The existence of low-dimensional deterministic structures in experimen
tal time series, derived from the occurrences of spikes in electrophys
iological recordings from rat brains, has been revealed in 7 out of 27
samples. The correlation dimension of the chaotic attractors ranged b
etween 0.14 and 3.3 embedded in a space of dimension 2-6. A test on su
rrogate data was also performed.