Neuronal dynamics in visual cortex under conscious and anesthetized conditions  Heonsoo Lee (Anesthesiology, University of Michigan, Ann Arbor, MICHIGAN Korea, Republic Of)   C20

Introduction: There has been an explosive proliferation of investigations using anesthetics as tools to probe neural activities associated with altered states of consciousness. Most studies focused on capturing large-scale neural events and their functional interactions measured with EEG or fMRI. However there has been relatively little focus on the difference of neuronal spike activities in waking and anesthetized conditions. In this study we explore how neuronal spike activities and their functional interactions alter under different levels of anesthesia. Methods: We measured single-unit activities in deep layers of primary visual cortex of adult rats under resting and repeated visual stimulation conditions. Anesthetic desflurane was administered at 6, 4, 2, and 0%. Results: Spontaneous spike activity in resting state under anesthesia was characterized by the following: (i) the number of actively firing neurons and overall firing rate decreased while the remaining active neurons showed increased burst-spiking ratio. (ii) correlation between neuron-to-population was profoundly increased while neuron-to-neuron information transfer decreased. (iii) although these changes became more pronounced as deepening of anesthesia, an intermittent, paradoxical period appeared at high-dose anesthesia, during which asynchronous firing patterns and high electromyographic activity were found. Contrary to evoked-potential studies under anesthesia, the flash-induced early response (spikes at 20-150ms post-stimulus) was attenuated, and their spike timing was split and delayed. Late response (spikes at 200-400ms post-stimulus) was also suppressed. Conclusions: The altered functional interactions of neuron-to-neuron and neuron-to-population suggest impaired information capacity under anesthesia. The finding of the paradoxical desynchronized brain state at high dose anesthesia challenges the assumption of monotonic, anesthetic dose-dependent behavior of cortical neuron populations.