EEG topographical analysis of spatial disorientation.
BACKGROUND
We examined EEG topography while subjects experienced spatial disorientation (SD) such as vection and somatogravic illusion (SGI).


METHODS
Five healthy male subjects were exposed to a rotating image evoking vection (Experiment 1) and to a 0.58 G linear forward acceleration evoking SGI (Experiment 2). The data were analog-to-digital converted with an epoch length of 1 s and a sampling frequency of 256 Hz. Polynomial coefficient vectors were calculated for the following analyses of EEG under the illusion: a) objective evaluation of topographical difference by two-way MANOVA; b) visual inspection of the power spectra maps; and c) logarithmic deviation ratio topography (log DRT).


RESULTS
MANOVA demonstrated significant differences in EEG topography in the high alpha band while the vection was evoked. No significant difference was revealed in any bands for SGI. Characteristic patterns common to all subjects were hardly identified on the power spectra maps. By log DRT under vection, a decrease of power was observed in the centro-parietal area on the left side in one subject, on the right in another subject, and in the mid-right frontal area in a third subject compared with the control with eyes open. As for SGI, log DRT revealed a decrease of power in the occipital area in most of the trials as the magnitude was reduced by a visible horizon.


CONCLUSIONS
MANOVA revealed a significant change in EEG topography while the subjects felt vection. Log DRT reflected characteristic patterns under vection and SGI. Thus EEG topography may be useful for the study of SD.
Tokumaru
O
O
Department of Physiology II, National Defense Medical College, Tokorozawa, Saitama, Japan.
Kaida
K
K
Ashida
H
H
Yoneda
I
I
Tatsuno
J
J
D000054:Acceleration; D000060:Accidents, Aviation; D000328:Adult; D000337:Aerospace Medicine; D001931:Brain Mapping; D004569:Electroencephalography; D006801:Humans; D007088:Illusions; D008297:Male; D009949:Orientation; D012399:Rotation; D012678:Sensation Disorders / Q000503:physiopathology*; D013028:Space Perception