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Geodesic Sensor Net Technical Manual
S-MAN-200-GSNR-001 • January 31, 2007
PREFACE
he Geodesic Sensor Net (GSN) from Electrical
Geodesics, Inc. (EGI) is the first practical, safe method
for quickly placing 32 to 256 electrodes on the human head
to acquire dense-array electroencephalography (EEG)
data. Its rapid application and comfortable fit, as well as
the rich data it provides, make the GSN ideal for a wide
range of subjects/patients and applications.
The GSN features EGI’s patented dense-array EEG sensors
held in a tension structure that stretches over the head.
Each line between sensor pairs is a
geodesic
, the shortest
distance between two points on the surface of a sphere.
The accurate geodesic tesselation of the head surface
optimizes the sampling of the electrical field.
The geodesic tension network enables the placement of a
large number of electrodes on the scalp in a minimal
amount of time. The average application time for a 128-
channel GSN is 10 minutes, compared with the more than
two hours required by conventional EEG techniques. The
GSN’s high-impedance electrodes do not call for scalp
abrasion, thus increasing patient comfort and decreasing
infection risk.
EGI currently offers two versions of the Geodesic Sensor Net: the HydroCel GSN
(HCGSN) and GSN 200. This manual discusses the two models together because they
share many similarities. General information about their individual properties is
provided in Chapter 2, "HCGSN,” and Chapter 3, "GSN 200.” The models also have
different sensor layouts (see Appendix B, "Net Sizing and Sensor Layouts”) because
the HCGSN is designed to provide more coverage of lower sections of the head.
Consequently, EEG files acquired with the older GSN 200 are incompatible with those
acquired with the newer HCGSN.
T
The geodesic structure
allows for quick and
painless application.
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