Report Eeg

8/13/2019 Report Eeg

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Objectives:-

TO Record the EEG waveform of a given human subject from skull for four

different positions of the electrodes and analized the different frequency band

using single channel for two conditions

Relaxed with eyes open.

Relaxed with eyes closed .

Apparatus Required:-

BIOPAC Electrode Lead Set x 2 (SS2L)

BIOPAC Electrode Gel (GEL1) and Abrasive Pad (ELPAD) or Skincleanser or alcohol prep

BIOPAC Student Lab System: BSL 4 software,MP45 hardware

Computer System (Windows 7, Vista, XP, Mac OS X 10.510.7)

Theory:-

Electroencephalography is a medical imaging technique that reads scalp electricalactivity generated by brain structures. The electroencephalogram (EEG) is defined as

electrical activity of an alternating type recorded from the scalp surface after beingpicked up by metal electrodes and conductive media .

The EEG measured directly from the cortical surface is called electrocortiogram whilewhen using depth probes it is called electrogram. In this article, we will refer only to

EEG measured from the head surface. Thus electroencephalographic reading is acompletely non-invasive procedure that can be applied repeatedly to patients, normal

adults, and children with virtually no risk or limitation.When brain cells (neurons) are activated, local current flows are produced. EEG

measures mostly the currents that flow during synaptic excitations of the dendrites ofmany pyramidal neurons in the cerebral cortex. Differences of electrical potentials are

caused by summed postsynaptic graded potentials from pyramidal cells that createelectrical dipoles between soma (body of neuron) and apical dendrites (neural

branches). Brain electrical current consists mostly of Na+, K+, Ca++, and Cl- ionsthat are pumped through channels in neuron membranes in the direction governed by

membrane potential. The detailed microscopic picture is more sophisticated, including


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different types of synapses involving variety of neurotransmitters. Only large

populations of active neurons can generate electrical activity recordable on the headsurface. Between electrode and neuronal layers current penetrates through skin, skull

and several other layers. Weak electrical signals detected by the scalp electrodes are

massively amplified, and then displayed on paper or stored to computer memory [3].Due to capability to reflect both the normal and abnormal electrical activity of the

brain, EEG has been found to be a very powerful tool in the field of neurology andclinical neurophysiology. The human brain electric activity starts around the 17-23

week of prenatal development. It is assumed that at birth the full number of neural

cells is already developed, roughly 1011

neurons . This makes an average density of

104

neurons per cubic mm. Neurons are mutually connected into neural nets through

synapses. Adults have about 500 trillion (5.1014

) synapses. The number of synapses

per one neuron with age increases, however the number of neurons with age

decreases, thus the total number of synapses decreases with age too. From theanatomical point of view, the brain can be divided into three sections: cerebrum,cerebellum, and brain stem. The cerebrum consists of left and right hemisphere with

highly convoluted surface layer called cerebral cortex. The cortex is a

Fig-1


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dominant part of the central nervous system. The cerebrum obtains centres for

movement initiation, conscious awareness of sensation, complex analysis, and

expression of emotions and behaviour. The cerebellum coordinates voluntary

movements of muscles and balance maintaining. The brain stem controls

respiration, heart regulation, biorythms, neurohormone and hormone secretion,

etc.[5]. The highest influence to EEG comes from electric activity of cerebral

cortex due to its surface position

Four simple periodic rhythms recorded in the EEG are alpha, beta, delta, andtheta. These rhythms are identified by frequency (Hz or cycles/sec) and amplitude

Alpha

The four basic rhythms have been associated with various states. In general, thealpha rhythm isthe prominent EEG wave pattern of an adult who is awake but

relaxed with eyes closed. Eachregion of the brain has a characteristic alpha rhythm

but alpha waves of the greatest amplitude are recorded from the occipital andparietal regions of the cerebral cortex. Results from various studies indicate that:

females tend to have higher mean frequencies of alpha waves than males

alpha wave amplitudes are likely to be higher in outgoing subject.

alpha wave amplitudes vary with the subjects attention to mental tasks

performed with the eyes closed

In general, amplitudes of alpha waves diminish when subjects open their eyes and

are attentive to external stimuli although some subjects trained in relaxationtechniques can maintain high alpha amplitudes even with their eyes open.


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BetaBeta rhythms occur in individuals who are alert and attentive to external stimuli orexert specificmental effort, or paradoxically, beta rhythms also occur during deep

sleep, REM (Rapid EyeMovement) sleep when the eyes switch back and forth.

