Introduction of Electroencephalographic Signals

in Dementia- Part (I)Richard Chih-Ho Chou, MD

Biomedical Imaging and Electronics Laboratory

EEG Physiology

• Distrubuted neuronal networks assure correct functioning of the human brain.

• Inhibitory and excitatory feedforward and feedback processes are basic mechanisms

Basic Interpretation

• Standard 10-20 or 10-10 system• Awake and resting rhythm (8-13 Hz occipital region, visual blockin

g) rhythm (14-30) classification of frontal, widespr

ead type, and posterior type (sometimes called fast alpha variant because of visual blocking)

• γrhythm (>30), very low amplitude, technically difficult to study. Cognitive activity “dynamic”

rhythm (sharp transient of sawtooth shape and of pasitive polarity in the pccopital regions, looking at image containing visual details. Diphasic waves resemble positive occipital sharp transients [POST] of sleep)

• Mu rhythm (arch-shaped, 7-11Hz, half the frequency of beta activity, blocked by voluntary or passive movements)

EEG as a diagnostic tool of AD

• Reflect the dynamics of cortical activity up to the scale milliseconds.

• AD may show normal EEG, esp early stage• Vast majority of moderate patients show abnorm

al EEG• Monitor changes by serial recordings• Comparable diagnosis sensitivity of SPECT or ro

utine structural image (CT, MRI)

Abnormal EEG

rhythm (4-7.5 Hz) rhythm (<4 Hz)

• Epileptiform discharge (spikes, sharp waves, spike-slow complex, etc.)

Fractal Dimention

• It is possible to use fractal dimention as a tool to characterise the complexity for short EEG time series.

• Monotoneous relation between fractal dimension and the number of data points.

• A major problem is that these measures could only be calculated for stationary time series.