by Dr. Howard Ring, Lecturer and Honorary Consultant, University of Cambridge, 2005.

This article, written in note form, discusses the links between Tuberous Sclerosis, Epilepsy and Memory. It is primarily intended for medical professionals.

Overview

Over 80% of TS sufferers have epilepsy. They are frequent in TS in childhood. They often present themselves early – at 6 weeks or so after birth or just later.

There are 3 Types - Focal (localised) onset – partial, temporal, frontal – may subsequently generalise throughout the brain. Generalised onset – primarily generalised. Infantile spasms – (in up to 30% of TS sufferers) – linked to memory problems. This is an epileptic response of the developing brain to a physical disturbance. They are usually generalised and tend to diminish with age.

There is an intellectual disability in 40-50% of people with TS. This is most often in people with TS who also have epilepsy. The risks increase with factors such as the younger age at the first seizure, the difficulties in treating the seizures and the seizure type.

Memory

• Recalling of information by the brain
• Short-Term Memory (seconds) – (analogous with computer RAM)
• waking memory
• short-term retention and manipulation of information.
• Long-Term Memory – minutes and longer – (analogous with computer Hard Disk Drive)
• declarative memory (knowledge memory – memory of our lives)
• episodic
• semantic (encyclopaedic memory – what was said)
• procedural (unconscious memory e.g. Riding a bike, learning a skill)

Recall is difficult in old age with dimensia.
Changing from short to long term memory is a sensitive time – especially in TS

How are Memories Held in the Brain?

Memories are coded by changes in the connections (synapses) between brain cells and by changes in the strength of the synapse. Short-term memory equates to local changes at the synapse. Long-term memory needs new proteins to be manufactured by nerve cells (Epilepsy and TS affects this). Nerve cells use electrical currents to release chemical messengers across the synapses – leading to electrical currents in other nerve cells. Anything interfering with the electrical currents interferes with memory. Memory can also be disrupted by interference with the production by nerve cells of chemicals that change the synapses e.g. Tuberin. TS can do this. Tuberin disturbances interfere with these chemicals. Tuberin and Hamartin deficiencies both disrupt the synapses. In the absence of epilepsy there is some evidence that the higher the number of tubors present, the lower the IQ of the person affected.

Memory can be disrupted by interference with electrical currents that release chemicals.

Epileptic Seizures equate to intermittent disturbances of conciousness, behaviour, motor function and perception resulting from an abnormal cortical neuronal electrical discharge.

Epilepsy is a condition in which seizures recur, usually spontaneously. It can be triggered by sensitivity to flashing light. Epilepsy can wipe out memories, possibly before and after the seizures (for a few seconds to a few hours after). Epilepsy occurs in about 1% of the population. It is most common in the young and the old.

Intellect verses Epilepsy

People with mild learning difficulties (LD) i.e. an IQ of greater than 50 have epilepsy in 6-15% of cases. People with severe LD i.e. an IQ of less than 50 have epilepsy in 30% of cases. People with profound LD or additional brain damage have epilepsy in 50-80% of cases. Seizures don’t cause brain damage generally, but could do so in infantile spasms.

How Can Epilepsy Interfere with Memory?

Brain disturbances lead to Epilepsy. This is due to he effects themselves, psychological effects e.g. schooling, anti-epileptic agents e.g. drugs and also the stigma with epilepsy where patients are treated differently, therefore this alters the stimulations they receive and the way they grow up and the opportunities they are offered e.g. “I’ll drive you there” or “You must wear a helmet”.

Anatomy of Memory

If you get epilepsy in the Hippocampus memory will be disturbed. This can cause problems with blood flow in the brain. Epilepsy in People with Structural Brain Disturbances is characterised by multiple seizure types, an early onset, difficulty in controlling the disturbances and different seizures may be more difficult to distinguish (with the implications associated with incorrect treatment). Clinical factors are the age of the patient, the duration of the disorder, the site of the disorder, its type and the effects of drugs. The presence of LD is most strongly linked with infantile spasms. These are relatively common in TS, with an onset within the first 6 weeks after birth.

TS, Epilepsy and Autism

The presence of tubors in the temporal lobes and temporal lobe epilepsy lead to an increased chance of autism. With Primary Autism people with an IQ of greater than 55 have seizures in 12% of cases, whilst people with an IQ of less than 55 have seizures in 20% of cases. With Secondary Autism people have seizures in 60% of cases. We can thus conclude that epilepsy and autism are linked to underlying brain damage. Note that epilepsy does not cause autism and that autism does not cause epilepsy.

Autism doesn’t automatically mean poor memory. Epilepsy may be linked to poor memory since the physical disturbances of various kinds in both temporal lobes may interfere with memory. The presence of tubors in temporal lobes may cause temporal lobe epilepsy.

The Management of Epilepsy in TS

This can be by way of anti-epileptic drugs, surgery or by other treatment approaches such as vagal nerve stimulation (similar to pace-makers) or the Ketogenic diet for children under 5. There are no perfect anti-convulsant drugs.

How to Improve Memory?

Making lists and doing rehearsals can help to drive in the long-term memory. Giving several exposures will all help. There needs to be skilled education.

Electro-convulsive therapy can affect memory.

This entry was posted on Sunday, January 1st, 2006 at 12:01 pm and is filed under Research.