Objective: A chirp is a brief signal within which the frequency content cha
nges rapidly. Spectrographic chirps are found in signals produced from many
biological and physical phenomena. In radar and sonar engineering, signals
with chirps are used to localize direction and range to the signal source.
Although characteristic frequency changes during epileptic seizures have l
ong been observed, the correlation with chirps and chirp technology seems n
ever to have been made.
Methods: We analyzed 19 404 s (1870 a of which were from 43 seizures) of in
tracranially (subdural and depth electrode) recorded digital EEG from 6 pat
ients for the presence of spectral chirps. Matched filters were constructed
from methods in routine use in non-medical signal processing applications.
Results: We found that chirps are very sensitive detectors of seizures (83%
), and highly specific as markers (no false positive detections). The feasi
bility of using spectral chirps as matched filters was demonstrated.
Conclusions: Chirps are highly specific and sensitive spectrographic signat
ures of epileptic seizure activity. In addition, chirps may serve as templa
tes for matched filter design to detect seizures, and as such, can demonstr
ate localization and propagation of seizures from an epileptic focus. (C) 2
000 Elsevier Science Ireland Ltd. All rights reserved.