Hadad, B. | bioRxiv Science

bioRxiv2025

Auditory network persistence of stimulus representation in awake and naturally sleeping mice

Persistent neural activity often outlasts sensory stimulation, bridging perception and action. While commonly linked to working memory and decision making, its existence during passive states and sleep remains unclear. Using chronic high-density electrophysiology in freely behaving mice, we show that population spiking activity across the auditory cortical hierarchy enables decoding of past stimuli long after their offset, during both wakefulness and sleep. Time-resolved decoding revealed that in wakefulness, persistent representations decay uniformly across sensory and association cortices, whereas during sleep, persistence is prolonged in association cortex but remains brief in early auditory regions. Recurrent neural network modeling showed that higher internal noise during wakefulness reproduces this pattern, suggesting that reduced interference during sleep stabilizes sensory traces in associative areas. Our results demonstrate that persistent representation is a passive, state-dependent feature of sensory processing, supporting sensory maintenance even in the absence of active engagement.

neuroscience↗

bioRxiv2024

Changes in responses of auditory cortex neurons upon falling asleep and awakening

The neural processes that change when falling asleep are only partially understood. At the cortical level, features of both spontaneous neural activity and sensory responses change between wakefulness and sleep. For example, in early auditory cortex, sleep increases the occurrence of post-onset silent (OFF) periods and elevates population synchrony. However, it remains unknown whether such changes occur abruptly or gradually around sleep onset and awakening. Here, we recorded spontaneous and sound-evoked neuronal spiking activity in early auditory cortex along with polysomnography during thousands of episodes when male rats fell asleep or woke up. We found that when falling asleep, stimulus-induced neuronal silent periods (OFF periods), characteristic of non-rapid eye movement (NREM) sleep, increased within few seconds around sleep onset. By contrast, a gradual increase in neuronal population synchrony built up over tens of seconds until reaching maximal levels. EEG auditory-evoked potentials likely representing stimulus-triggered "K complexes" changed along with post-onset neuronal firing, whereas ongoing EEG slow wave activity was associated with neuronal population synchrony. Similar effects, but with opposite direction, were observed around awakenings. The results highlight late stimulus-induced neuronal silence as a key feature changing abruptly around transitions between vigilance states, likely reflecting neuronal bistability and manifesting also in EEG evoked potentials. More generally, these findings emphasize the added value of going beyond monitoring ongoing activity and perturbing the nervous system to reveal its state - an insight that could also help guide development of more sensitive non-invasive monitors of falling asleep in humans.

neuroscience↗