Recent findings in cognitive neuroscience indicate that activation of anterior cingulate cortex (ACC) is related to detecting cognitive conflict, dissociation and pain. Conflict related and pain experience induced ACC activation elicits responses in central autonomic network which can be assessed by psychophysiological measures such as heart rate variability (i.e. beat to beat R-R intervals- RRI). Recent findings in neuroscience also suggest that cognitive conflict is related to specific nonlinear chaotic changes of the signal generated by the neural systems.

The present study used Stroop word-colour test as an experimental approach to the study of cognitive conflict in connection with RRI measurement, psychometric measurement of dissociation (DES), somatoform dissociation (SDQ-20), and calculation of largest Lyapunov exponents in nonlinear data analysis of RRI time series in 45 patients with unipolar depression (i.e. depressive period or recurrent depression).

Significant correlation 0.57 (p<0.01) between largest Lyapunov exponents and DES, and 0.45 (p<0.01) between largest Lyapunov exponents and SDQ-20 found in this study indicate that cognitive conflict related defect of neural inhibition during conflicting Stroop task is closely related to dissociative processes and depression.

These findings suggest the hypothesis that specific nonlinear dynamics governs the brain processes that link psychological pain related to dissociation and somatoform dissociation related to painful physical symptoms as a consequence of ACC activation.