RT Book, Section
A1 Aminoff, Michael J.
A2 Hauser, Stephen L.
A2 Josephson, S. Andrew
SR Print(0)
ID 1145767470
T1 ELECTRODIAGNOSTIC STUDIES OF NERVOUS SYSTEM DISORDERS: EEG, EVOKED POTENTIALS, AND EMG
T2 Harrison's Neurology in Clinical Medicine, 4e
YR 2018
FD 2018
PB McGraw-Hill Education
PP New York, NY
SN 9781259835865
LK neurology.mhmedical.com/content.aspx?aid=1145767470
RD 2024/04/20
AB The  electrical  activity  of  the  brain  (the  electroencephalogram  [EEG])  is  easily  recorded  from  electrodes  placed  on  the  scalp.  The  potential  difference  between  pairs  of  electrodes  on  the  scalp  (bipolar  derivation)  or  between  individual  scalp  electrodes  and  a  relatively  inactive  common  reference  point  (referential  derivation)  is  amplified  and  displayed  on  a  computer  monitor,  oscilloscope,  or  paper.  Digital  systems  allow  the  EEG  to  be  reconstructed  and  displayed  with  any  desired  format  and  to  be  manipulated  for  more  detailed  analysis  and  also  permit  computerized  techniques  to  be  used  to  detect  certain  abnormalities.  The  characteristics  of  the  normal  EEG  depend  on  the  patient’s  age  and  level  of  arousal.  The  rhythmic  activity  normally  recorded  represents  the  postsynaptic  potentials  of  vertically  oriented  pyramidal  cells  of  the  cerebral  cortex  and  is  characterized  by  its  frequency.  In  normal  awake  adults  lying  quietly  with  the  eyes  closed,  an  8-  to  13-Hz  alpha  rhythm  is  seen  posteriorly  in  the  EEG,  intermixed  with  a  variable  amount  of  generalized  faster  (beta)  activity  (>13  Hz);  the  alpha  rhythm  is  attenuated  when  the  eyes  are  opened  (Fig.  6-1).  During  drowsiness,  the  alpha  rhythm  is  also  attenuated;  with  light  sleep,  slower  activity  in  the  theta  (4–7  Hz)  and  delta  (<4  Hz)  ranges  becomes  more  conspicuous.