I N T HE N AME OF A LLAH T HE M OST B ENEFICENT T HE M OST M ERCIFUL 1

ECE 4552: M EDICAL E LECTRONICS L ECTURE : E LECTRO E NCEPHALO G RAM Engr. Ijlal Haider Electrical Engineering Dept. University of Lahore, Lahore 2

E LECTRO E NCEPHALO G RAM 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

C ONFIGURATION OF E LECTRODES 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

C ONFIGURATION OF E LECTRODES

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)

T YPICAL EEG S IGNAL Normal EEG signal Amplitude: micro volts Frequency content: Hz

T YPICAL EEG S IGNAL 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)

D IAGNOSIS 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

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

D IAGNOSIS Hearing test Optic nerve test

E VOKED EEG EEG response obtained through stimulations Audio (Ears) Visual (Eyes) Somatosensory (Nerves)

A UDIO E VOKED P OTENTIALS (AEP) Audio Stimulations or Audio Evoked Potentials (AEP) Slow vertex response (SVR) Brain stem electric response (BSER)

A UDIO E VOKED P OTENTIALS (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

A UDIO E VOKED P OTENTIALS Give click sound stimulation (pulses) to the ear through headphones in isolated environment preferably Record response from the brain In SVR or BSER configuration

A UDIO E VOKED P OTENTIALS (AEP) SVR Active electrode at top of head Reference electrode near the ear (mastoid bone) Common electrode on forehead

A UDIO E VOKED P OTENTIALS (AEP) BSER Active electrode at back of brain Reference electrode near the ear (mastoid bone) Common electrode on forehead

A UDIO E VOKED P OTENTIALS (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

H EARING T EST Hearing test Usually level of stimulation is reduced from a high value till there is no evoked response This gives the threshold of hearing

V ISUAL E VOKED P OTENTIAL (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

V ISUAL E VOKED P OTENTIAL (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

S OMATO S ENSORY E VOKED P OTENTIAL (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 I MPROVEMENT 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

P ARTS OF B RAIN AND F UNCTIONS 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

P ARTS OF B RAIN AND F UNCTIONS For interesting information on different parts of brain and their functions, visit uzzles.com/brain_parts_func tion.html oer/genpsycerebrum.html oer/genpsycerebrum.html (for Cerebrum in detail how it controls ) 28

T HANK Y OU ! 29