Consistent sequential activity across diverse forms of UP states under ketamine anesthesia

During slow‐wave sleep, the neocortex shows complex, self‐organized spontaneous activity. Similar slow‐wave oscillations are present under anesthesia where massive, persistent network activity (UP states) alternates with periods of generalized neural silence (DOWN states). To investigate the neuronal activity patterns occurring during UP states, we recorded simultaneously from populations of cells in neocortical layer V of ketamine/xylazine‐anesthetized rats. UP states formed a diverse class. In particular, simultaneous‐onset UP states were typically accompanied by sharp field potentials and 10–14 Hz modulation, and were often grouped in a 3 Hz (‘delta’) pattern. Longer, slow‐onset UP states did not exhibit 10–14 Hz modulation, and showed a slow propagation across recording electrodes (‘traveling waves’). Despite this diversity, the temporal patterns of spiking activity were similar across different UP state types. Analysis of cross‐correlograms revealed conserved temporal relationships among neurons, with each neuron having specific timing during UP states. As a group, putative interneurons were most active at the beginning of UP states and putative pyramidal cells were active uniformly throughout the duration of UP states. These results show that UP states under ketamine anesthesia have a stable, fine‐structured firing pattern despite a large variability in global structure.