Differential cortical network engagement during states of un/consciousness in humans

Zelmann, R., Paulk, A., et al. (2023).

Neuron. Volume 111, (21)

https://doi.org/10.1016/j.neuron.2023.08.007

Summary

What happens in the human brain when we are unconscious? Despite substantial work, we are still unsure which brain regions are involved and how they are impacted when consciousness is disrupted. Using intracranial recordings and direct electrical stimulation, we mapped global, network, and regional involvement during wake vs. arousable unconsciousness (sleep) vs. non-arousable unconsciousness (propofol-induced general anesthesia). Information integration and complex processing we`re reduced, while variability increased in any type of unconscious state. These changes were more pronounced during anesthesia than sleep and involved different cortical engagement. During sleep, changes were mostly uniformly distributed across the brain, whereas during anesthesia, the prefrontal cortex was the most disrupted, suggesting that the lack of arousability during anesthesia results not from just altered overall physiology but from a disconnection between the prefrontal and other brain areas. These findings provide direct evidence for different neural dynamics during loss of consciousness compared with loss of arousability.

Highlights

• Decreased complexity and connectivity, with increased variability when unconscious

• Changes were more pronounced during propofol-induced general anesthesia than sleep

• During sleep, changes were homogeneously distributed across the human brain

• During anesthesia, substantial prefrontal disconnection is related to lack of arousability

A pdf is here.

Here is my summary:

State-Dependent Cortical Network Engagement

The human brain undergoes significant changes in its functional organization during different states of consciousness, including wakefulness, sleep, and general anesthesia. This study investigated the neural underpinnings of these state-dependent changes by comparing cortical network engagement during wakefulness, sleep, and propofol-induced general anesthesia.

Prefrontal Cortex Disruption during Anesthesia

The findings revealed that loss of consciousness, whether due to sleep or anesthesia, resulted in reduced information integration and increased response variability compared to wakefulness. However, these changes were more pronounced during anesthesia than sleep. Notably, anesthesia was associated with a specific disruption of the prefrontal cortex (PFC), a brain region crucial for higher-order cognitive functions such as decision-making and self-awareness.

Implications for Understanding Consciousness

These findings suggest that the PFC plays a critical role in maintaining consciousness and that its disruption contributes to the loss of consciousness during anesthesia. The study also highlights the distinct neural mechanisms underlying sleep and anesthesia, suggesting that these states involve different modes of brain function.

Sleep loss leads to the withdrawal of human helping across individuals, groups, and large-scale societies

Ben Simon E, Vallat R, Rossi A, Walker MP (2022) 

PLoS Biol 20(8): e3001733.

https://doi.org/10.1371/journal.pbio.3001733

Abstract

Humans help each other. This fundamental feature of homo sapiens has been one of the most powerful forces sculpting the advent of modern civilizations. But what determines whether humans choose to help one another? Across 3 replicating studies, here, we demonstrate that sleep loss represents one previously unrecognized factor dictating whether humans choose to help each other, observed at 3 different scales (within individuals, across individuals, and across societies). First, at an individual level, 1 night of sleep loss triggers the withdrawal of help from one individual to another. Moreover, fMRI findings revealed that the withdrawal of human helping is associated with deactivation of key nodes within the social cognition brain network that facilitates prosociality. Second, at a group level, ecological night-to-night reductions in sleep across several nights predict corresponding next-day reductions in the choice to help others during day-to-day interactions. Third, at a large-scale national level, we demonstrate that 1 h of lost sleep opportunity, inflicted by the transition to Daylight Saving Time, reduces real-world altruistic helping through the act of donation giving, established through the analysis of over 3 million charitable donations. Therefore, inadequate sleep represents a significant influential force determining whether humans choose to help one another, observable across micro- and macroscopic levels of civilized interaction. The implications of this effect may be non-trivial when considering the essentiality of human helping in the maintenance of cooperative, civil society, combined with the reported decline in sufficient sleep in many first-world nations.

From the Discussion section

Taken together, findings across all 3 studies establish insufficient sleep (both quantity and quality) as a degrading force influencing whether or not humans wish to help each other, and do indeed, choose to help each other (through real-world altruistic acts), observable at 3 different societal scales: within individuals, across individuals, and at a nationwide level.

Study 1 established not only the causal impact of sleep loss on the basic desire to help another human being, but further characterised the central underlying brain mechanism associated with this altered phenotype of diminished helping. Specifically, sleep loss significantly and selectively reduced activity throughout key nodes of the social cognition brain network (see Fig 1B) normally associated with prosociality, including perspective taking of others’ mental state, their emotions, and their personal needs. Therefore, impairment of this neural system caused by a lack of sleep represents one novel pathway explaining the associated withdrawal of helping desire and the decisional act to offer such help.

The research is here.