LOW-DIMENSIONAL CHAOTIC ATTRACTORS IN THE RAT-BRAIN

The existence of chaotic attractors for discrete time series, derived from the occurrences of spikes during electrophysiological recordings, was investigated, The time series included between 800 and 5200 point s per analyzed record. The spike trains were recorded in the substanti a nigra pars reticulata (n = 13) and in the auditory thalamus (n = 14) . The experiments were performed on anesthetized rats during spontaneo us activity and during auditory stimulation. According to standard met hods of dynamical systems theory, an embedding space was constructed u sing delay coordinates. The embedding and correlation dimensions were computed by means of the correlation integrals. For 7 of 27 samples, a deterministic structure with a low embedding dimension (ranging betwe en 2 and 6) and a correlation dimension between 0.14 and 3.3 could be determined. Evidence was found that the sensory stimulation may affect the chaotic behavior, Single units recorded simultaneously from the s ame electrode tip may display different chaotic dynamics, even with a similar time-locked response to the stimulus onset.