Impaired top-down auditory processing despite extensive single-neuron responses during human sleep
Sleep in all species is universally defined as a reversible, homeostatically-regulated state of a reduced behavioral responsiveness, with a high arousal threshold in response to external sensory stimulation1. However, it remains unclear whether sleep mainly gates motor output or affects responses along sensory pathways, and whether sleep primarily modulates specific aspects of the sensory response such as feedforward vs. feedback signaling2-7. Here, we simultaneously recorded polysomnography, iEEG, microwire LFPs, and neuronal spiking activity during wakefulness and sleep in 13 epilepsy patients implanted with clinical depth electrodes, while presenting auditory stimuli (e.g. click-trains, words, music). The results revealed robust spiking and induced LFP high-gamma (80-200Hz) power responses during both NREM and REM sleep across the lateral temporal lobe. The magnitude of the responses was only moderately attenuated in sleep, most notably for late responses beyond the early auditory cortex. Nonetheless, sleep responses maintained their tight locking with soundwave envelopes and their information content was only minimally affected. In contrast, a decrease in LFP alpha-beta (10-30Hz) power responses was prevalent in wakefulness but significantly disrupted in sleep. Entrainment to 40 Hz click-trains was comparable across REM sleep and wakefulness, but reduced in NREM sleep. In conclusion, our results establish the presence of extensive and robust auditory responses during sleep while LFP alpha-beta power decrease, likely reflecting top-down processes8-10, is deficient. More broadly, our findings suggest that feedback signalling is key to conscious sensory processing11-13.