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March 2017
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BRAIN: Is There a Relationship between Consciousness and Epilepsy?

A serious health condition that affects 1% of the global population is epilepsy. This is a neurological disorder usually detected by EEG (electroencephalography) signals, and it has as common symptom spontaneous recurrent seizures characterized by intermittent paroxysmal and highly organized rhythmic neuronal discharges in the cerebral cortex.

 Multi-layer artificial neural networks model
Multi-layer artificial neural networks model

Epileptic seizures are caused by a large collection of neurons synchronous and abnormally discharged may occur for reasons such as trauma, oxygen insufficiency, tumors, infections and metabolic disorders. However, it is not possible to find any cause in half of the epileptic patients. Despite the fact that epilepsy is referred to as “seizure disease”, it is not correct to call seizures “epilepsy”. Seizures are symptoms, but epilepsy is a disease characterized by a recurrent seizure. Nonlinearity and a sensitive dependence on initial conditions are the requirements of the chaos. As chaos requires dependence on the initial conditions and it is unpredictable in the long run.

Consciousness, on the other hand, in the most general sense, means awareness, or the state of being aware of oneself and the surroundings. The brain is considered to be the central decision making organ of the human body. It anatomically consists of two lobes, the right and the left one, and of approximately 100 billion neural cells that are called neurons. The complexity of the neural circuit of the brain can be understood when thinking that each neuron makes about thousands of contacts with other neurons. The complexity of the neural circuit will be different for each brain and these differences may result in different brain capacities.

The studies which state that consciousness is adversely affected during epilepsy seizures have a broad spectrum. The adverse effects generally manifest as cloudy consciousness and/or decrease in the consciousness levels. The patient will become unconscious during generalized seizures and may also become unconscious during partial complex seizures.

There are many scientists who have approached this topic. Cavanna et al. (2008) tried to measure and statistically evaluate the consciousness levels and the consciousness states of the epileptic patients. Hughes (2008) discussed that information is transmitted to the brain cortex via the gamma oscillations (30-100Hz) which may be formed as alternatives to the epileptic foci in the preictal period and that the amplitude of the gamma oscillations increases when going from preictal to ictal periods. Danielson et al. (2011) used MRS (Magnetic Resonance Spectroscopy) and PET (Positron Emission Tomography) scans to examine the state of consciousness during epilepsy seizures. Foley et al. (2014) investigated the distortion of consciousness during epilepsy seizures using MEG device.

What this article brings new is an analysis of the relationship between the two, epilepsy and consciousness, by providing information on the materials (epileptic EEG data) and an evaluation of the epileptic EEG data with wavelet entropy and artificial neural networks. The epileptic EEG signal is separated into two segments, such as pre-ictal and ictal periods, and then analyzed. From the results of the analysis can be seen that the entropy values of the gamma band of two segments that are pre-ictal and ictal are significantly different. This means that during the transition between pre-ictal and ictal states exists a recognizable change and increase in the gamma oscillations. Thus, the gamma wavelet entropy (the attribute vector) value of the ictal period is larger than the pre-ictal period.

The relationship between consciousness and the gamma wave is that the gamma wave can be represented as a marker of consciousness, as well as of the subject’s evaluation of the arousing power of emotional stimuli. Thus, the gamma frequency band analysis offers a powerful tool for studying cortical activation patterns during emotional information processing.

Since entropy is the measure of order or disorder in a signal or system, the increase in the attribute vector of gamma suggests disorder increase. In conclusion, the disorder increase means an increase in the clouding of consciousness which proves that the consciousness is temporarily affected in an adverse manner during the epileptic seizure.

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Gabriela Tăbăcaru