Final project: Neurobiology of everyday life.

Fareda Fakhrai

Vagus nerve stimulation in epilepsy

I look after children with epilepsy and thought it would be good to start with something i know a little about.I have chosen to look at how vagus nerve stimulation (VNS) works in epilepsy as I have recently been involved in looking after a child with refractory epilepsy who will be going to have a VNS insertion.

Introduction

Epilepsy experts suggests that epilepsy is a disease of the brain defined as:

At least two unprovoked (or reflex) seizures occurring more than 24 hours apart; or

One unprovoked (or reflex) seizure and a probability of further seizures similar to the general recurrence risk (at least 60%) after two unprovoked seizures, occurring over the next 10 years; or

Diagnosis of an epilepsy syndromeILEA 2014.

What is epilepsy?

Definition of epilepsy

Epilepsy is the tendency to have seizures due to uncontrolled electrochemical activity in the brain

Definition of seizures

A seizure is a brief disturbance of consciousness, behaviour, emotion, motor function or sensation caused a disruption of the electrical communication between neurones

Neurones are nerve cells which carry information as small electrical signals. Where two neurones meet, there is a gap called a synapse. Signals cross this gap using chemicals. One neurone releases the chemical into the gap. The chemical diffuses across the gap and makes the next neurone transmit an electrical signal.

Seizures occur when there is a disturbance in this process.

Depending on which part of the brain is affected leads to the different types of seizures.If it happens only on one side of the brain, this is known as a focal (partial) epilepsy. If there are neurones misfiring on both hemispheres of the brain this is known as generalised epilepsy. Most of the time, the neurons in your brain are firing at a rate of 80 times per second; during a seizure, the neurons fire at 500 times per second (Judd, 2005)The causes of epilepsy are varied, and the cause may not be found in about half of those who suffer with epilepsy. Some known causes are infections, head injury, birth trauma, stokes, scars and tumours. Vagus nerve stimulation is considered as a treatment generally after a trail of 3 different anti epileptic drugs have failed to control the epilepsy.

Basic types of seizures

If the whole brain is affected the seizure is called “generalised”, and there is loss of consciousness, however brief

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Basic types of seizures

If only part of the brain is affected it is known as “partial” or “focal” and consciousness, though often affected, may not be lost

1. The brain and its functions

Identify the parts of the nervous system that are active in your example

Temporal lobe seizures- last 30 seconds -2minutes, Signs of temporal lobe seizures include feeling frightened, a deju vu experience, strange taste sensation, feeling of rising stomach, autonomic behaviours such as lip smacking , staring, plucking at clothes. After a temporal lobe seizure confusion and difficultly in speech may occur.

Frontal lobe seizures usually last less than 30 seconds and often happen during sleep. Signs of frontal lobe seizures may include: Moving your head or eyes to one side. Unawareness of your surroundings, or having difficulty speaking, screaming, swearing or laughing. Can be mistaken for sleep problems or mental health issues.

Parietal lobe seizures last between a few seconds and a few minutes. Signs are: having feelings of numbness, tingling, heat, pressure, electricity . Having a ‘marching’ sensation that starts in your face, goes to your hand, then your arm, and down your leg (known as Jacksonian seizure). Feeling that a part of your body is missing or doesn’t belong to you. Feeling dizzy or as if you, or the area around you, is spinning. Seeing things that are not there, or seeing things differently from how they really are. For example objects might seem too close, too far away, too large, too small, slanted, moving or otherwise not right. Having difficulty understanding spoken words or language, difficulty reading or doing simple maths.

Occipital lobe process information related to vision. Seizures include seeing things that are not there, feeling that your eyes are moving. Fluttering eyelids.

 2. The Vagus Nerve

The vagus nerve is the 10th cranial nerve. It runs from the base of the brain the medulla down through the neck , chest to abdomen. It is the longest cranial nerve and impacts on many organs. It forms part of the involuntary nervous system. It has motor and sensory fibres. The vagus nerve carries incoming information from the nervous system to the brain, providing information about what the body is doing, and it also transmits outgoing information which governs a range of reflex responses.

In the 19th century neurologist found that applying pressure to the vagus nerve via the carotid artery would help reduce seizures. In 1997 vagus nerve stimulation was approved as a treatment for refractory partial epilepsy for people over 12 years old. Vagus nerve stimulation is available as an adjunctive therapy in reducing the frequency of seizures in children younger than 12 , who are refractory to antiepileptic medication but who are not suitable for resective surgery . (Nice, 2004)

Vagus Nerve Stimulation (VNS) is a non-drug treatment for epilepsy that involves the vagus nerve to send signals to the brain. A patient has a VNS device implanted ( which is similar to a pacemaker), under the skin below the collarbone. Small electrodes run from the device and wrap around the left vagus nerve.   The aim is to help calm down the irregular electrical brain activity that leads to seizures. The stimulator sends regular, mild electrical stimulations to this nerve which travel up into the brain.

The device is programmed by the doctor or nurse to deliver these signals (or “stimulate”) at periodic intervals.

What is Vagus nerve stimulation?

To begin with stimulation is usually set to happen every 30 seconds in a 5 minute cycle. These parameters can be adjusted according to tolerance and seizure control in subsequent follow up visits. The patient or their carer have some control over the VNS. Each patient is given a magnet that activates the device when it is swiped . When the patient/carer swipes over the device the VNS turns on and delivers an extra stimulus. This enables the patient who has an aura or caregiver who sees the start of a seizure to try and stop the seizure. Magnet

The aim is to reduce the seizures over time , hopefully also reducing the medication needed and improving the person everyday quality of life.

My background is nursing which I trained in many years ago. Now I look after children with epilepsy and complex disabilities. I realise that even though I have good experience in this area, my neurobiology knowledge was indeed lacking. During weeks one and two of this course Prof. Mason explains the brain and the central nervous system brilliantly. Going over in depth about the brain has helped me understand the parts of the brain involved and the corresponding symptoms apparent when a patient is having a seizure. For instance if the seizure starts in the occipital lobe then they experience visual disturbances such as distorted images. The modules on neurocommunication has given me much clearer picture on the involvement of the neurones, and how things can go wrong.

All of Prof Mason’s weekly classes have been full of information. Leading me to further explore areas I may not have done before. However I am more conscious of the need to further continue study and even go back over this course to cement what I have already learnt.

Explain in detail the ways in which this course has allowed you to better analyze the events and phenomena around you

http://www.healthline.com/human-body-maps/vagus-nerve

http://epilepsy.med.nyu.edu/diagnosis-treatment/vagus-nerve-stimulation-vns#sthash.g8cPjsde.dpbs

Judd, Sandra J., ed. "Brain Disorders Sourcebook, Second Edition." Health Reference Series. Omnigraphics. 2005.

http://publications.nice.org.uk/the-epilepsies-the-diagnosis-and-management-of-the-epilepsies-in-adults-and-children-in-primary-and-cg137/guidance#vagus-nerve-stimulation-vns

http://www.ilae.org/Visitors/Centre/Definition-2014.cfm

References