Atormac
brintellex
Neurology India
menu-bar5 Open access journal indexed with Index Medicus
  Users online: 2600  
 Home | Login 
About Editorial board Articlesmenu-bullet NSI Publicationsmenu-bullet Search Instructions Online Submission Subscribe Videos Etcetera Contact
  Navigate Here 
 Search
 
  » Next article
  » Previous article 
  » Table of Contents
  
 Resource Links
  »  Similar in PUBMED
 »  Search Pubmed for
 »  Search in Google Scholar for
 »Related articles
  »  Article in PDF (142 KB)
  »  Citation Manager
  »  Access Statistics
  »  Reader Comments
  »  Email Alert *
  »  Add to My List *
* Registration required (free)  


  In this Article
 »  Abstract
 »  Introduction
 »  Material and methods
 »  Results
 »  Discussion
 »  References

 Article Access Statistics
    Viewed6274    
    Printed112    
    Emailed1    
    PDF Downloaded135    
    Comments [Add]    
    Cited by others 2    

Recommend this journal

   
Year : 2002  |  Volume : 50  |  Issue : 2  |  Page : 181-3

Surface mapping of spike potential fields : visual vs. quantitative EEG analysis.


Department of Neurology, Nizam's Institute of Medical Sciences, Panjagutta, Hyderabad, 500034, India.

Correspondence Address:
Department of Neurology, Nizam's Institute of Medical Sciences, Panjagutta, Hyderabad, 500034, India.

  »  Abstract

Interictal EEG spike field potentials by visual and quantitative EEG analysis were studied in 17 patients with intractable localization related epilepsy. Quantitative EEG analysis was done using commercially available window based computer program (Focus) that displayed digitally acquired EEG data and performed spline mapping. Routine EEG localized 20 spikes. Fourteen spikes had excellent congruence between manual and computer generated mapping, 6 had good congruence, and 1 had fair congruence. This study clearly proves the usefulness of spline interpolation mapping technique in localizing and characterizing the epileptiform focus.

How to cite this article:
Prasad V S, Murthy J M, Sailaja S. Surface mapping of spike potential fields : visual vs. quantitative EEG analysis. Neurol India 2002;50:181


How to cite this URL:
Prasad V S, Murthy J M, Sailaja S. Surface mapping of spike potential fields : visual vs. quantitative EEG analysis. Neurol India [serial online] 2002 [cited 2020 Nov 28];50:181. Available from: https://www.neurologyindia.com/text.asp?2002/50/2/181/1399




   »   Introduction Top

Spatiotemporal source analysis provides a tool for identifying brain regions which are active and contribute to the epileptiform discharges recorded from the scalp signals.[1-6] Source waveforms proved particularly useful for revealing deep, tangentially oriented source currents. It is virtually impossible to detect these deep currents as these are widespread at the scalp and much weaker in amplitude as compared to the over lapping radial activities of the superficial cortex.[3],[7] Spatio-temporal source analysis also greatly improves interpretation of scalp EEG.[7],[8] Kozser et al[8] have shown that the dynamics of spike activity, including correlations, are better visualized using the computerized technique than by manual interpretation alone. In this study, spike fields were studied using commercially available computer based program in patients with medically intractable localization related epilepsy.


   »   Material and methods Top

Continuous long-term EEG monitoring was performed on 17 patients with medically intractable localization-related epilepsy, using a 32 channels Neurofax EEG 2100 recording system (Nihon Kohden Corporation). Data was stored in a digital format at 200 samples/sec using an ear reference. A high pass filter of 1.6 Hz with a roll-off response of 6 dB octave
was used in all analyses. A low pass filter of 35 or 7Hz was used as needed to minimize artifacts. 'Focus' program was used for spline and voltage mapping. This window based computer program displayed digitally acquired EEG data and performed spline mapping. The point in time that was of interest was chosen to display voltage mapping. The spike field analysis was done visually by two electroencephalographers using information from 5 standard montages (longitudinal, bipolar, transverse, ear references, vertex reference and average reference). Surface negativity or positivity were selected to analyze maximum amplitude of spikes.[9] Spline voltage maps were also produced by spherical spline interpolation at these same points in time using data from 23 electrodes. The congruence of the electroencephalographers maps to the computer maps was determined using the criteria proposed by Kozser et al[8] [Table I].



