EEG records electric potentials from the brain using electrodes on the scalp. It can measure spontaneous brain activity as well as evoked potentials in response to stimuli. EEG uses Ag-AgCl electrodes applied to the scalp with gel to reduce impedance, connected to an amplifier, computer, and software for processing, artifact removal, data interpretation, and storage. EEG can diagnose epilepsy and other neurological disorders, study cognitive processes, and has high temporal resolution, but suffers from low spatial resolution and potential artifacts corrupting the data.

1. EEG/MEG/ERP

2. Electroencephalography (EEG)
• An imaging technique to record electric
potentials due to neuronal activities using
electrodes over the scalp.
• Spontaneous activity
– Goes on continuously (~ 100 µV )
• Evoked Potentials
– Response to stimulus (electric, auditory, visual, etc.)
– Very low Signal-Noise ratio
• Normally in the order of micro volts
• Bandwidth of less than 50 Hz

3. Apparatus
• Electrodes
– Ag-AgCl electrodes with gel to reduce
impedaance
– 10/20 system electrode cap
• Amplifier
– Amplifier
– Filter
– Sampling and ADC
• Computer
– Software
• Filtering and signal processing
• Artifact removal
• Identification of abnormalities
• EP identification
• Data interpretation
– Visualization
– Data Storing
Fig 01: 10/20 system of electrode
positioning

4. Signal interpretation
• Delta (0.5-4 Hz)
– Slow wave sleep
– Pathalogical if in waking adults
• Theta (4-8 Hz)
– During sleep
• Alpha (8-12 Hz)
– Visual information processing
• Beta (13-30 Hz)
– tranqualizers
• Gamma (30-50 Hz)

5. Applications/
Advantages/Disadvantages
• Applications
– Diagnosis of epilepsy, sleep disorders, strokes, head trauma,
encephalopathies
– Study cognitive processes (perception, memory, attention,
language, emotion,etc.
• Advantages
– High temporal resoluton
– Noninvasive
– Inexpensive
– Fast and easy electrode placing
– Minimal patient discomfort
– Highly available
• Disadvantages
– Low spatial resolution
– Possible corruption of data due to artifacts and interferences
– Inverse problem almost impossible