Lecture 33 Flashcards
(36 cards)
1
Q
When would we record inter-ictal spikes?
A
- it is recorded in epileptic patients when they are not having seizures
- ‘between’ seizures
2
Q
What do inter-ical spikes help us determine?
A
- they are silent indicators that brain is prone to seizures even if one isn’t having one in the moment
- they help us diagnose epilepsy and lateralize (which side) the side the seizures coming from
3
Q
How do seizures manifest?
A
- excessive synchronized activity relating to to much excitation
4
Q
What is focal slowing on an EEG?
A
- focal slowing refers indicates that dominant alpha rhythm (8–14 Hz) are replaced by theta (4–7 Hz) or delta (1-4 Hz) frequencies
- this slowing is associated with diverse neurological problems including TBI, tumor, and prior surgery site
5
Q
What is scalp EEG used for
A
- to measure abnormal activity (seizures, or brain death) in intensive care, or after surgery
6
Q
What is amplitude integrated EEG (aEEG) used for?
A
- it used for monitoring brain function continuously in situations like neonatal intensive care units (NICU)
7
Q
If a patient has a suspected seizure, what is done to diagnose this patient?
A
- EEG monitoring is typically done to diagnose this patient with epilepsy
- EEG recordings from epileptic patients typically have inter-ical (between seizures) epileptiform activity
- they have have a ‘spike and wave’ pattern and reflect pathological burst of excitatory activity
8
Q
Describe the EEG changes when a patient transitions into a seizure
A
- when patient transitions to a seizure there is often an increase in interictal ‘spikes’
- this is then followed by ictal (seizure) activity which is seen has high amplitude synchronized activity on EEG
9
Q
What are electrographic (EEG) seizures?
A
- seizure that can only detected by EEG
- so they happen without any clinical signs
10
Q
What are treatments of epilepsy
A
- medication to restore excitation/inhibition balance (typically first option, and work in most cases)
- in focal medication-resistant epilepsy, surgery is often an option
11
Q
What is the difference between focal and generalized epilepsy?
A
- focal epilepsy stats in one location/hemisphere, whereas in generalized epilepsy seizures seem to start in multiple locations and/or bilaterally
12
Q
What are the causes of epilepsy
A
- channelopathies can lead to excess excitation
- focal dysplasia caused by abnormal neural migration can lead to excess excitation
- mechanical pressure due to tumor growth can cause seizures
13
Q
What are the main steps in the epilepsy surgery workflow
A
- monitor a scalp EEG, determine wether there is epileptiform activity (seizures or spikes) and determine wether the seizure is ‘focal’ (i.e. lateralized)
- if epiletiform activity present determine wether anti-epileptic medication work, if not consider surgery
- if focal, localize epileptogenic region by using MEG, MRI or Semiology and localize ‘eloquent’ cortex using fMRI or MEG
- then implant iEEG to localize epileptogenic cortex and eloquent brain areas
- plan to reset epileptogenic areas while sparing ‘eloquent’ brain regions
14
Q
Surgery is only considered if we can…
A
- can we locate the epileptogenic (seizure causing) cortex
- can we remove it without injuring eloquent cortex
15
Q
What are several types of evidence that is considered before surgery to determine where seizures stars?
A
- MRI - is their a lesion?
- neuropsychology - do deficits indicate lesion location
- MEG - where do interictal spikes originate? Where is eloquent cortex
- fMRI - where is eloquent cortex?
- Semiology - what does the seizure look like clinically
16
Q
detection and diagnosis of epilepsy
A
- scalp EEG can be collected if brain abnormalities are suspected such as epilepsy, abnormal development due to brain damage
- typically done by visual inspect of hours of EEG by a neurophysiologist
17
Q
Where can brain abnormalities be suspected on an EEG
A
medial temporal lobe
18
Q
MEG in epilepsy (over EEG)
A
- it records magnetic activity, providing higher spatial resolution
- it used for the most accurate noninvasive mapping of neurophysiology, and clinically to guide epilepsy surgery
- it is most commonly used to localize interictal spikes to localize epileptogenic regions
19
Q
What technology is used to localize interictal spikes and why?
A
- MEG is used to localize interictal epileptic spikes to localize epileptogenic areas
20
Q
Why are spike clusters important and what do they do?
A
- they localize epileptogenic cortex
- provides surgical guidance
21
Q
How does MEG to localize functional areas pre-surgery
A
- by mapping neurophysiological responses to anatomy (MRI)
- for example, gamma (>30 Hz) responses can be used to localize primary motor and somatosensory areas by using median nerve stimulation
22
Q
How do fMRI and MEG localize expressive language
A
- verb generation paradigm: subjects see pictures of items and think of verbs associated with them
23
Q
What form of localization reveals the area responsible for language production
A
- beamformer localization reveals regions responsible for language production
24
Q
How do we localize higher function
A
- MRI and MEG can localize higher functions by averaging neurophysiological activity for many trials for a cognitive task so we can localize relevant areas
- for example, MEG activation in language tasks can localize eloquent cortical areas responsible for speech to guide surgery
25
What is an iEEG? Why is it used?
- intracranial EEG involves electrodes surgically implanted into the human brain
- typically subdural electrodes grid on cortical surface or stereotaxic electrodes into radiographic lesion
- it is used in drug-resident focal epilepsy to localize epileptogenic cortex and eloquent cortex
26
How is iEEG used to map epileptogenic cortex
- iEEG is implanted fir about a week to capture multiple seizures
- clinical neurophysiologists look for high frequency oscillations and fast rhythmic discharges
27
HFO's as markers of epileptogenic cortex
- HFO's ( >80 Hz, high gamma) are markers for epileptogenic cortex
- analyzing connectivity patterns throughout seizures may reveal seizure dynamics
28
Mapping eloquent cortex using iEEG
- neurophysiologist can stimulate nerves (i.e median nerve) to observe electrical responses in the brain
- they can also stimulate electrodes to observe behaviours (language mapping)
29
Cortical anatomy of consciousness
The core 'consious network' includes the medial prefrontal cortex and the posterior parietal cortex which overlaps DMN
30
What are the characteristics of absent seizures (petit mal)
- absent seizures (petit mal) are characterized by periods of staring, inattentiveness and disruption of consciousness
31
What does the fMRI reveal during absent seizures
- ictal activation spreading to encompass cortical consiousness network
- activation spreads to thalamus
- deactivation in cortical consciousness networks
32
What are grand mal seizures?
- they are tonic clonic seizures typically involve a 'tonic' phase characterized by rigidity and 'clonic' phase characterized by convulsion (shaking)
- also involve loss of consciousness
33
Studies of fMRI during tonic-clonic seizures reveal
- decreased connectivity with pre-frontal cortex, cingulate gyrus, and parietal lobes
- increased connectivity between thalamus and cerebellum
34
All brain injuries result in a loss of..
- graded loss consciousness
(e.g. coma, vegetative sate)
35
Functional anatomy of a coma
- a coma is caused by reduced excitation within thalamocortical system
- due to loss of excitatory input from cholinergic brainstem nuclei which normally excite the thalamus and cortex
- due to dysregulation of inhibition involving basal ganglia furthersupressing cortical activation. (Ex. excess inhibitory output from GPi)
36
Brain network connectivity associated with level of consciousness
- resting state fMRI recorded in controls and people with disorders of consciousness
- less consciousness implied weaker connections in resting state areas (DMN)
- therefore connectivity in DMN areas vary with consciousness levels
