Laminar evoked responses in mouse somatosensory cortex suggest a special role for deep layers in cortical complexity

Abstract

It has been suggested that consciousness is closely related to the complexity of the brain. The perturbational complexity index (PCI) has been used in humans and rodents to distinguish conscious from unconscious states based on the global cortical responses (recorded by electroencephalography, EEG) to local cortical stimulation (CS). However, it is unclear how different cortical layers respond to CS and contribute to the resulting intra‐ and inter‐areal cortical connectivity and PCI. A detailed investigation of the local dynamics is needed to understand the basis for PCI. We hypothesized that the complexity level of global cortical responses (PCI) correlates with layer‐specific activity and connectivity. We tested this idea by measuring global cortical dynamics and layer‐specific activity in the somatosensory cortex (S1) of mice, combining cortical electrical stimulation in deep motor cortex, global electrocorticography (ECoG) and local laminar recordings from layers 1–6 in S1, during wakefulness and general anaesthesia (sevoflurane). We found that the transition from wake to sevoflurane anaesthesia correlated with a drop in both the global and local PCI (PCIst) values (complexity). This was accompanied by a local decrease in neural firing rate, spike‐field coherence and long‐range functional connectivity specific to deep layers (L5, L6). Our results suggest that deep cortical layers are mechanistically important for changes in PCI and thereby for changes in the state of consciousness.

Exploring effects of anesthesia on complexity, differentiation, and integrated information in rat EEG

“…2014 ). In a recent paper by Hönigsperger et al. (2024) , they suggested that deeper layers are relatively more important for PCI ST during wakefulness in mice, and L5/L6 is known to project to the thalamus ( Harris et al.…”

An integrative, multiscale view on consciousness theories_Eary version of paper in press in NEURON

“…Widespread theoretical agreement may increase such confidence and justify inference in more challenging cases. Furthermore, complexity and information richness can be studied at multiple levels (Figure 6), from human extracranial and intracranial recordings to rodents 139,[151][152][153][154] and cortical slices 155 . Outside of the human brain, in which they are calibrated, complexity measures do not allow any inference on the level of consciousness.…”