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Related Experiment Videos

Negative BOLD responses to epileptic spikes.

Eliane Kobayashi1, Andrew P Bagshaw, Christophe Grova

  • 1Montreal Neurological Institute and Hospital, McGill University, Canada. eliane.kobayashi@mail.mcgill.ca

Human Brain Mapping
|September 24, 2005
PubMed
Summary

Deactivations in electroencephalogram/functional magnetic resonance imaging (EEG-fMRI) studies are common during epilepsy discharges. These deactivations, often linked to neuronal inhibition, can temporarily suspend normal brain function.

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Area of Science:

  • Neuroimaging
  • Epilepsy Research
  • Brain Activity Mapping

Background:

  • Simultaneous electroencephalogram/functional magnetic resonance imaging (EEG-fMRI) reveals both positive (activation) and negative (deactivation) blood oxygenation level-dependent (BOLD) signal changes during interictal epileptiform discharges.
  • While activation is linked to increased neuronal activity, the mechanisms behind deactivation remain less understood.

Purpose of the Study:

  • To investigate the occurrence and significance of deactivations associated with epileptiform discharges in epilepsy patients.
  • To correlate these deactivations with discharge type, location, and their relationship to the brain's resting state network.

Main Methods:

  • Reviewed EEG-fMRI studies, categorizing responses into activation, deactivation, or both.
  • Analyzed the spatial relationship of deactivations to discharge locations and default brain network regions.

Related Experiment Videos

  • Correlated findings with discharge characteristics like type (spike, polyspike, spike-and-slow wave) and laterality (focal, bilateral, generalized).

    • Main Results:

    • Deactivations were observed in 52 out of 60 studies, frequently accompanying activations.
    • Deactivations occurred with focal, bilateral, and generalized discharges, often distant from the discharge origin.
    • Spike-and-slow waves were more associated with deactivation than spikes alone.
    • The 'default' brain state network was involved in 10 studies, particularly with generalized discharges.

    Conclusions:

    • Deactivations are a frequent phenomenon during epileptiform discharges in epilepsy, often co-occurring with activations.
    • Neuronal inhibition is suggested as the mechanism underlying deactivations, especially those following slow waves.
    • The involvement of default network areas during generalized discharges indicates a subclinical disruption of normal resting-state brain function.