Eeg basics.drjma

DR. JAMES M. ALO, RN,MAN,MAP, PHD

EEG

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Agenda • Introduction.• History.• Neural Activities.• Action Potentials.• EEG Generation.• Brain Rhythms.• EEG Recording and Measurement.

• Conditioning the Signals.• Abnormal EEG Patterns.• Ageing.• Mental Disorders.

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Introduction• The human brain activity start between 4-5

months before parental development.• The human brain represent the brain

functional side to side the status of the whole body.

• EEG signals measured from the brain of a human.

• The medium defines the path from neurons, as so called signal sources to electro nodes which are the sensors.

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studying neural functions and neurophysicological properties of the brain together with the mechanisms underlying the generation of the signals for detection, diagnosis and treatment of brain disorders and the related diseases.

Note :-

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History • Carlo Matteucci (1811–1868) and Emil Du

Bois-Reymond (1818–1896) were the first people to register the electrical signals emitted from muscle nerves using a galvanometer and established the concept of neurophysiology.

• Analysis of EEG signals started during the early days of EEG measurement. Berger assisted by Dietch (1932) applied Fourier analysis to EEG sequences.

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Central Nervous System (CNS) contains of two types from cells:-1. Nerve Cell.2. glia Cell.

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Nerve Cell :- it consists of

Axons Dendrites Cell Bodies

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Nerve cell components

(1) Axons :- Is along cylinder. Transmits an electrical impulse and

can be several meters long in vertebrates.

In animals can be several meters but in humans the length can be a percentage of millimeter to a meter .

An axonal transport system for delivering proteins to the ends of the cell exists and the transport system has ‘molecular motors’, which ride upon tubulin rails.

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(2) Dendrites :- Are connected to the axons or

dendrites of other cells. 1 nerve cell connected 10,000 other

nerve cells.

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Nerve 1

Nerve 2

Nerve 3

dendrites

Dendrites 1 Dendrites 2

Dendrites 3

impulses

connects

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Neural ActivitiesA potential of 60–70 mV with negative polarity may be recorded under the membrane of the cell body. This potential changes:-

If an action potential travels along the fibre, which ends in an excitatory synapse, an excitatory postsynaptic potential (EPSP) occurs in the following neuron.

If two action potentials travel along the same fibre over a short distance, there will be a summation of EPSPs producing an action potential on the postsynaptic neuron providing a certain threshold of membrane potential is reached.

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Note

With observation :- EEG + DC potentials = Abnormalities in the brain.DC component:- long strings of zeros or ones.

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Action Potentials (AP)

• APs are caused by an exchange of ions across the neuron membrane and an AP is a temporary change in the membrane potential that is transmitted along the axon.

• The conduction velocity of action potentials lies between 1 and 100 m/s. APs are initiated by many different types of stimuli; sensory nerves respond to many types of stimuli, such as chemical, light, electricity, pressure, touch, and stretching.

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Action potentials processes

1. The action must be more than gate threshold value.

2. Depolarization .3. Sodium gates close.4. Potassium gates open.5. Repolarization.6. Hyperpolarization.

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EEG Generation

EEG signal is measured of current flow of dendrites of neurons in cerebral context.

Brain cells active mode (get a new action potential), the cell produced within dendrites so this current generate a magnetic field (EMG) that cover over scalp.

By the anatomical of the human head we found that it consists of three main layers.

• 1-scalp

• 2-skull

• 3-brain

There are many thin layers between this prime layers.

When the human receive the action he could feel 1 % of the action, as it arrives to his brain and the other noise generated within scalp and skull.

Therefore, to feel action potential there must be a lot of active neurons can generate potential.

When the human born, he got a large number of neurons (10^11) nerve.

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Brain RhythmsBrain rhythms is depend on EEG

signals .The amplitudes and frequencies of

such signals change from one to another.

This waves from low to high (alpha , theta, beta ,delta ,gamma)

The history about found this frequencies.

Draft that show the frequencies' of this signals.(figure 1.7)

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Mahany

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EEG Recording and Measurement

Signal

EEG FMRI MEG

• EEG :- Electroencephalogram.

• FMRI:- Functional Magmatic

Resonance imaging.• MEG:- Magnetoencephalogram.

The functional and physiological changes within brain can registered by EEG,MEG and FMRI.

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The reasons of not using FMRI about using EEG,MEG

1) Time resolution of FMRI image is very low (2 frames/sec).EEG bandwidth can be viewed using EEG or MEG signal.

2) Many types of mental activities brain disorders cannot be registered using FMRI.

3) Accessibility of FMRI systems is limited and costly.

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EEG system consists of

To convert from analog signal to digital signal:- 1) Sampling.

