EE 4BD4 Lecture 11

The Brain and EEG

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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)

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Brain Features

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Cortical Fibres

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Overview (EEG)

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Cortical Contributions

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Electrode Placement

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Amplifier Connections

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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

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Alpha Predominance

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General Bandwidths

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Abnormal Rythms

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Closed Loop Epilepsy Treatment

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EEG during REM Sleep

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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, SaO2

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Brain Evoked Potentials

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Signal Pathway

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Other Evoked PotentialsrTMS: 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

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Current Commercial Machines

• Example Magstim

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Clinical Treatment

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Stimulus Waveforms

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Magnetic Field

Source: Medtronic, 2004

Source: Medtronic, 2004

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

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Electrode Materials

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

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rTMS Trains of Stimuli

Au electrode, 3s at 20Hz at 85% intensity, trains at 0, 60, 120s

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Systems Approach

Ch0+

Gnd

Sample-and-hold

Unity gain buffer

HPF(1st order, C=0.1µF, R=10Meg, f0=0.16Hz)

2nd Gain (Non-inverting op-amp, 100x gain)

LPF(1st order, C=0.1µF, R=1.6k, f0=995Hz)

LabVIEWDAQ boardCh4 Output

Ch0 Input

Digital Trigger Input / Output from Magnetic Stimulator

ComputerMagnetic stimulator

Input / Output Trigger Lines

Ch0-

Gain Stage(Instrumentation Amplifier, 10x gain)

Ch0+

Gnd

Sample-and-hold

Unity gain buffer

HPF(1st order, C=0.1µF, R=10Meg, f0=0.16Hz)

2nd Gain (Non-inverting op-amp, 100x gain)

LPF(1st order, C=0.1µF, R=1.6k, f0=995Hz)

LabVIEWDAQ boardCh4 Output

Ch0 Input

Digital Trigger Input / Output from Magnetic Stimulator

ComputerMagnetic stimulator

Input / Output Trigger Lines

Ch0-

Gain Stage(Instrumentation Amplifier, 10x gain)

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Sham Response to rTMS “Clicks”

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Muscle Responses during 10 Hz Left-sided Stimulation

Results of Day 2 Position Study (Typical Subject)

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Using Digital Filtering

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Using Wavelet Denoising

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Brain Response for Sensitive Subject

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Wavelet Denoised Response

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Right side 1 Hz Response

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Right Side Denoised Response

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