   »   Results Top

Routine EEG localized twenty spiked form 17 patients. Eleven patients had temporal spikes, 4 had frontal spikes and 2 had parietal spikes. In 18 spikes the highest voltage was surface negative and in 2 spikes it was surface positive [Table I]. Fourteen spikes had excellent congruence between manual and computer generated mapping [Figure - 1], 6 had good congruence [Figure - 2] and 1 fair congruence. Of the 11 temporal spikes, 10 showed large temporal negativity, rapid fall-off and contralateral positivity parasagitally and one had temporal negativity, a more gradual fall
and no contralateral positivity. Study of dynamic changes in the spike time showed surface positivity of early portion of these spikes which later evolved over 55-60 ms to large surface negativity in the same location.


   »   Discussion Top

Spline interpolation is the best algorithm for voltage mapping of spike potential fields.[10-12] The imaging of source activity waveforms by the spline interpolation method can be readily applied in parallel to traditional bipolar and referential montages. Kozser et al[8] have shown that EEG localization using spline mapping offers results comparable to traditional EEG interpretation. All spikes analyzed had excellent or
good congruence between the two methods. Ebersole and Wade[13] described two distinctive temporal spike populations in patients with complex partial epilepsy. Type I spike had a large temporal negativity, rapid fall-off and the existence of contralateral positivity parasagittally. These spikes are associated with mesial temporal sclerosis and outcome in these patients is excellent. Computerized spline mapping provides a means to examine the voltage fields of small and often overlooked early positivity of biphasic waves.[8] The
dynamic changes in these epileptiform potential have experimental physiologic correlates. Recordings in the experimental model showed biphasic paroxysmal activity close to the focus that began with a small early positivity followed by a large negativity.[14] This study clearly shows usefulness of spline interpolation mapping technique in localizing and characterizing the epileptiform focus.

 

  »   References Top

1.Scherg M : Functional imaging and localization of electromagnetic brain activity. Brain Topogr 1992; 5 : 103111.   Back to cited text no. 1    
2.Baumgartner C, Suthering WW, Shi DI et al : Investigation of multiple simultaneously active brain sources in the electroencephalogram. J Neurosci Methods1989; 30 : 175-184.   Back to cited text no. 2    
3.Ebersole JS : EEG dipole modeling in complex partial epilepsy. Brain Topogr1991; 4 : 113-123.   Back to cited text no. 3    
4.Scherg M, Ebersole JS : Models of brain sources. Brain Topogr1993; 5 : 419-423.   Back to cited text no. 4    
5.Scherg M : From EEG source localization to source imaging. Acta Neurol Scand1994; 152 : 29-30.   Back to cited text no. 5    
6.Scherg M, von Cramon D : Two bilateral sources of the late AEP as identified by a spatio-temporal dipole model. Electroencephalogr Clin Neurophysiol1985; 62 : 32-44.   Back to cited text no. 6    
7.Scherg M, Ebersole JS : Brain source imaging of focal and multi focal epileptiform EEG activity. Neurophysiol Clin 1994; 24 : 51-60.   Back to cited text no. 7    
8.Kozser S, Moshe SL, Legatt AD et al : Surface mapping of spike potential fields: experienced EEGers vs. computerized analysis. Electroencephalogr Clin Neurophysiol 1996; 98 : 199-205.   Back to cited text no. 8    
9.Niedermeyer E : The EEG signal: polarity and field determination. In : Electroencephalography: basic principles, clinical applications and related fields, Niedermeyer E, Lopes da Silva F (eds). 2nd Edition. Urban and Schwarzenberg, Baltimore. 1987; 79-83.   Back to cited text no. 9    
10.Perrin F, Pernier J, Bertrand O et al : Spherical splines for scalp potential and current density mapping. Electroencephalogr Clin Neurophysiol1989; 72 : 184-187.   Back to cited text no. 10    
11.Soufflet L, Toussaint M, Luthringen R et al : A statistical evaluation of main interpolation methods applied to 3dimentional EEG mapping. Electroencephalogr Clin Neurophysiol 1991; 79 : 393-402.   Back to cited text no. 11    
12.Soong A, Lind JC, Shaw GR et al : Systemic comparisons of interpolation techniques in topographic brain mapping. Electroencephalogr Clin Neurophysiol 1993; 87 : 185-195.   Back to cited text no. 12    
13.Ebersole JS, Wade PB : Spike voltage topography and equivalent dipole localization in complex partial epilepsy. Brain Topogr1990; 3 : 21-34.   Back to cited text no. 13    
14.Goldensohn EJ, Zablow L, Salazar A : The penicillin focus. I. Distribution of potential at the cortical surface. Electroencephalogr Clin Neurophysiol 1991; 42 : 480-492.   Back to cited text no. 14    

 

Top
Print this article  Email this article
Previous article Next article
Online since 20th March '04
Published by Wolters Kluwer - Medknow