Preictal short-term plasticity induced by intracerebral 1 Hz stimulation

Abstract

Short-term changes of intrinsic properties of neural networks play a critical role in brain dynamics. In that context, epilepsy is a typical pathology where the fast transition between interictal and ictal states is probably associated to intrinsic modifications of underlying networks. In this study, we focused on the correlates of plastic neural mechanisms in the intracerebral electroencephalogram (iEEG). Data were obtained during 1 Hz electrical stimulation in twenty patients suffering from temporal lobe epilepsy and implanted with intracerebral electrodes for clinical evaluation before resective surgery. First, we developed a procedure of analysis for localisation of the seizure onset zone based on brain excitability and plasticity defined as the average, and as the first-order (linear) modulation respectively, of the standard deviation of iEEG responses over stimulations. Our results suggest that the candidate epileptic focus is particularly prone to exhibiting short-term plasticity. Second, we used Dynamic Causal Modelling (DCM) to model explicitly short-term plasticity as a fast modulation of synaptic efficacies in either intrinsic or extrinsic connections to the focus. We found the two types of modulation both likely. Third, we used DCM to study the fast modulation of synaptic connectivity of long-range connections in neuronal networks restricted to the temporal lobe. Using DCM, we were able to estimate which structures expressed a strong modulatory input to the epileptic focus. Such early changes in interregional connectivity might be important for the initiation of electrically-induced seizures. They may also reflect some aspects of the pathogenesis of epilepsy in those patients.

Cortico-cortical evoked potentials for sites of early versus late seizure spread in stereoelectroencephalography

“…This takes advantage of the excellent temporal and spatial resolution of intracranial EEG. Our data represent the first direct comparison of CCEP responses between clinically-verified early and late sites of seizure propagation; this extends theoretical work suggesting the seizure networks exhibit dynamic changes during ictal spread David et al (2008). sEEG differs significantly from standard subdural grid implantation in terms of the analysis of CCEP data.…”

Dynamic causal modeling of cortical activity from the acute to the chronic stage after stroke

“…However, some biophysiological and neurovascular processes are neglected in the current DCM implementation, probably because they may not be easily identified from fMRI data . Nevertheless, DCM has been validated by simulation and experimental studies in humans and animals (David et al, 2008a(David et al, , 2008bMoran et al, 2008). Importantly, the studies of David et al (2008ab) provide evidence for the validity of DCM for inferring network structure from fMRI data using simultaneous fMRI and electroencephalography (EEG) measurements in rodents with epileptic seizures.…”

On the modelling of seizure dynamics

“…Bayesian model comparison suggested that seizure onset could be modelled in terms of changes in intrinsic connectivity (as opposed to extrinsic connectivity). Furthermore, DCM identified fluctuations in synaptic efficacy in the ictal zone; suggesting that the mesial temporal lobe epilepsy studied by David et al (2008) could be explained in terms of a pre-ictal increase in sensitivity to hippocampal afferents from the temporal pole.…”

“…For example, David et al (2008) analysed seizure activity elicited during electrical stimulation. Bayesian model comparison suggested that seizure onset could be modelled in terms of changes in intrinsic connectivity (as opposed to extrinsic connectivity).…”