Joanna Szczotka

Probing mechanisms of consciousness is often inadvertently entangled with probing mechanisms of sensory connectedness. Experimental assays typically rely on detecting a behavioural response to a stimulus, a perceptual report, or an evoked potential, treating the ability to register the external world as a proxy for the presence of consciousness itself. Yet sensory connectedness and consciousness can vary orthogonally. A brain may lose access to the external world while preserving a rich conscious experience, as in ketamine anaesthesia, classic psychedelic states, and the vivid dreaming of REM sleep. Conversely, forms of blindsight and automatic behaviour show that environmental information can guide action even when conscious experience is absent. Disentangling this dissociation is essential: it lets us separate how the brain generates subjective experience, how it anchors that experience to the external world, and why these two capacities sometimes align and sometimes drift apart. While recent work has begun to clarify cellular and network mechanisms underlying shifts in the level of consciousness (such as cortical desynchronization, edge-of-chaos criticality, or apical-somatic coupling in layer 5 pyramidal neurons), these findings remain anchored to sensory responsiveness-based definitions of consciousness. They do not explain how sensory disconnection is implemented, nor why disconnected states can range from richly experiential (as in REM) to nearly experience-free (as in deep NREM). Sleep provides a uniquely powerful natural experiment for probing this dissociation: both REM and NREM suppress sensory connectedness, yet their phenomenology differs substantially. Because connectedness is held near zero in both NREM and REM, what distinguishes them approaches a correlate of consciousness distilled from sensory connectedness. To explore this, we leverage 211 acute Neuropixels insertions sampling 67 brain regions in vivo across wake, NREM, and REM sleep in mice. With millisecond precision single-unit recordings, Neuropixels technology lets us bypass the indirectness and low resolution of conventional neuroimaging and observe the brain at its native scale of individual action potentials—across cortical hierarchies, thalamus, hippocampus, basal ganglia, brainstem nuclei, and cerebellum, simultaneously. Throughout the sleep cycle, we deliver controlled visual, auditory, and somatosensory stimuli, enabling us to track how sensory signals propagate through thalamic relays, cortical layers, subcortical loops, and long-range association pathways with true single-spike resolution. We reconstruct and visualize this propagation in 3D across the 31,076 neurons in the mouse brain. Crucially, when a sensory stimulus induces an awakening, we also witness a rare transition in real time: the re-coupling of disconnected consciousness to the external world. Examining these awakenings lets us resolve, in the seconds to milliseconds preceding behavioral response, which sensory hierarchies re-engage—which areas regain pattern stability, which thalamic and brainstem nuclei resume responsiveness, and which propagation bottlenecks reopen. Such transitions serve as natural causal probes into the architecture that differentiates disconnected from connected consciousness. Lastly, our findings impose new empirical constraints on theories of consciousness and sensory gating, and showcase Neuropixels as a transformative tool for resolving long-standing conceptual puzzles.

PhD candidate in neuroscience at Center for Sleep and Consciousness (UW-Madison), currently working under supervision of Giulio Tononi and Chiara Cirelli.