, 1993b). This suggests that arousal influences local cortical networks find more via long-range afferent synaptic inputs and may differentially affect thalamorecipient and nonthalamorecipient layers. Other studies have, however, shown that stimulation of the basal forebrain, the cortical source of cholinergic innervation, also produces awake-like cortical activity in anesthetized animals (Goard and Dan, 2009, Metherate et al., 1992, Steriade et al., 1993a and Steriade et al., 1993b). We therefore

sought (1) to characterize the impact of arousal on neurons in each cortical layer and (2) to determine the underlying mechanism in awake animals. We made whole-cell recordings from the same cortical neurons under both anesthesia and subsequent wakefulness. Wakefulness transformed the pattern of background synaptic inputs in every cell examined. Surprisingly, this transformation INCB018424 research buy was not mediated by long-range

afferent synapses or cholinergic modulation but rather by direct noradrenergic modulation of local cortical circuits. We conclude that arousal-related brain states force cortical networks into different processing regimes via the locus coeruleus-noradrenergic system. In head-fixed rats, we made whole-cell recordings from 105 neurons in layers 2–6 (L2–6) of rat barrel cortex. Slow-wave fluctuations were prominent in a representative L2/3 pyramidal neuron during administration of gaseous isoflurane anesthesia (Figure 1A, upper). In the same cell, prolonged periods of synaptic quiescence disappeared during wakefulness, which was defined by overt jaw/face/whisker/paw movements and desynchronized EEG following termination of gas flow (middle; Movie S1, available online). Pronounced slow-wave fluctuations were restored when the animal was reanesthetized (lower),

confirming that the effect of wakefulness on Vm was not artifact due to rupturing of the cell membrane by animal movement. To quantify Vm changes, we algorithmically detected periods of synaptic quiescence (Figure S1A). Sustained synaptic quiescence decreased after the anesthetic was switched off (Figure 1B). This coordinated synaptic inactivity virtually disappeared before the animal awoke and remained Urease absent until the anesthetic resumed. We analyzed 52 anatomically identified cortical neurons (nine to 13 in each layer; three smooth inhibitory and 49 spiny excitatory cells). Recordings were maintained during anesthetized, awake, and reanesthetized phases. In every cell examined, wakefulness dramatically reduced mean quiescent periods (Figure 1C). Our algorithm is generous, classifying some epochs with minimal synaptic input as periods of quiescence (Figure S1B). Including such false positives, nominal periods of quiescence accounted for only 1.1% ± 0.5% of the awake period (mean ± standard deviation [SD]). Thus, wakefulness lacks periods during which the entire cortical network is inactive.