Sleep oscillations developing into seizures in corticothalamic systems

Area of Science:

• Neuroscience
• Epileptology
• Sleep Medicine

Background:

• Sleep oscillations play a critical role in various neurological functions and disorders.
• Understanding the neuronal basis of seizure generation is crucial for developing effective treatments.

Purpose of the Study:

• To investigate the neuronal substrates of sleep oscillations that lead to spike-wave (SW) and polyspike-wave (PSW) seizures.
• To differentiate the mechanisms underlying absence epilepsy-like SW seizures and Lennox-Gastaut syndrome (LGS)-associated PSW seizures.

Main Methods:

• Extracellular recordings were performed in cats during natural sleep-wake cycles.
• Simultaneous recordings were conducted from cortical and thalamic neurons, as well as cortical neurons and glial cells.
• Experiments included naturally sleeping animals and thalamectomized preparations.

Main Results:

• Spike-wave (SW) seizures can originate in the neocortex, even in the absence of thalamic input (thalamectomized animals).
• In intact brains, SW seizures initiate in the neocortex and spread to the thalamus.
• Thalamocortical (TC) neurons are predominantly hyperpolarized during SW seizures and show disinhibition post-seizure.
• Lennox-Gastaut syndrome (LGS) seizures involve complex neuronal dynamics, including inhibitory components and disfacilitation.

Conclusions:

• Seizures with SW complexes and LGS-type seizures preferentially emerge from sleep oscillations.
• These seizure types initiate in the neocortex and subsequently involve the thalamus.
• Thalamocortical neurons are largely inhibited during the progression of these seizures.