In The Name of Allah The Most Beneficent The Most Merciful

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

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

3. Electro Encephalo Gram • Greek words • Encephalo (Brain) • Gram (Picture) • Picture of electrical activities of Brain

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

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

6. Configuration of Electrodes

7. Configuration of Electrodes • EEG potentials are measured between specified electrodes on this 10-20 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)

8. Typical EEG Signal • Normal EEG signal • Amplitude: 10-50 micro volts • Frequency content: 0.1-30 Hz

9. 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)

10. 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

11. Diagnosis • Epilepsy (seizure) • Hyper activity of brain • To stimulate seizure, flashes of light are used (normally for 10-15 min)

12. Diagnosis • Hearing test • Optic nerve test

13. Evoked EEG • EEG response obtained through stimulations • Audio (Ears) • Visual (Eyes) • Somatosensory (Nerves)

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

15. 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

16. 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

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

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

19. 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. 1000 averages

20. 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

21. 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

22. 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

23. 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

24. 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

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

26. 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

27. 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)

28. Parts of Brain and Functions • For interesting information on different parts of brain and their functions, visit • http://www.brainhealthandpuzzles.com/brain_parts_function.html • http://webspace.ship.edu/cgboer/genpsycerebrum.html (for Cerebrum in detail how it controls )

29. Thank You!