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D03 In vivo activity of interneurons and principal cells in the epileptic medial temporal lobe in humans

Epileptic seizures are characterized by excessively synchronized neural activity that spreads over macroscopically extended brain regions. This abnormal synchronization is assumed to result from an abnormal interaction of principal cells, and the much smaller population of inhibitory interneurons. Inhibitory interneurons potently control the excitability and input-output properties of all principal glutamatergic neurons in the brain. In particular, the generation of an action potential in an inhibitory interneuron is capable of synchronously inhibiting large ensembles of principal neurons. Therefore, the timing of interneuron firing is of profound importance in the generation of different types of rhythmic activity in the normal brain. Indeed, in-vivo studies have found that different types of interneurons are exquisitely coordinated to the phasic ensemble activity. In epilepsy, disturbed function of inhibition, both with respect to the amount of inhibition and its timing have been described. However, the dynamics of inhibitory and excitatory neuron recruitment into ensemble activity in the human brain has not been studied. In this project we will take advantage of the unique possibility to record extracellularly from single neurons in the human medial temporal lobe (MTL) in-vivo to study the behavior of principal cells and interneurons during epileptic seizures and during cognitive processing.