02-10-23 - Sleep, wakefulness, epilepsy and EEG Flashcards
Learning outcomes
- Recall the way EEGs are measured and the limitation sof the technique
- Recall the stages of sleep and the associated neuronal activity for each stage.
- Explain the terms ‘slow wave’ and ‘rapid eye movement’ (REM) sleep
- Understand and explain the role of the Thalamus in sleep
- Know what epilepsy is, and the classification of seizures
- Understand the range of anti-epileptic drugs and their mechanism of action
How is sleep usually described?
What are the 2 forms of unconsciousness?
What are the 3 states of consciousness?
- Sleep is usually described in relation to consciousness as an:
1) Easily reversible state of inactivity with a
2) Lack of interaction with the environment. - 2 forms of unconsciousness:
1) Coma (depressed state of neural activity)
2) Sleep (variation in neural activity) - 3 states of consciousness (Antonio Damasio):
1) Wakefulness – animal is alert, detects objects and pays attention to them
2) Core consciousness –wakefulness plus emotional responses, and simple memory.
3) Extended consciousness – all of the above plus self awareness, autobiographical memory, language and creativity.
How many vertebrates and mammals sleep?
What are 3 possible functions of sleep?
What is neuronal activity like during sleep?
What is oxygen consumption like during sleep?
What are the 2 main forms of externally discernible sleep?
How can neuronal activity during different stages of wakefulness (including sleep) be measured?
- Most vertebrates, and all mammals sleep, but not all sleep in the same way as humans – e.g. Dolphins vs. seals vs. humans
- 3 possible functions of sleep:
1) Processing and storage of memories
2) Recuperation of the body’s immune system
3) To conserve energy - During sleep the neurons of the brain are active, but display a different type of activity from wakefulness
- 2 main forms of externally discernible 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 do EEGs work? What synaptic activity is picked up on an EEG?
How does synchronisation of neurons occur?
How does synchronisation of neurons affect the peaks on an EEG?
- EEGs work by using electrodes to detect neuronal activity in the cortex below
- On an ECG:
- Post synaptic activity of individual neurons not picked up
- Post synaptic activity of synchronised dendritic activity can be picked up
- Synchronisation of neurons is done either by neuronal interconnections or by pacemaker
- The more neurons that are synchronised, the bigger the peaks on the EEG. (like a Mexican wave)
How are EEG electrons arranged?
How are pictures of neuronal activity developed using EEGs?
How do EEG recordings distinguish stages of sleep?
- EEG electrodes are arranged in 19 pairs (or more) at internationally agreed points on the surface of the head e.g Sylvian fissure (lateral sulcus). Central sulcus, and inion
- Comparison between the pairs of electrodes provides a coarse picture of 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 be subdivided into a further four stages of sleep, each with its own characteristic brain wave patterns.
EEG recording (in picture)
What is the deepest stage of sleep?
How long does it take to go from drowsy to deep sleep?
How long do periods of REM sleep last?
How many REM sleeps do we have per night?
What is the minimum time between REMS?
- EEG stage 4 is the deepest stage of sleep
- 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
Describe the 6 EEG defined stages of sleep.
- 6 EEG defined stages of sleep:
1) Awake
* Eyes closed, alpha High frequency (8- 13Hz), and low amp (50-µV)
* Eyes open beta waves (14-60Hz) waves of activity
* With open eyes our brain is more active
* When we are awake, there are hardly any large amplitudes/synchronisation amongst neurons
2) Stage 1
* Easily roused.
* Slow rolling eye movements.
* Some theta waves (slower frequency (4- 7Hz) & higher amplitude) waves
3) Stage 2
* Begin K complexes & sleep spindles (8- 14Hz bursts).
* No eye movement but body movement remains possible
4) Stage 3
* Has slower frequency delta waves (including amplitude)
* Harder to rouse.
* Few spindles.
5) Stage 4
* Deepest sleep, hardest to rouse.
