Turning off cortical ensembles stops striatal Up states and elicits phase perturbations in cortical and striatal slow oscillations in rat in vivo

In vivo, cortical neurons and striatal medium spiny neurons (MSN) display robust subthreshold depolarizations (Up states) during which they are enabled to fire action potentials. In the cortex, Up states are believed to occur simultaneously in a neuronal ensemble and to be sustained by local network interactions. It is known that MSN are impelled into the Up state by extra-striatal (primarily cortical) inputs, but the mechanisms that sustain and determine the end of striatal Up states are still debated. Furthermore, it has not been established if brisk perturbations of ongoing cortical oscillations alter rhythmic transitions between Up and Down states in striatal neurons. Here we report that MSN Up states terminate abruptly when persistent activity in cortical ensembles providing afferents to a given striatal region is turned off by local electrical stimulation or ends spontaneously. In addition, we found that phase perturbations in MSN membrane potential slow oscillations induced by cortical stimulation replicate the stimulus-induced dynamics of spiking activity in cortical ensembles. Overall, these results suggest that striatal Up states are single-cell subthreshold representations of episodes of persistent spiking in cortical ensembles. A precise spatial and temporal alignment between episodes of cortical persistent activity and striatal Up states would allow MSN to detect specific cortical inputs embedded within a more general cortical signal.