Sleep, wakefulness, epilepsy and EEG Flashcards
What is sleep and consciousness
Sleep is usually described in relation to consciousness
- As an easily reversible state of inactivity with a lack of interaction with the environment
Unconsciousness is an inconsistent term - Can be coma (depressed state of neural activity), sleep (variation in neural activity)
Consciousness has been described as having 3 states;
- Wakefullness (animal is alert, detects objects and pays attention to them)
- Core consciousness (wakefulness plus emotional response, and simple memory)
- Extended consciousness - all of the above plus self awareness, autobiographical memory, language and creativity
What is sleep?
Sleep;
Most vertebrates, and all mammals sleep, but not all sleep in the same way as humans — e.g. Dolphins vs.
seals vs. humans
The true function of sleep is unknown:
suggested functions include the processingand storage of memories, recuperation of the bodies
immune system and to conserve energy.
During sleep the neurons of the brain are active, but display a different type of activity from wakefulness
The sleeping brain consumes as much oxygen as the wakeful brain, and sometimes more
There are two main forms of externally discernable sleep, they are either;
1) when the eyes move rapidly from side to side (REM sleep) or
2) when they do not (non REM, slow wave or deep sleep) however there are other determinants
Neuronal activity during different stages of wakefulness (including sleep) can be measured using an
Electroencephalogram (EEG)
How does EEG work?
Post synaptic activity of individual
neurons not picked up
Post synaptic activity of synchronised
dendritic activity can be picked up.
Synchronisation is either by
neuronal interconnections or by
pacemaker
The more neurons that are
synchronised, the bigger the peaks on the EEG.
(Mexican wave)
Reads through scalp, and different layers to cells in cortex
EEG electrodes are arranged in 19 pairs (or more) at internationally agreed points on the surface of the head
Comparison between the pairs of electrons provides a coarse picture for the neuronal activity in the various areas of the brain. There are numerous types of comparison used, as well as more complicated and dense networks of electrodes
EEG recordings allow the separation of REM and non-REM sleep and for the latter to subdivide into a further four stages of sleep, each with its own characteristic brain wave patterns.
What are the different stages of the EEG?
Sleep and the EEG
EEG defined stages of sleep;
Awake:
Eyes closed, alpha
High frequency (8-
13Hz), and
low am p (50-gV)
Eyes open beta
of activity.
Stage 1:
Easily roused. Slow
rolling eye
Some theta waves
(slower (4-
7Hz) & higher
amplitude) Waves
Stage 2:
Begin K complexes &
sleep spindles (8-
14Hz bursts).
No eye movement
but body movement
remains possible
Stage 3:
Has slower frequency
delta waves (inc
amplitude) appear.
Harder to rouse.
Few spindles.
Stage 4:
Deepest
sleep, hardest to rouse.
> 50% EEG waves at 2Hz &
high amplitude - called
delta waves. Heart rate &
lower,
30 min period
REM: Fast
beta waves and REM
Subject easier to
rouse than in
stage 4. Dreaming
recalled, plus low
muscle tone
From drowsy to
deep sleep takes
about 1 hour,
duration of REM
sleep is variable.
On average there
are 5 REM sleeps
per night.
Minimum time
between REM
sleeps seems to be
about 30min.
What does the brainstem reticular formation do/
The brainstem reticular formation helps turn sleep on and off through interactions with the thalamus
Hyperpolarisation starts a rhythmic excitability for slow waves seen in EEG
Slow waves entrained by thalamus then hit REM and go back around again
What are the features of Epilepsy ?
Epilepsy is common and affects about 1% of the population
Definition - a continuing tendency to have recurrent, unprovoked seizures
Rare risk of sudden death (SUDEP 1 in 1,000 epileptics) - Probably from electrical disruption in heart & patients should be informed of this
Classification of seizure type is important - mixture of description of attack and investigations
- Classification is important as some drugs make certain seizures types worse
How can you diagnose epilepsy and why do we want to know attack triggers?
Only absolute certain method to diagnose epilepsy is the measuring of cortical activity using EEG
However most working diagnosis depends on understanding the characteristics of the different types of attack
History taking is essential, both from patient and any observers
Relevant features;
- +/- Aura/warning/fear/Deja vu from patient
- Abnormal movements (lip smacking, patting, stroking) reported by patient or witness
- After effects ? - memory loss, confusion, headache for mins or hours
- Interictal examination is usually normal
How do we classify seizures?
