Pizarro, D. | Search bioRxiv

bioRxiv2020

Anterior Nucleus of Thalamus Gates Progression of Mesial Temporal Seizures by Modulating Thalamocortical Synchrony

The anterior nucleus of the thalamus (ANT) mediates cortical-subcortical interactions between the limbic system and is hypothesized to facilitate the early organization of temporal lobe seizures. We set out to investigate the dynamic changes in synchronization parameters between the seizure onset zone (SOZ) and ANT during seizure stages (pre-onset to post-termination) in seven patients (n=26 seizures) with drug-resistant nonlesional temporal lobe epilepsy. Using local field potentials recorded directly from the limbic system and the ANT during stereoelectroencephalography, we confirm that the onset of mesial temporal lobe seizure is associated with increased thalamocortical network excitability and phase-amplitude coupling. The increase in thalamocortical phase synchronization preceded seizure onset, thereby suggesting that the early organization of temporal lobe seizures involves the integration of the ANT within the epileptic network. Towards seizure termination, there is a significant decrease in thalamic excitability, thalamocortical synchronization, and decoupling, thereby suggesting a breakdown in thalamocortical connectivity. A higher disease burden is significantly correlated with increased synchronization between the ANT and epileptic networks. Collectively, the results elucidate mechanistic insights and provide the temporal architecture of thalamocortical interactions that can be targeted in the rational designing of closed-loop seizure abortive interventions. HighlightsO_LIAnterior nucleus of thalamus is coactivated at the onset of temporal lobe seizures C_LIO_LIIncrease thalamocortical synchronization and excitability is observed at seizure onset C_LIO_LISeizure termination is characterized by a breakdown in thalamocortical connectivity C_LIO_LIIncreased seizure burden affects thalamocortical synchronization C_LI

neuroscience↗

bioRxiv2019

Ictal recruitment of anterior nucleus of thalamus in human focal epilepsy

The thalamic nuclei play diverse roles in the initiation, propagation, and termination of temporal lobe seizures. The role of the anterior nucleus of the thalamus (ANT) - a node that is integral to the limbic network is unclear. The objective of this study was to characterize temporal and - spectral patterns of ANT ictal recruitment in drug-resistant temporal lobe epilepsy (TLE). We hypothesized that seizures localized to the temporolimbic network are likely to recruit ANT, and the odds of recruitment were higher in seizures that had altered consciousness. Ten patients undergoing stereo-electroencephalography (SEEG) were recruited prospectively to record field potentials from the ANT. Using epileptogenicity index and line length, we computed the number of seizures that recruited the ANT (recruitment ratio), the recruitment latencies between the ANT and the epileptogenic zone (EZ), and latency of ANT recruitment to clinical manifestation for seventy-nine seizures. We observed that seizures localized to mesial temporal subregions (hippocampus, amygdala, anterior cingulate) have a higher predilection for ANT recruitment, and the recruitment was faster (ranged 5-12 secs) and preceded clinical onset for seizures that impaired consciousness. Seizures that recruited ANT lasted significantly longer (t=1.795, p=0.005). Recruitment latency was inversely correlated to seizure duration (r=-0.78, p=0.004). Electrical stimulation of the EZ induced seizures, in which early recruitment of ANT was confirmed. Stimulation of ANT did not induce a seizure. Finally, we tested the hypothesis that spectral and entropy-based features extracted from thalamic field potentials can distinguish its state of ictal recruitment from other interictal states (including awake, sleep). For this, we employed classification machine learning that discriminated thalamic ictal state from other interictal states with high accuracy (92.8%) and precision (93.1%). Among the features, the emergence of the theta rhythm (4-8 Hz) maximally discriminated the endogenous ictal state from other interictal states of vigilance. These results prompt a mechanistic role for the ANT in the early organization and sustaining of seizures, and the possibility to serve as a target for therapeutic closed-loop stimulation in TLE.

neuroscience↗