According to recent findings stress experiences represent significant condition in pathophysiology of depression and influence abnormal development in the brain. Repeated stress and cognitive conflict also may determine limbic irritability and temporal-limbic epileptic-like activity. Because recent findings indicate that epilepsy and epileptiform processes are related to increased neural chaos, in the distinct contrast to normal brain activity, aim of this study is to find relationship between neural chaos in autonomic responses reflecting brain activity during stress activation and limbic irritability.

For empirical examination of suggested hypothesis Stroop word-colour test, ECG recording, calculation of chaos indices i.e. largest Lyapunov exponents (LLEs) in nonlinear data analysis and psychometric measures of limbic irritability (LSCL-33) and depression (BDI-II) in 35 patients with unipolar depression and 35 healthy controls were used.

Significant correlation r=0.68 (p<0.01) between LLEs and LSCL-33 found in this study indicate that degree of chaos in autonomic responses during conflicting Stroop task reflected by LLEs is closely related to limbic irritability. Significant correlation r=0.47 (p<0.01) also has been found between LLEs and symptoms of depression assessed by BDI-II. In the control group similar correlations have not been found.

The results are in agreement with findings that epileptiform activity represents typical form of chaotic organization. Because limbic irritability is linked to seizure-like processes in the temporo-limbic structures, the correlation between LSCL-33 and LLEs might represent useful finding for understanding of neurobiological mechanisms underlying stress-related sensitization and could be useful for future research regarding anticonvulsant treatment of depression.