The Ictal Signature of Thalamus and Basal Ganglia in Focal Epilepsy

Abstract

ObjectiveTo determine the involvement of subcortical regions in human epilepsy by analyzing direct recordings from these regions during epileptic seizures using stereoelectroencephalography (SEEG).Methodswe studied the SEEG recordings of a large series of patients (74 patients, 157 seizures) with an electrode sampling the thalamus and in some cases also the basal ganglia (caudate nucleus −22 patients- and putamen—4 patients). We applied visual analysis and signal quantification methods (Epileptogenicity Index, EI) to their ictal recordings and compared electrophysiologic with clinical data.ResultsWe found that in 86% of patients thalamus was involved during seizures (visual analysis) and that 20% showed high values of epileptogenicity (EI >0.3). Basal ganglia may also disclose high values of epileptogenicity (9% in caudate nucleus) but to a lesser degree than thalamus (p < 0.01). We observed different seizure onset patterns including low voltage high frequency activities. We found high values of thalamic epileptogenicity in different epilepsy localisations, including opercular and motor epilepsies. We found no difference between epilepsy aetiologies (cryptogenic vs malformation of cortical development, p = 0.77). Thalamic epileptogenicity was correlated with the extension of epileptogenic networks (p = 0.03, ρ 0.32). We found a significant effect (p < 0.05) of thalamic epileptogenicity regarding the post-surgical outcome (higher thalamic EI corresponding to higher probability of surgical failure).ConclusionsThalamic involvement during seizures is common in different seizure types. The degree of thalamic epileptogenicity is a possible marker of the epileptogenic network extension and of post-surgical prognosis.

Cheers for SANTĖ: Long Term Safety and Efficacy of Anterior Nucleus of the Thalamus DBS

“…For instance, a recent study indicated that the medial pulvinar nucleus frequently participated in focal seizures, with early involvement in seizure generation, in a subset of patients with epileptogenic foci localized to different regions and of mixed etiologies. 11 Are there different thalamic nuclei that should be targeted depending on the epileptic syndrome, ie, localization-related vs symptomatic generalized epilepsy? Can the incidence of adverse effects on mood and cognition be minimized by differential stimulation paradigms/targets?…”

Ictal connectivity changes induced by pulvinar stimulation correlate with improvement of awareness

“…Thalamic stimulation was shown to be effective in reducing AOA [3]. The medial pulvinar (PuM) is a thalamic nucleus often involved in focal seizures in different type of epilepsy [4]. In a recent work [5], we observed that high frequency stimulation of the PuM during temporal lobe seizures could lead to improvement of awareness.…”

On seizure semiology

“…It is recognized that subcortical mechanisms must play a role in clinical expression of many forms of focal seizure 7,64–68 . Although subcortical structures are much less often sampled than cortical structures, growing interest has led to increasing EEG data in a clinical context from structures including the thalamus, putamen, and caudate nucleus 69,70 . SEEG studies of synchrony during seizures have confirmed a link between degree of thalamic involvement and degree of alteration of consciousness, for example (see Table 1).…”