Phase-locking of hippocampal interneurons' membrane potential to neocortical up-down states

During quiet wakefulness and sleep, and under anesthesia, the membrane potentials of neocortical pyramidal neurons show synchronous, slow oscillations, so-called up-down states ( UDS), that can be detected in the local field potential ( LFP). The influence of this synchronized, spontaneous neocortical activity on the hippocampus is largely unknown. We performed the first in vivo whole-cell recordings from hippocampal dorsal CA1 interneurons and found that their membrane potentials were phase-locked to neocortical up- down states with a small delay. These results provide strong evidence for cortico-hippocampal interaction and suggest that neocortical activity drives hippocampal interneurons during UDS.