DIFFERENTIATION OF ALPHA-COMA FROM AWAKE-ALPHA BY NONLINEAR DYNAMICS OF ELECTROENCEPHALOGRAPHY

The electroencephalogram, as a probe of scalp-recorded electrical acti vity arising from the human cortex, provides useful information becaus e of its temporal and spatial organization. Recent developments in non linear dynamics suggest that an object can be constructed in an n-dime nsional space out of a temporal sequence of data such as an EEG signal and that its organization is characterized by the dimensionality of t he object (in this case, human brain activity). We have carried out an analysis of a set of alpha coma EEG patterns in comparison to the awa ke alpha EEG patterns of normal volunteers and patients. Alpha coma re corded from a single channel is visually indistinguishable from normal resting alpha due to its similar frequency spectrum (a broad-band spe ctrum with 1/f characteristics). Our results show that alpha coma dime nsionality, however, differs from that of normal alpha in that it has a greater variability over different temporal segments of EEG. Single channel recordings in 7 patients with alpha coma were differentiable f rom those of 10 subjects with ''normal'' EEGs. Through dynamic analysi s of the EEG, novel methods of signal extraction from EEG may become e vident and applicable to clinical practice.