Corticothalamic feedback can induce hypersynchronous low-frequency rhythmsin the physiologically intact thalamus

Thalamic circuits are capable of generating oscillations of different frequ ency and level of synchrony. However, it is not known how these oscillation types are controlled in the intact brain. Here we consider the influence o f corticothalamic feedback onto the thalamus by using thalamic slices and c omputational models. Models predicted that strong activation of corticothal amic feedback should transform the normal spindle oscillations (6-10 Hz) in to hypersynchronous slow (2-4 Hz) oscillations. By implementing this feedba ck paradigm in ferret thalamic slices, we could observe this transformation . Thalamic reticular neurons show a dramatic increase of firing, but not in terneurons, suggesting that this effect is mediated mostly through the reti cular nucleus. We conclude that cortical inputs can induce slow hypersynchr onous oscillations in the physiologically intact thalamus, which has clear implications for understanding the genesis of pathologies such as absence s eizures, and more generally the downstream control of thalamic nuclei by th e cerebral cortex. (C) 2001 Elsevier Science B.V. All rights reserved.