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Keywords:

  • EEG-fMRI;
  • Absence epilepsy;
  • BOLD response;
  • Thalamus;
  • Cortical focus

Summary

Purpose: Absences are characterized by an abrupt onset and end of generalized 3–4 Hz spike and wave discharges (GSWs), accompanied by unresponsiveness. Although previous electroencephalography–functional magnetic resonance imaging (EEG–fMRI) studies showed that thalamus, default mode areas, and caudate nuclei are involved in absence seizures, the contribution of these regions throughout the ictal evolution of absences remains unclear. Furthermore, animal models provide evidence that absences are initiated by a cortical focus with a secondary involvement of the thalamus. The aim of this study was to investigate dynamic changes during absences.

Methods: Seventeen absences from nine patients with absence epilepsy and classical pattern of 3–4 Hz GSWs during EEG-fMRI recording were included in the study. The absences were studied in a sliding window analysis, providing a temporal sequence of blood oxygen–level dependent (BOLD) response maps.

Results: Thalamic activation was found in 16 absences (94%), deactivation in default mode areas in 15 (88%), deactivation of the caudate nuclei in 10 (59%), and cortical activation in patient-specific areas in 10 (59%) of the absences. Cortical activations and deactivations in default mode areas and caudate nucleus occurred significantly earlier than thalamic responses.

Discussion: Like a fingerprint, patient-specific BOLD signal changes were remarkably consistent in space and time across different absences of one patient but were quite different from patient to patient, despite having similar EEG pattern and clinical semiology. Early frontal activations could support the cortical focus theory, but with an addition: This early activation is patient specific.