Notice that the amplitude of beta rhythmstends to be lower than for alpha rhythms.This does not mean that there is less electrical activity,rather that the positiveand negative activities are starting to counterbalance so that the sum of the

electrical activity is less. Thus, instead of getting the wave-like synchronizedpattern ofalpha waves, desynchronization or alpha block occurs. So, the beta

wave represents arousal ofthe cortex to a higher state of alertness or tension. It mayalso be associated with remembering

or retrieving memories.

Delta and Theta

Delta and theta rhythms are low-frequency EEG patterns that increase during sleep in thenormal adult. As people move from lighter to deeper stages of sleep (prior to REM

sleep), the occurrence of alpha waves diminishes and is gradually replaced by the lower

frequency theta and then delta rhythms.

Although delta and theta rhythms are generally most prominent during sleep, thereare cases when delta and theta rhythms are recorded from individuals who are

awake. For example, theta waves will occur for brief intervals during emotional

responses to frustrating events or situations. Delta waves may increase during

difficult mental activities requiring concentration. In general, the occurrence andamplitudes of delta and theta rhythms are highly variable within and between

individuals.EEG electrode placement technique:Proper site preparation and electrode placement are essential for clean,trouble-free recording of the EEG signal. The following steps describe howto achieve a secure connection in an efficient, repeatable way. They shouldbe followed closely every time EEG is recorded. This may seem dauntingat first, but the technique is easily learned and the user will quickly becomeaccustomed to it and will certainly appreciate the benefits .1020 electrode placement system

The tentwenty (1020) electrode system of the International Federation isthe standard for electrode placement. It is used to place surface EEGelectrodes in a repeatable way independent of inter-patient anatomicalvariability. Called 1020 because of the way distances between electrodesites are computed. The distances between certain anatomical landmarksare segmented at increments of 10% and 20% of their value, andelectrodes are placed at these points.


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A letter is used to indicate over which area of the brain the site is located.Sites are identified as follows:

Other miscellaneous labels are used for the ears (A) and other referencesites (for example, M for mastoid process, G for ground, etc.). The letter Zindicates the central line along the interhemispheric fissure.Numbers are used to indicate the position in reference to the central line(Z). Number value increases the further away a site is from the central line.Odd numbers are on the left. Even numbers are on the right .

Locate the inion


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On the posterior base of the skull, where the spine meets the skull, there isa small protrusion called the inion. It can be found by running the fingerup the spine towards the skull.There is a small crevice between the spine and skull in which vertebrae canno longer be felt. Just above that area, the inion of the skull can be found.

Locate the nasion

The depression on the bridge of the nose, just below the brow and directlybetween both eyes, is called the nasion.


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The line between these two points runs along the interhemispheric fissureof the brain (the space that separates the left and right sides of the brain,i.e. right down the middle).

Mark a spot located at 50% of the distance between the nasion and theinion.

Locate the mandibular notch

To locate the mandibular notch, place a finger against the tragus, justanterior to the ear, and ask the subject to open their mouth. Your fingershould find its way into a cavity, resting superior to the manibular notch.Find this spot on both sides of the head.


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The line that connects the left and right mandibular notches runs along thecentral sulcus of the brain (the space that separates the frontal and parietallobes).

Mark a spot located at 50% of the distance between the left and rightmandibular notches. It should intersect directly with the mark madebetween the front and back of the head.The intersection of these two lines is electrode location CZ.

Along the line between the mandibular notches, 20% of the total distancetowards the left is location C3, 20% towardsthe right is location C4.


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For single channel recording we will consider the following positionsPosition 1 O1 A1Position 2 O2 A2Position 3 P1 A1Position 4 - P2 A2Nasion point is taken as the reference point while connecting the

electrode and lead system.

PROCEDURE:-

To record the EEG signal we will connect the three electodes and leads

system by following four ways.

Connect lead 1 to the A1 position and lead 2 to the O1 position andlead 3 is connected to nasion for reference .

Connect lead 1 to A1 position and lead 2 to O2 position and lead three

to nasion for reference.

Connect lead 1 to A2 position and lead 2 to P1 position and lead 3 tonasion for reference.


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Connect lead 1 to A2 position and lead 2 to P2 position and lead 3 to

nasion for reference .

For each cases we will record the signal using BioPack student lab 4.0

software for analysis.

RESULT-

After recording the signal we will obtained the following result which

is shown in the following table.

DOMINANTFREQUENCY

POWER

0-4 HZ

4-8HZ

8-13HZ

13-30HZ

DISCUSSION-

From the above table we can see the variation in Alfa , Beta ,Gamma , Delta and

Theta waves for different condition of subject for example in the case of eye openwe will get the Alfa waves but in case of eye closed Alfa waves gets disappear.


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Report Eeg