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EEG Slide 05F.1 Electroencephalogram The electroencephalogram (EEG) is the electrical signal generated by the neurons in the brain electro −encephalus − electrical brain Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster) graph writing, ie. signal EEG Slide 05F.2 EEG Electroencephalography (EEG) is the measurement of electrical activity produced by the brain as recorded from electrodes placed on the scalp. EEG measurements on Scalp 100uV (scalp is highly insulating) Cortex (10mV) Depth (electrodes into brain) as part of surgery Electrical activity from brain is much more complex. In general, we see a summation of >1m neurons. Thus EEG is a ‘heuristic’ field. Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster) EEG measurement electrodes (source: wikipedia) EEG Slide 05F.3 Central Nervous System (CNS) anatomy Outside the CNS, There is the CSF: cerebrospinal fluid Skull Anatomical relationship of brainstem structures (medulla oblongata, pons, midbrain, and diencephalon (thalamus and hypothalamus)) to the cerebrum and cerebellum. General anatomic directions of orientation in the nervous system are superimposed on the diagrams. Here the terms rostral (toward head), caudal (toward tail), dorsal (back), and ventral (front) are associated with the brainstem; remaining terms are associated with the cerebrum. The terms medial and lateral imply nearness and remoteness, respectively, to or from the central midline axis of the brain. Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster) EEG Slide 05F.4 Types of EEG Two basic types of EEG signals Evoked Potentials A stimulus is provided, and the EEG response measured. Allows removing other activity by averaging “out of phase” signals. VER – visually evoked response AER – auditory evokes response Resting Rhythms – “brain waves” Mostly irregular patterns from brain, but sometimes form structured patterns that have been classified Alpha – quiet awake - 8-13 Hz Beta - intense mental activity – 14-30 Hz Theta – Children & distressed adult – 4-7 Hz Delta – Deep sleep & infancy – 2-3 Hz REM – Sleep with dreaming Abnormal patterns, such as epilepsy Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster) EEG Slide 05F.5 Resting Rhythms (a) Different types of normal EEG waves. (b) Replacement of alpha rhythm by an asynchronous discharge when patient opens eyes. (c) Representative abnormal EEG waveforms in different types of epilepsy. Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster) EEG Slide 05F.6 EEG and Sleep The electroencephalographic changes that occur as a human subject goes to sleep Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster) EEG Slide 05F.7 Questions Why are EEG signals on the surface of the scalp so small? Why are the brain neuronal signals obtained with needle electrodes so much larger? How accurately is it possible to know the thoughts in the brain from the EEG signals? The ECG is described as a vector field? Why not the EEG? What is the frequency content of EEG signals? Is this lower of higher than ECG / EMG? Why do EEG signals not appear to be stochastic noise like EMG signals? Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster)