Chaotic neural response during conflicting Stroop task reflects the level of serum cortisol in patients with unipolar depression.

OBJECTIVE: According to recent findings detecting a cognitive conflict is related to activation of anterior cingulate cortex (ACC) and central autonomic network. Several recent findings also suggest the hypothesis that the cognitive conflict is related to specific nonlinear chaotic changes of the neural signal. This conflict related activation elicits autonomic responses which can be assessed by psychophysiological measures such as heart rate variability calculated as beat to beat R-R intervals (RRI).

METHOD: The present study used Stroop word-colour test as an experimental approach to psychophysiological study of cognitive conflict in connection with RRI measurement, assessment of serum cortisol and calculation of largest Lyapunov exponents in nonlinear data analysis of RRI time series in 30 patients with unipolar depression.

RESULTS: Significant correlation -0.45 (p<0.01) between largest Lyapunov exponents during conflicting Stroop task and serum cortisol levels has been found.

CONCLUSIONS: The study indicates that a defect of neural inhibition during conflicting Stroop task is closely related to decreased serum cortisol levels which probably reflect defense psychological mechanisms.