Similarities in precursory features in seismic shocks and epileptic seizures

– Theoretical studies suggest that the final earthquake (EQ) and neural-seizure dynamics should have many similar features and could be analyzed within similar mathematical frameworks. Herein, by monitoring the temporal evolution of the fractal spectral characteristics in EEG time series and pre-seismic electromagnetic (EM) time series we show that many similar distinctive symptoms (including common alterations in associated scaling parameters) emerge as epileptic seizures (ES) and EQs are approaching. These alterations reveal a gradual reduction of complexity as the catastrophic events approach. The transition from anti-persistent to persistent behaviour may indicate that the onset of a severe crisis is imminent. The observations find a unifying explanation within the school of the “Intermittent Criticality”. Introduction. – Both EQ and ES involve interacting threshold elements. A large event, i.e. a seismic shock or an epileptic seizure, is the result of repeated nonlinear interactions among the respective sub-units, namely, opening cracks (that emit EM emission) or firing neurons. A common hallmark of these out-of-equilibrium phenomena is their extraordinary complexity. Complex systems self-organise their internal structure and their dynamics showing novel and surprising macroscopic properties including coherent large-scale collective behaviours. A basic reason for our interest in complexity is the striking similarity in behaviour close to irreversible phase transitions among systems that are otherwise quite different in nature [1–3]. Recent studies have demonstrated that a large variety of complex processes, including EQs [4, 5], forest fires [6], heartbeats [7], human coordination [8], neuronal dynamics [9–11], exhibits statistical similarities, most commonly the power law scaling behaviour of a particular observable. The strong analogies between the dynamics of the “self-organized– criticality” (SOC) model for EQs and that of neurobiology have been realized by numerous of authors, e.g. [12–15]. Interestingly, authors have suggested that EQ dynamics and neurodynamics should have many similar features and could be analyzed within similar mathematical frameworks [9–11]. Here, we attempt to verify this hypothesis.