Epilepsy and `Neurospasticity

Define Epilepsy

A chronic medical condition produced by temporary changes in the electrical function of the brain causing seizures with affect awareness, movement or sensation.

• Affects 0.5-1% of pop.

• Idiopathic disease

• Symptoms depend on type and brain area affected.

Two types and subtypes of epilepsy

Partial - simple and/or complex Partial Seizures

Generalised - Grand and/or Petit Mal Seizures

Simple Partial Seizures

-              Localised to specific areas of the brain (partial).

-              Accordingly, localised effects that are usually sensory and/or motor.

E.g. localised jerking beginning in right hand and progressing in colonic movements i.e. jerks of entire right arm (a focal motor seizure).

This progression up the arm is produced by epileptiform activity in the motor cortex that controls the arm.

Complex Partial Seizures

-              Localised to specific areas of the brain (partial).

-              Called ‘complex’ because their effect are complex and diverse. AKA focal onset impaired awareness seizures/temporal lobe epilepsy.

-              May be associated with apparently ordered/co-ordinated, but inappropriate motor behaviour. E.g. running, chewing.

Lasts a minutes, often no memory of episode, approx. 50% of all adult epilepsies.

Explain what an aura is

Symptoms preceding partial seizures (abnormal sensations) including:

• Sense of fear

• Rising feeling in the abdomen

• Strange tastes or odours, often ‘metallic’

• Visual sensations (akin to hallucinations)

Petit Mal (absence) seizures

-              Can involve entire brain.

-              The person is briefly ‘absent’ disrupted consciousness (may not know they were absent).

-              More common with children, often disappear with age.

Probably widely under diagnosed

Grand mal Seizures

-              Can involve entire brain.

-              Patient may lose consciousness, fall to the ground, rigidly extend all the limbs (tonic phase), then have jerks in all extremities (colonic phase).

-              Tonic-colonic seizure or ‘grand mal’.

Partial Epilepsy seizures can become Generalized Epilepsy.

Brain Activity During a Seizure

• Extensive synchronisation of firing across a large number of neurons

• Can be seen by EEG measures, as well as via other invasive measures, including cell-specific recording.

• EEG used to measure/diagnose

E.g. ‘Spike and Wave’ (at 3Hz) associated with petit mal generalised seizures.

Treatments of Epilepsy

• Pharmacological - carbamazepine, phenobarbital, phenytoin
  (Dilantin), valproic acid.

• Drugs that target GABA or Na+ channels.

• The above strategies seek to dampen down the excessive neural firing.

• Surgery (in some cases).

Define Neuroplasticity

• Changes to brain structure, connectivity and function over time in response to changing environment (internal or external).

•  Akin to ‘evolution’ in the sense that what already exists is modified to better suit requirements.

Define Neurodegeneration

Neurons don’t die with age - but the connections do - others are made stronger.

• Results from a disruption to the homeostatic environment within and surrounding the neuron.

• Grey matter volume (cell bodies) do decline with age though, due to a reduction in connections and numbers of other support cells (e.g. glial cells, etc).

• White matter volume increases for a while as the connections get better insulated with myelin - connections to/from frontal cortex amongst the last to become fully myelinated.

• E.g. anterograde, retro grade and trans-neuronal degeneration.

Neuronal Death

-              Disruption of normal neurotransmitter function.

-              Loss of ‘fuel supply’ (oxygen, glucose).

-              Attack from infection, toxins or own immune system.

-              Faulty genetic signalling.

-              Physical injury.

Necrosis - Death due to cellular ill health (unmanaged).

Apoptosis - The Cellular Self Destruct Option (adaptive).

Neural Regeneration

There is clear capacity for regrowth/regeneration in the PNS but is more complex/difficult in the CNS

Regrowth

Not always helpful - if pathway is messed up Swann cells are not able to guide properly.

Implications for Spinal Cord Injury

Treatment strategies tend to focus on guiding regrowth and enhancing the tissue environment.

Trying to support or replicate the existing PNS strategies.

Neural Reorganisation

• After damage to the ‘maps’ in the brain, hey need to be reconfigured.

• In the case of damage to the body (e.g. loss of a limb), the neural system loses input, but the cells/structures are still intact and connected to the rest of the nervous system.

• This can create problems, such as phantom limb pain.