Sharp-wave EEG abnormalities and neural complexity in depressive patients: preliminary report

Petr Bob

doi:10.1186/s40810-015-0011-y

Abstract

According to recent findings cognitive and emotional dysregulation in depression and psychiatric disorders may be related to deficits in inhibitory functions and temporo-limbic seizure-like activity due to specific changes in neural dynamics and complexity of neural networks. In order to evaluate the clinical utility of nonlinear analysis of EEG complexity (measured by Lyapunov exponents) and to assess underlying epileptiform changes, we studied a sample of 19 depressive patients including nine depressive patients with episodic sharp-wave EEG abnormalities and ten depressive patients without any abnormalities, and compared also subgroups of these patients who used benzodiazepine medication to assess its influence on EEG complexity. The results show that the depressive patients with episodic sharp-wave EEG abnormalities had significantly lower EEG complexity than the control groups of patients. The data also indicate that benzodiazepines significantly influence neural complexity and increase it in the subgroup of patients with sharp wave abnormalities, and on the other hand decrease the level of complexity in the control subgroup of depressive patients. In agreement with other findings results of this study suggest that sharp waves or other underlying epileptiform EEG abnormalities related to abnormal neural excitability and disturbances in brain inhibitory systems may be reflected in specific changes of EEG complexity. These specific changes in EEG complexity may be related to treatment resistance to usual medications in several depressive patients and might represent clinical indicators for anticonvulsant treatment.

Highlights

Cognitive and emotional dysregulation related to depression in many cases may be linked to abnormal neural excitability and deficits in inhibitory functions that may lead to temporo-limbic seizure-like activity which in certain neural mechanisms is similar to epilepsy (Post et al 1988; Roberts et al 1992)
In agreement with other findings results of this study suggest that sharp waves or other underlying epileptiform EEG abnormalities related to abnormal neural excitability and disturbances in brain inhibitory systems may be reflected in specific changes of EEG complexity
These specific changes in EEG complexity may be related to treatment resistance to usual medications in several depressive patients and might represent clinical indicators for anticonvulsant treatment

Summary

Introduction

Cognitive and emotional dysregulation related to depression in many cases may be linked to abnormal neural excitability and deficits in inhibitory functions that may lead to temporo-limbic seizure-like activity which in certain neural mechanisms is similar to epilepsy (Post et al 1988; Roberts et al 1992) These findings are in agreement with evidence of positive clinical response to anticonvulsant treatment in many psychiatric patients (Silberman et al 1985; Varney et al 1993; Johannessen 2008; Vigo & Baldessarini 2009; Kaufman 2011). Interesting new findings that could explain underlying dynamics of sensitization and kindling processes provide data about spatio-temporal structure of epileptiform neural dynamics that may be more regular with excessive order and lower neural complexity than normal, or more irregular, as uncorrelated randomness with higher complexity (Dawson 2004; Varela et al 2001; Stam 2005). According to recent findings cognitive and emotional dysregulation in depression and psychiatric disorders may be related to deficits in inhibitory functions and temporo-limbic seizure-like activity due to specific changes in neural dynamics and complexity of neural networks

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