Complexity and schizophrenia

Abstract

Complexity estimators have been broadly utilized in schizophrenia investigation. Early studies reported increased complexity in schizophrenia patients, associated with a higher variability or "irregularity" of their brain signals. However, further investigations showed reduced complexities, thus introducing a clear divergence. Nowadays, both increased and reduced complexity values are reported. The explanation of such divergence is a critical issue to understand the role of complexity measures in schizophrenia research. Considering previous arguments a complementary hypothesis is advanced: if the increased irregularity of schizophrenia patients' neurophysiological activity is assumed, a "natural" tendency to increased complexity in EEG and MEG scans should be expected, probably reflecting an abnormal neuronal firing pattern in some critical regions such as the frontal lobes. This "natural" tendency to increased complexity might be modulated by the interaction of three main factors: medication effects, symptomatology, and age effects. Therefore, young, medication-naïve, and highly symptomatic (positive symptoms) patients are expected to exhibit increased complexities. More importantly, the investigation of these interacting factors by means of complexity estimators might help to elucidate some of the neuropathological processes involved in schizophrenia.

Keywords: AMI; Age; ApEn; CMI; CN; CPT; Complexity; CΩ; D2; EEG; FD; HFD; Higuchi's fractal dimension; L1; LZC; Lempel-Ziv complexity; MEG; MI; MSE; Negative symptoms; Neuroleptics; Positive symptoms; SampEn; Schizophrenia; approximate entropy; auto mutual information; continuous performance test; correlation dimension; cross mutual information; electroencephalography; first Lyapunov exponent; fractal dimension; magnetoencephalography; multiscale entropy; mutual information; neural complexity; omega complexity; sample entropy..