Classification of Seizures;
Focal;
- Focal aware (person aware and conscious)
- Focal unaware (altered state if consciousness)
Can get focal to bilateral tonic clonic
Generalised Seizures;
- Absence (typical absence or atypical absence)
- Myoclonic
- Tonic
- Clonic-tonic
- Atonic
Unclassified seizures
What are the features of Focal Aware seizures?
Focal aware;
- Consciousness is preserved with +ve or -ve symptoms. Symptoms are related to areas affected in brain (see image attached for this)
Often preceded by an Aura - brief simple partial seizure with no outward behavioural manifestation. Often a warning sign of a larger seizure. Temporal auras include visceral discomfort, odour, anxiety or fear
What are the features of Focal Unaware Seizure’s?
Focal unaware;
* Unlike focal aware, there can be impairment of consciousness.
- Temporal lobe seizures most common (40% of all cases)
- Damage to hippocampus pyramidal cells is quite common and sclerotic tissues (scarred) act
as a foci - Stages of Focal unaware. Usually 1-2min total duration
- Often begin with aura (fear, anxiety, déjå vu, olfactory sensation) linked to location
Unresponsiveness then;
* automatisms (lip smacking, patting, swallowing etc) & unusual sounds (grunting)
* Occasionally autonomic responses (Tachycardia pupil dilation)
* Post ictal headache common, often confusion.
These can evolve into Generalised seizures which involve the whole of the brain and which impair
consciousness
What are the features of Generalised Seizures ?
In generalised seizures, both hemispheres are widely involved from the outset
Manifestations of the seizure are determined by the cortical site at which the seizure arises
Present in 40% of all epileptic Syndromes
There is always an alteration to consciousness
What are the features of Absence Seizure’s?
Generalised Seizures - Absence Seizures (petit mal);
Two forms, most (typical) are;
- Sudden onset (no aura)
- Abrupt cessation
- Brief duration (20 sec) (Too long for daydream and no recollection of it)
- Attack may be associated with mild clonic jerking of the eyelids
More atypically;
- Postural tone changes (can slump and fall)
- Autonomic phenomena
- Automatisms (difficult diagnosis from focal unaware seizures)
- Characteristic 2.5-3.5 Hz spike and wave pattern
What are the features of Myoclonic seizures?
Generalised Seizure;
Myoclonic jerking is seen in a wide variety of seizures but when this is the major seizure type, it is treated differently to sone extent from focal leading to generalised - treating Juvenile myoclonic seizures with carbamazepine will make them worse!
What will happen if you treat Juvenile myoclonic seizures with carbamazepine?
YOU WILL MAKE THEM WORSE!
What are the features of Atonic seizures?
Generalised seizure;
Atonic seizure - sudden loss of postural tone; most often in children but may be seen in adults - generally rare
What are the features of Tonic-clonic seizures (grand mal)?
Generalised seizure;
Tonic-clonic seizure (grand mal);
- Major convulsions with rigidity (tonic) and jerking (clonic), this slows over 60 - 120 secs followed by stuporous state (post-ictal depression)
How would a tonic clonic, absence and partial seizure look on an EEG?
Image
What are the targets for Anti-Epileptic Drugs?
Targets for AED’s;
- Suppress the excitatory neurotransmitter system - by inhibiting Na channels
- Enhance the inhibitory neurotransmitter system - GABA (Benzodiazapines)
- Block voltage-gated inward positive currents - Na+ or Ca++
- Increase outward positive current - K+
- Many AED’s pleiotropic - act via multiple mechanisms
What are the major anti epileptic drugs?
Current commonly used drugs;
- Sodium Valproate, but can be teratogenic (Need to make sure patient isn’t wanting to become pregnant)
- Lamotrigine
- Carbamazepine (has enzyme inducing effects so many have interactions)
- Oxcarbazepine (better tolerated)
- Levetiracetam]
- Topiramate
Older drugs less widely used;
- Phenytoin
- Ethosuxamide (mainly absent seizures)
- Phenobarbitone
- Vigabatrin (GABA enhancer)
- Tiagabine (GABA enhancer)