* >50% EEG waves at 2Hz & high amplitude - called delta waves.
* Heart rate & BP lower, movement 15- 30 min period
6) REM
* Fast beta waves and REM.
* Subject easier to rouse than in stage 4.
* Dreaming, recalled, plus low muscle tone
Describe the 5 types of waves on EEGs (in picture).
Describe their frequency.
Describe what they each do
What controls the passage from stage 1 NREM (non-rem) to stage 4 NREM, and then to REM?
Describe the influence of the thalamus on brain waves during somnolence (drowsiness/strong desire to fall asleep).
- The passage from stage 1 NREM (non-rem) to stage 4 NREM, and then to REM is via the reticular formation which helps turn sleep on and off through interactions with the thalamus
- When there is excitation of the reticular formation, this leads to depolarisation (excitatory) signals to be sent to the thalamus, which leads to non-rhythmic output that increases arousal
- When there is inhibition of the reticular formation, this leads to hyperpolarisation (inhibitory) signals to be sent to the thalamus, which leads to rhythmic output and slow EEG waves in cerebral cortex, leading to sleep.
How common is epilepsy?
What is epilepsy?
How rare is sudden deaths from epilepsy?
What causes this?
Why is classification of seizure in epilepsy important?
- Epilepsy is common - affects about 1% of the population.
- It is a continuing tendency to have recurrent, unprovoked seizures.
- There is a 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 in epilepsy is important – mixture of description of attack, and investigations.
- Classification is important as some drugs make certain seizure types worse
How can we diagnose epilepsy?
What do most working diagnosis for epilepsy depend on?
What is essential in this process?
What are 4 relevant feature of history taking in epilepsy?
- 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 from any observers
- 4 relevant features of history taking in epilepsy:
1) +/- Aura/warning/fear/Deja vu from patient
* Patients feel like they know when an attack is going to occur
2) Abnormal movements (lip smacking, patting, stroking) reported by patient or witness
3) After effects? – memory loss, confusion, headache for mins or hours
4) Interictal examination is usually normal
* Interictal is the period between seizures, which is usually normal
Describe the classification of seizures flow chart (in picture)
What causes focal seizures?
Describe focal aware seizures.
What is Aura?
What are they often seen as?
What are signs of a temporal aura.
Describe the signs of focal seizures affecting the following areas of the cortex:
1) Moot supplementary or Pre-motor area
2) Primary motor cortex
3) Visual association cortex
4) Occipital lobe
5) Auditory cortex
6) Associative auditory cortex
- Focal seizures are caused when the seizure/electrical activity in the cortex can’t be controlled din a particular place
- Focal aware seizures - consciousness is preserved with positive or negative symptoms. Symptoms are related to areas affected in brain
- Aura are Brief simple partial seizures with no outward behavioural manifestation.
- Often a warning sign of larger seizure
- Temporal auras include visceral discomfort, odour, anxiety or fear
- Signs of focal seizures affecting the following areas of the cortex:
1) Motor supplementary or Pre-motor area
* Elaborate motor output
2) Primary motor cortex
* Rhythmic (clonic) movements
3) Visual association cortex
* Faces or complex scenes
* Patients feel like they can see faces/remember faces
4) Occipital lobe
* Contralateral visual hallucinations (shapes and light)
5) Auditory cortex
* Roaring or ‘underwater’ hearing
6) Associative auditory cortex
* Patients can hear music
* The more complex the sound head, the close to the processing part of this sensation
What occurs when focal seizures translate to generalized seizures?
- Focal seizure patients will only suffer effects from the effected part of the brain, but occasionally, they can transfer to generalized seizures, which encompasses both hemispheres of the cortex, so we will get activity on all fronts in all types of ways (focal to bilateral tonic clonic)
How does focal unaware compare to focal aware seizures?
Which lobe is most commonly affected?
What strictures are commonly damaged?
How long do focal unaware seizures last?
