Single-neuron dynamics in human focal epilepsy

Abstract

Epileptic seizures are traditionally characterized as the ultimate expression of monolithic, hypersynchronous neuronal activity arising from unbalanced runaway excitation. Here we report the first examination of spike train patterns in large ensembles of single neurons during seizures in persons with epilepsy. Contrary to the traditional view, neuronal spiking activity during seizure initiation and spread was highly heterogeneous, not hypersynchronous, suggesting complex interactions among different neuronal groups even at the spatial scale of small cortical patches. In contrast to earlier stages, seizure termination is a nearly homogenous phenomenon followed by an almost complete cessation of spiking across recorded neuronal ensembles. Notably, even neurons outside the region of seizure onset showed significant changes in activity minutes before the seizure. These findings suggest a revision of current thinking about seizure mechanisms and point to the possibility of seizure prevention based on spiking activity in neocortical neurons.

Autistic characteristics in adults with epilepsy

“…For the individual to successfully prevent a seizure, time may be needed to employ a defensive strategy. Recent research has identified significant changes in neuronal activation in areas remote to the focal seizure onset minutes before the seizure actually begins (Truccolo et al, 2011). This is consistent with Bertram's description of how seizures start with an assemblage of neurons across a circuit, in which the interactions determine if a seizure will occur.…”

Intracranial neuronal ensemble recordings and analysis in epilepsy

“…These units showed heterogeneous and complex behavior during interictal discharges than had been predicted from previous experimental settings. SUA activities during ictal events were also less hypersynchronous as was previously hypothesized (Babb et al, 1987;Truccolo et al, 2011). Detailed analysis of ictal unit firing revealed the presence of an inhibitory wave local to the seizure onset zone , suggesting that inhibitory input may prevent the spread of the seizure (Schevon et al, 2012).…”

“…On the other hand, this recording approach lacks laminar information and the sampled layer depends partly on the design of the probe. As for the Utah array, histology following resection confirmed the electrode tips to be located in the lower portion of layer III in 66% of recordings (Truccolo et al, 2011). However, due to incomplete penetration, the probe reached the cortical layers in a variable manner.…”

Initiation, Propagation, and Termination of Partial (Focal) Seizures

“…In this study of unit activity performed with tetrode electrodes, the decrease in firing gener- ated by principal neurons was preceded by an increase in the activity of units identified as inhibitory interneurons. A reduction of unit activity at seizure onset was seen also in multiunit studies performed during presurgical intracranial monitoring in drug-resistant patients with partial epilepsy (Truccolo et al 2011;Bower et al 2012;Schevon et al 2012), suggesting that dampening of neuronal firing at the very beginning of a partial seizure occurs in epileptic patients as well.…”