Epilepsy and EEG

Question 1

What is a seizure?

Answer 1

A temporary disruption of brain function due to abnormal excessive neuronal activity.

Question 2

What is epilepsy?

Answer 2

The chronic condition of repeated seizures.

Question 3

What are the different types of seizures?

Answer 3

Focal onset.
Generalised onset.
Unknown onset.

Question 4

Where do focal onset seizures originate?

Answer 4

Small groups of neurons called the seizure focus.

Question 5

How does a focal onset seizure typically begin?

Answer 5

Begins with jerking in the right hand, progressing to clonic movements of the entire right arm.

Question 6

What happens when a focal onset seizure progresses?

Answer 6

The person will enter a tonic or clonic phase.

Question 7

What happens during a tonic phase?

Answer 7

The person loses consciousness, their muscles stiffen, and they may fall to the ground.

Question 8

What happens during a clonic phase?

Answer 8

Muscles rhythmically contract and relax, causing jerking movements in the face, arms, and legs.

Question 9

What is an aura?

Answer 9

Unprovoked and often vivid sensations, such as fear, a rising feeling in the abdomen, or a particular odour.

Question 10

Where do generalised onset seizures originate?

Answer 10

Both hemispheres are involved from the onset.

Question 11

What are the two types of generalised onset seizures?

Answer 11

Motor (grand mal).
Non-motor (petit mal).

Question 12

Are generalised onset seizures preceded by an aura?

Answer 12

No.

Question 13

Are focal onset seizures preceded by an aura?

Answer 13

Sometimes.

Question 14

Who typically experience non-motor generalised onset seizures?

Answer 14

It is a typical absence seizure in children.

Question 15

What happens during a non-motor generalised onset seizure?

Answer 15

Staring.
Sudden cessation of all motor activity.
Loss of awareness but not posture.

Question 16

What happens during a motor generalised onset seizure?

Answer 16

Begins with a tonic phase lasting around 30 seconds.
Evolves into a clonic phase lasting around 1-2 minutes.

Question 17

What happens during the post ictal phase of a motor generalised onset seizure?

Answer 17

The person is sleepy and disorientated.

Question 18

What is an unknown onset seizure?

Answer 18

A seizure that cannot be identified because the person was alone when it happened or there is inadequate information to make the identification.

Question 19

What does NEAD stand for?

Answer 19

Non-epileptic attack disorder.

Question 20

What happens during a NEAD?

Answer 20

A person experiences symptoms similar to those of epilepsy but without any abnormal activity in the brain.

Question 21

What is another term for a NEAD?

Answer 21

Psychogenic non-epileptic seizure.

Question 22

What is the cause of a NEAD?

Answer 22

The causes are not fully understood but it may be associated with anxiety, depression and personality disorders.

Question 23

What does EEG stand for?

Answer 23

Electroencephalogram.

Question 24

What is an EEG?

Answer 24

A set of field potentials as recorded by multiple electrodes on the surface of the scalp.

Question 25

Why is the amplitude of EEG signals much smaller than the voltage changes in a single neuron?

Answer 25

The signal is distorted by the filtering and attenuation caused by the intervening layers of tissue and bone.

Question 26

What does an EEG primarily represent?

Answer 26

Slower voltage changes across the cell membrane.

Question 27

Why is synaptic activity in pyramidal neurons the principle source of EEG activity?

Answer 27

Pyramidal neurons are the major projection neurons in the cortex and their apical dendrites are orientated perpendicular to the cell surface.

Question 28

Explain the 10-20 system.

Answer 28

21 electrodes are placed on the surface of the scalp using the nasion and inion as reference points. Using the reference points, the skull perimeters are measured in the transverse and median planes. The perimeters are divided into 10% and 20% intervals for the electrode locations. 3 other electrodes are placed on each side equidistant from the neighbouring points.

Question 29

What is the nasion?

Answer 29

The delve at the top of the nose, level with the eyes.

Question 30

What is the inion?

Answer 30

The bony lump at the base of the skull.

Question 31

Why are generalised onset seizures driven by thalamocortical circuits?

Answer 31

These seizures disrupt normal brain activity in both hemispheres simultaneously.

Question 32

How does seizure activity spread?

Answer 32

Intense activity in the seizure focus can cause the electrical activity to spread to other brain regions, typically following the same axonal pathways as normal cortical activity.

Question 33

Which pathways can become involved in seizure spread?

Answer 33

Thalamocortical, subcortical and transcallosal pathways.

Question 34

What is the 3-Hz spike-and-wave pattern?

Answer 34

The characteristic EEG pattern of a non-motor generalised onset seizure.

Question 35

Where in the brain is the 3-Hz spike-and-wave pattern observed?

Answer 35

In all cerebral areas abruptly and simultaneously.