Describe the 5 stages of focal unaware seizures.
What can focal unaware seizures develop into?
- Unlike focal aware, there can be impairment of consciousness in focal unaware seizures
- Temporal lobe seizures most common (40% of all cases)
- Damage to hippocampus pyramidal cells is quite common and sclerotic tissues (scarred) act as foci - focus (plural foci) is a pathologic term describing cells that can be seen only microscopically)
- Focal unaware lesions are usually 1-2min total duration
- 5 Stages of focal unaware seizures:
1) Often begin with aura (fear, anxiety, déjà vu, olfactory sensation) linked to location
2) Unresponsiveness then
3) Automatisms (lip smacking, patting, swallowing etc) & unusual sounds (grunting)
4) Occasionally autonomic responses (Tachycardia pupil dilation)
5) Post ictal headache common, often confusion.
- Focal unaware seizures can evolve into Generalised seizures which involve the whole of the brain and which impair consciousness (focal to bilateral tonic clonic)
What parts of the brain are affected in generalized seizures?
What determines manifestations of the seizure?
What % of all epileptic Syndromes feature generalized seizures?
What feature is always present in generalized seizures?
- In generalized seizures, both hemispheres are widely involved from the outset.
- Manifestations of the seizure are determined by the cortical site at which the seizure arises, even though the whole cortex is involved
- Generalized seizures are present in 40% of all epileptic Syndromes.
- There is always an alteration to consciousness
Generalized seizures.
Describe to the 2 forms of absence seizures (petit mal seizures) – 4 features each
- Generalized seizures
- 2 forms of absence seizures (petit mal seizures):
1) Most typical
* Sudden onset (no aura) and
* Abrupt cessation
* Brief duration (20 sec)
* Attack may be associated with mild clonic jerking of the eyelids
2) Atypical
* postural tone changes,
* autonomic phenomena and
* automatisms (difficult diagnosis from focal unaware seizures);
* characteristic 2.5-3.5 Hz spike-and wave pattern
Describe myoclonic seizures.
How common is myoclonic jerking in various types of seizures?
Why are they treated differently to some extent from focal leading to generalized seizures?
Describe atonic seizures.
Describe atonic-clonic seizures (grand mal seizures)
- Myoclonic seizures are brief, shock-like jerks of a muscle or a group of muscles
- Myoclonic jerking is seen in a wide variety of seizures but when this is the major seizure type, it is treated differently to some extent from focal leading to generalized – treating Juvenile myoclonic seizures with carbamazepine will make them worse – also with absence seizures
- Atonic seizures are a sudden loss of postural tone; most often in children but may be seen in adults – generally rare.
- Tonic-clonic (grand mal) seizures are major convulsions with rigidity (tonic) and jerking (clonic), this slows over 60-120 sec followed by stuporous state (postictal depression)
- Tonic-clonic seizure in picture
EEG recordings showing various epileptic syndromes (in picture) – wont be tested
Describe 4 factors involved in the cellular mechanism of seizures (in picture).
Describe the 4 factors that are used to counter these seizure factors
- 4 factors involved in the cellular mechanism of seizures:
1) EPSPs
* Countered with IPSPs
2) Na+ influx
* Counter with K+ efflux
3) Ca2+ currents
* Countered with Cl- influx
4) Paroxysmal depolarization
* Countered with Pumps and low pH
Describe 5 targets for anti-epileptic drugs (AEDs)
- 5 targets for anti-epileptic drugs (AEDs):
1) Suppress the excitatory neurotransmitter system—by inhibiting Na channels
2) Enhance the inhibitory neurotransmitter system—GABA (Benzodiazapines)
3) Block voltage-gated inward positive currents—Na+ or Ca++
4) Increase outward positive current—K+
5) Many AEDs pleiotropic—act via multiple mechanisms
Mechanism of action of AEDs (in picture) – don’t need to learn
Describe the AED treatment options flow chart (in picture)
