving
prefrontal, cingulate, and parietal
areas
2) Increased connectivity between
thalamus and cerebellum
Describe the resting-state fMRI study
Resting-state fMRI is recorded in healthy controls and patients with disorders of consciousness (e.g., coma, vegetative state, minimally conscious state).
Researchers analyzed functional connectivity between brain regions during rest (i.e., without task performance).
Connectivity within the DMN (e.g., between the medial prefrontal cortex, lateral posterior parietal cortex) varies with level of consciousness:
Higher DMN connectivity is typically associated with greater awareness.
Reduced or disrupted DMN connectivity is observed in patients with lower levels of consciousness.
Explain the functional anatomy of a coma
Results in reduced excitation within thalamocortical system
Can result from:
- loss of excitatory input from cholinergic brainstem nuclei which normally help activate the thalamus and cortex
- Abnormal inhibitory signaling from the basal ganglia can disrupt thalamic output, further suppressing cortical activation. Example: excessive inhibitory output from the GPi