2) Quantization. 3) Encoding.

Electrodes NeedleFiltersAmplifiers

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Characteristics of EEG signal-:

If data volume is increased then the number of bits increase.

Effective bandwidth of EEG signal approximately 100 HZ.

Minimum frequency 200 sample/sec. Higher resolution (brain

activities)=2000 sample/sec. 1 sample 16 bit

Note

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Note

Although the format of reading the EEG data may be different for different EEG machines, these formats are easily convertible to spreadsheets readable by most signal processing software packages such as MATLAB.

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Different types of electrodes-:1) Disposable (gel-less, and pre-gelled

types).2) Reusable dice electrodes (gold ,silver,

stainless steel or tin).3) Headbands and electrode caps.4) Saline based electrodes.5) Needle electrodes.

For multichannel recordings with a large number of electrodes, electro caps are often used.

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Conditioning the signals• The row EEG signal have amplitudes of

order of micro volts and contain frequency components up to 300 HZ.

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Filters • Are used to make suitable for processing

and visualization.Is divided to:-1) High pass filter:- remove distributing very low frequency components.2) Low pass filter:- remove distributing very high frequency components.

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Categories abnormal EEG patterns-:

Widespread intermitted slow wave abnormalities.

Bilateral persistent EEG. Focal persistent EEG.

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1) Widespread intermitted slow wave abnormalities:-

• which is attenuated by alerting the individual and eye opening, and accentuated with eye closure, hyperventilation, or drowsiness.

2) Bilateral persistent EEG:-• the phenomenon in different stages of impaired,

conscious:-3) Focal persistent EEG:-• these abnormalities may be in the form of distortion

and disappearance of normal patterns, appearance and increase of abnormal patterns, or disappearance of all patterns, but such changes are seldom seen at the cerebral cortex.

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Ageing • The ageing process affects the normal

cerebral activity in waking and sleep, and changes the response of the brain to stimuli.

• The charges stem from reducing the number of neurons and due to a general change in the brain pathology.

• General cause for ageing of brain may be decrease in cerebral blood flow.

• The REM duration decrease during the night.

• Dementia increases dramatically with ageing.

•

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Mental Disorders• Is divided to

Dementia

External Effects

Epileptic Seizure and No epileptic

attacks

Psychiatric Disorders

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1) Dementia • Dementia is a syndrome that consists of a

decline in intellectual and cognitive abilities this consequently affects the normal social activities, mode, and the relationship and interaction with other people. EEG is often used to study the effect of dementia; EEG signal can be used to detect the abnormality.

Dementia is classified intoCortical dementia such as Alzheimer's

disease (AD).Sub cortical dementia forms such as

Parkinson's.

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Generally Sub cortical dementias introduce less abnormality to

the EEG patterns than the cortical ones. EEG is usually used in the diagnosis and evaluation

of many cortical and sub cortical.

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2) Epileptic Seizure and Non-epileptic Attacks• Often the onset of a clinical seizure is

characterized by a sudden change of frequency in the EEG measurement.

• The abnormalities may be due to psychogenic changes, variations in body metabolism or circulstory insufficiency. The most important ones are periodic or quasi-periodic discharges related to serve CNS diseases.

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• Despite the epileptic form signals there are spikes and other paroxysmal discharges in healthy non epileptic persons. These discharges may be found in healthy individuals without any other symptoms of diseases. They may appear during periods of particular mental challenge on individuals, such as soldiers in the war front line, pilots, and prisoners.

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3) Psychiatric disorders.

• Not only can functional and certain anatomical brain abnormalities be investigated using EEG signals, pathophysiological brain disorders can also be studied by analysing such signals.

4)External Effects

EEG signal patterns may significantly change when using drugs for the treatment and suppression of various mental and CNS abnormalities. Variations in EEG patterns may also arise by just looking at the TV screen or listening to music without any attention. However, among the external effects the most significant ones are the pharmacological and drug effects. Therefore, it is important to know the effects of these drugs on the changes of EEG

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Test Purpose Preparation Post- Nursing Care

ElectroEncephaloGram

Record electrical activity of brain

Explain procedureDone by technician in a quiet roomPainlessTranquilizer & stimulant meds w/held for 24-48 hrs pre-EEGMaybe ask to hyperventilate 3-4 mins and watch bright, flashing lightMeals not w/heldKept awake night b4 test

Help client remove paste from hairAdmin prescribed meds w/held b4 EEGObserve for seizure activity in seizure prone patients.

Shockran!

“Learners’ are learning from experiences they have experienced which cannot be taught by

teachers except themselves.”- Dr. James M. Alo

Eeg basics.drjma

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