Lecture 3: Epilepsy and Neuroplasticity

What is epilepsy classified as?

brain disease

Definition of epilepsy

chronic medical condition produced by temporary changes in the electrical function of the brain, causing seizures which affect awareness, movement, and/or sensation

% of the population affected by epilepsy

0.5-1%

Who is most affected by epilepsy

children and the elderly

Duration of epilepsy

chronic- can be life long, or a few years

What type of population distribution does epilepsy have?

bimodal for age

Simply, what happens to brain waves causing seizures?

big synchronisation of waves of activity → seizures

Cause of epilepsy

idiopathic

• no single cause

• often no known clear cause as to why sm1 is experiencing epilepsy and why they are at a specific time

Factors that may cause epilepsy

brain injury, swelling in brain, hydrocephalous

What determines epilepsy symptoms?

type of epilepsy and location of epileptic activity

Is a diagnosis of ‘epilepsy’ that useful?

• no

• not very informative or useful

• b/c heterogeneity of disease types

• affect individual differently

• require treatment/adjustment in different ways

Two main subtypes of epilepsy

• partial

• generalised

(big distinction between two)

Partial epilepsy

not involving whole brain

Generalised epilepsy

involving much wider range of functions

What does knowing the type of epilepsy enable?

knowing type of seizure, when might happen, why might happen, what is required

Partial epilepsy: seizures

• simple partial seizures

• complex partial seizures

Generalised epilepsy: seizures

• grand mal seizures

• petit mal seizures

Simple partial seizures: neural level

• localised to specific areas of brain

• problematic electrical activity, overly synchronised waves of neurons → only in one part of brain

Simple partial seizures: effects

• localised effects according to localisation of epileptiform activity

• usually sensory and/or motor

Jacksonian March

• simple partial seizures

• wave of sensation travelling down arm

• localised jerking beginning in hand and progressing to clonic movements of entire arm (focal motor seizure))

• produced by epileptiform activity in the motor cortex that controls the arm

  → can infer movement in seizure activity and spread re sensory and motor changes in arm

What does this describe:

“localised jerking beginning in right hand and progressing to clonic movements of entire right arm”

partial epilepsy > simple partial seizure > Jacksonian March

Complex partial seizures are also referred to as…

• focal onset impaired awareness seizures

• temporal lobe epilepsy

Complex partial seizures: neural level

• partial

• localised to specific brain areas

• common localisation in temporal lobe (about 50% adult epileptics are complex partial, temporal lobe)

Complex partial seizures: effects

• associated with apparently ordered/ co-ordinated, but inappropriate, motor behaviour

  • e.g.: running, chewing, buttoning

• may be absent (impaired consciousness)

  • partial consciousness, moving about, awareness impaired

  • could know someone is speaking but be unable to respond

• lasts a few mins

• often no memory of episode

• quick recovery time

• focus on impaired awareness, but some motor symptoms

• no running awareness through period of seizure even though may appear quite normal

Earliest start point of partial seizure

aura

What do auras precede?

partial seizures

Aura: definition

abnormal sensations, e.g.:

• sense of fear, doom

• rising feeling in abdomen

• strange tastes or odours - ‘metallic’

• sensory disturbances

• visual sensations akin to hallucinations

Cause of aura

• abnormal electrical activity originating from seizure focus

• epileptic activity starts to increase before huge waves → low level changes

What are petit mal seizures also referred to as?

absence seizures

Petit mal seizures: neural level

• can involve entire brain

• large area of brain disrupted by seizure activity

• generalised

• whole brain, but at quite low level

What can petit mal seizures appear like?

conscious seizures

Petit mal seizures: effects

• person briefly ‘absent’

• disrupted consciousness

• very brief, sometimes just 1 sec

• may look like zooming out

• can have some eye or lip movement resembling normal movement

• able to maintain stream of dialogue sometimes

• unaware

• gaps - like a pause button

Petit mal seizures + school children

• can be seen as daydreaming, not paying attention

• miss things in class and be unaware

• unaware during brief absence seizure episodes

• difficult to pick up on

• important to diagnose and pick up early on

Why is absence different to partial seizure?

can’t do any level of interaction

Which two seizure types have high overlap?

petit mal and complex partial

Petit mal most common in…

• children

• tends to subside or reduce after puberty

Grand mal seizures: neural level

• can involve whole brain

  • usually does to some level

• generalised

Grand mal seizures aka as…

tonic clonic seizures

Tonic phase

rigidly extend limbs

Clonic phase

jerks in all extremities

Grand mal seizures: effects

• may lose consciousness and/or fall to ground

• rigidly extend all limbs (tonic phase)

• then have jerks in all extremities (clonic phase)

• tend to make more of impact bc of nature of it

Commonality of grand mal seizures

• less common than other types

• lot of epilepsy not this

Are types of epilepsy mutually exclusive?

no

Further spreading of epileptic activity

• partial seizures can generalise

• can begin w/ partial seizures that then becomes generalised epilepsy

What does this show?

• partial seizure generalising

• in focal: normal in 1 and 2, abnormal in 3 and 4

• after a while, may spread, so abnormal in 1,2,3,4

• referred to as focal with secondary generalisation

• can also spread to thalamus, and via the thalamus

Thalamus

big group of nuceli at base of brain, relay station

What does this show?

• generalised seizure

• primary generalised seizure

• abnormal in 1,2,3,4

How do seizures generalise?

• capacity for seizure activity to spread and spread through major connecting pathways in brain

• can spread to/via the thalamus

• big white matter pathways linking millions of neurons

• seizure activity in group of neurons > neurons connected to other groups of neurons through axons/white matter pathways > seizure activity can transfer across

• transfer pathways = (usually) big white matter pathways

• connection between left and right hemisphere- corpus callosum- enables spread

Transfer pathways

usually big white matter/ myelinated axon pathways linking millions of neurons

What is white matter made up of?

myelinated axon pathways