In The Name of Allah The Most Beneficent The Most Merciful 1

ECE 4550: Biomedical Instrumentation Lecture: EEG Engr. Ijlal Haider University of Lahore, Lahore 2

Electro Encephalo Gram  Greek words  Encephalo (Brain)  Gram (Picture)  Picture of electrical activities of Brain

EEG  Interference pattern of many action potential  One nearer to electrode will dominate  Diagnosis are based on Empirical Study i.e. doing by reasoning

Configuration of Electrodes  Needs a standard configuration of electrodes on the brain  system is accepted worldwide  The top of head is divided into grids of 20%, 20% and 10% from the center to the sides

Configuration of Electrodes

 EEG potentials are measured between specified electrodes on this grid  Usually look for symmetry between right and left brain, this is useful in diagnosis of Brain Tumor  Look for abnormally large signals to detect Epilepsy  Epilepsy (Petit Mal and Grand Mal)

Typical EEG Signal  Normal EEG signal  Amplitude: micro volts  Frequency content: Hz

Typical EEG Signal  Compared to amplitude when awake, amplitude increases when a person is dozing  It is because of the nature of the interference  When awake more probability of cancellation of phase (more destructive)  When dozing less probability of cancellation (constructive)

Diagnosis  Electrodes are placed on both sides of brain  Activities are measured  If both are not symmetrical then there may be something happening inside e.g. tumor

Diagnosis  Epilepsy (seizure)  Hyper activity of brain  To stimulate seizure, flashes of light are used (normally for min)

Diagnosis  Hearing test  Optic nerve test

Evoked EEG  EEG response obtained through stimulations  Audio (Ears)  Visual (Eyes)  Somatosensory (Nerves)

Audio Evoked Potentials (AEP)  Audio Stimulations or Audio Evoked Potentials (AEP)  Slow vertex response (SVR)  Brain stem electric response (BSER)

Audio Evoked Potentials (AEP)  Used for tests of hearing when subject is unable to give feedback or where there is possibilities of intentional misinformation  Objective hearing test  In contrast to subjective tests where subject’s feedback is used

Audio Evoked Potentials  Give click sound stimulation (pulses) to the ear through headphones in isolated environment preferably  Record response from the brain  In SVR or BSER configuration

Audio Evoked Potentials (AEP)  SVR  Active electrode at top of head  Reference electrode near the ear (mastoid bone)  Common electrode on forehead

Audio Evoked Potentials (AEP)  BSER  Active electrode at back of brain  Reference electrode near the ear (mastoid bone)  Common electrode on forehead

Audio Evoked Potentials (AEP)  Latency of SVR: approx. 300 ms  Amplitude; few microvolts  Needs approx. 50 averages  Latency of BSER: approx. 10 ms  Amplitude: < 1 microvolt  Needs approx averages

Hearing Test  Hearing test  Usually level of stimulation is reduced from a high value till there is no evoked response  This gives the threshold of hearing

Visual Evoked Potential (VEP)  Give different pattern of visual stimulation and record evoked potential from the “visual cortex” at the back of brain.  Reference and common electrodes are at ear and at forehead 21

Visual Evoked Potential (VEP)  Applications  Detect condition of optic nerve for each age separately  If there is tumor pressing on optic nerve, the latency of the response for the affected side will be prolonged 22

Somato Sensory Evoked Potential (SSEP)  Stimulate a sensory nerve and record from brain at the respective area  Commonly Median nerve at wrist and Tibial nerve at the ankle is stimulated 23

SSEP  Time it takes for nerve fibers to relay a stimulus from the point of stimulation (wrist or ankle) to a detection site on the scalp, neck or back can be analyzed  By analyzing the SSEP pattern, condition of sensory nerves can be detected 24

SSEP  For a disorder Multiple Selerosis the latencies on the both sides will be prolonged due to demyelination 25

SNR Improvement  Due to low amplitude signals of EEG, noise can effect the signal measurements  In order to get better Signal to Noise Ratio, a number of samples are recorded and averaged 26

Parts of Brain and Functions  3 Major Parts  The Medulla Oblongata helps in control of Autonomic Functions, Relay of Nerve Signals Between the Brain and Spinal Cord Coordination of Body Movements  The Cerebellum is involved in the coordination of voluntary motor movement, balance and equilibrium  The Cerebrum is the newest (evolutionarily) and largest part of the brain as a whole. It is here that things like perception, imagination, thought, judgment, and decision occur (consists of many lobes, links on next slide) 27

Parts of Brain and Functions  For interesting information on different parts of brain and their functions, visit  dpuzzles.com/brain_parts_ function.html dpuzzles.com/brain_parts_ function.html  /cgboer/genpsycerebrum. html (for Cerebrum in detail how it controls ) /cgboer/genpsycerebrum. html 28

Thank You! 29