Network persistent activity in the neocortex

During sleep and anesthesia the neocortex develops slow oscillations composed of alternating Up and Down states. Up states are short epochs of persistent activity reminiscent of the activated neocortex during arousal and cognition. Although it is well established that Up states are generated within the cortex from the synaptic interaction of a network of cells, it is not known how intrinsic (thalamocortical) and extrinsic (intracortical) inputs of the cortex may affect Up states. Also, the effect of Up states on cortical synapses is largely unknown and controversial. Using thalamocortical slices we set out to test both of these questions. We found that extrinsic and intrinsic cortical inputs differentially regulate persistent activity. Thalamocortical activity facilitates cortical Up states, while intracortical activity suppress them. Moreover, Up states differently affect thalamocortical and intracortical responses. Up states enhance thalamocortical responses while they dampen intracortical interactions. These results indicate that during Up states thalamocortical transmission is enhanced, while during Down states the induction of Up states by thalamocortical activity is facilitated. We propose that these effects serve to adjust the information processing state of the neocortex during behavior.