Modem findings in neuroscience suggest that cognitive conflict is related to specific nonlinear chaotic changes of the signál generated by neural systems. According to recent findings, activation of anterior cingulate cortex (ACC) is related to detecting cognitive conflict. This conflict-related activation elicits autonomie responses which can be assessed by psychophysiological measures such as heart rate variability calculated as beat to beat R-R intervals (RRI). The present study ušed Stroop test as an experimental approach to psychophysiological study of cognitive conflict in 40 patients with unipolar depression. In this experimental approach RRI measurement, psyhometric measurement of limbic irritability (LSCL-33), depression (BDI-II) and calculation of largest Lyapunov exponents in nonlinear data analysis of RRI time series were performed. Significant correlation coefficient of r=0.60 between largest Lyapunov exponents and LSCL-33 found in this study indicate that a defect of neural inhibition during conflicting Stroop task is closely related to limbic irritability. Since limbic irritability is probably closely related to epileptiform abnormalities in the temporo-limbic structures, this result might represent a useful instrument for indication of anticonvulsant treatment in depressive patients who are resistant to antidepressant medication.

        Key words: depression, stress, limbic irritability, HRV, Lyapunov exponent, chaos, anticonvulsants