CORTICOTHALAMIC DIALOGUE IN STATES OF VIGILANCE AND SEIZURES

The concept that guides our experiments is as follows: the cerebral cortex and the thalamus constitute a unified neuronal network and any attempt towards the understanding of rhythmic cerebral activities during different behavioral states requires intact-brain preparations.

We have been investigating spontaneously occurring brain oscillations and fluctuations in the excitability of cortical and thalamic neurons during states of vigilance, as well as the transition from normally synchronized states (such as resting sleep) to epileptic-like paroxysmal events. These studies aim at revealing the neuronal processes underlying the phenomena generated in the corticothalamic networks, such as wake and sleep states, short-term plasticity following protracted rhythmic activity, and some types of epileptic seizures that preferentially occur during sleep.

For these studies, we are using three experimental models.

1. The disclosure of fine neuronal events requires intracellular recordings in animal experiments. At this time, our laboratory is the only one able to perform dual simultaneous intracellular recordings in vivo, in the cortex and the thalamus. This is necessary for the understanding of neuronal synchronization in corticothalamic networks and disclose complex temporal relations between cortical and thalamic neurons (see figure). We are now preparing to use triple intracellular recordings. The input-output organization of recorded neurons is identified by electrophysiological procedures. Neuron morphology as well as their precise locations are determined by intracellular staining with different dyes.

2. As intracellular recording can only be studied under anesthesia (because of stability problems), we validate these data in chronically implanted, behaving animals, using multi-site extracellular recordings of single units and field potentials.

3. In problems regarding states of vigilance, we also analyze EEG data recorded during the natural sleep cycle in humans.

These projects are supported by the Medical Research Council of Canada, the Natural Sciences and Engineering Research Council of Canada, the Human Frontier Science Program and the Savoy Foundation.

Steriade M, Jones EG, McCormick DA (1997) Thalamus. vol.1-2, 1738. Oxford Elsevier.