ABSTRACT
Most evidence for chaos in the human central nervous system is based on the examination of single channel electroencephalogram's (EEG) by the Grassberger-Procaccia algorithm. Preliminary results of a study comparing EEGs against random-phase surrogates, undertaken in collaboration with James Theiler, have called previous results, indicating the presence of low-dimensional structure in the EEG into question. EEG records were obtained from normal adult subjects in three behavioral conditions: resting, performing mental arithmetic in steps of two, and performing mental arithmetic in steps of seven. In the recalculations, 220 EEG signals were examined. Six embeddings were constructed for each signal, and 39 random-phase surrogates were constructed for each signal. A total of 52,800 dimension estimates were thus obtained from the original EEGs and their surrogates. It seems clear that the case for chaos in the human central nervous system diminishes with each improvement in analytical technology.
