EE 4BD4 Lecture 11 The Brain and EEG 1

Brain Wave Recordings Recorded extra-cellularly from scalp (EEG) Recorded from extra-cellularly from surface of cortex (ECOG) Recorded extra-cellularly from deep structures (electroneurogram) 2

Brain Features 3

Cortical Fibres 4

Overview (EEG) 5

Cortical Contributions 6

7 Electrode Placement

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Amplifier Connections 11

Clinical Applications (Spontaneous EEG) Identify presence of lesions (historical) Diagnosis and monitoring of epilepsy (seizures) Sleep staging Estimation of depth of anesthesia Other organic brain disease Neuropsychiatry (depression, schizophrenia, Altzheimer) 12

Cortical Electrodes 13

Alpha Predominance 14

General Bandwidths 15

Abnormal Rythms 16

17 Closed Loop Epilepsy Treatment

18 EEG during REM Sleep

19 EEG during Stage 3 Sleep

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Additional Sleep Data Processing Sleep spindles (modulated alpha periods) and K complexes in Stage 1 – 2 Degree of correlation (time base) or coherence (frequency base) between different channels of EEG increases with depth of sleep. Higher level signal processing? Relate EEG to other recorded data (e.g. respiration rate, heart rate, SaO 2 22

Brain Evoked Potentials 23

Signal Pathway 24

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30 Other Evoked Potentials rTMS: Repetitive Trans-Cranial Magnetic Stimulation Treat severely depressed patients who are resistant to pharmacology Alternative is periodic applications of electro-shock (ECT) treatment 30% of patients respond Would like to increase percentage of responders

31 Current Commercial Machines Example Magstim

32 Clinical Treatment

33 Stimulus Waveforms

34 Magnetic Field Source: Medtronic, 2004

Instrumentation Challenges Recording Simultaneous Evoked Potentials Large magnetic field saturates electronics (coupling into electrode cable, amplifier inputs) Signals very small plus other background EEG, need repetitive stimulation for treatment and averaging Electrode heating during multiple stimuli Stimulation of scalp muscles (mV amplitudes phase locked to responses) Auditory “click” response 35

36 Electrode Materials 3s at 20Hz at 85% intensity, r = -30mm

37 rTMS Trains of Stimuli Au electrode, 3s at 20Hz at 85% intensity, trains at 0, 60, 120s

38 Systems Approach

39 Sham Response to rTMS “Clicks”

40 Muscle Responses during 10 Hz Left-sided Stimulation

Results of Day 2 Position Study (Typical Subject) 41

Using Digital Filtering 42

Using Wavelet Denoising 43

Brain Response for Sensitive Subject 44

Wavelet Denoised Response 45

Right side 1 Hz Response 46

Right Side Denoised Response 47