A connectome-based model of conscious access in monkey cortex

Abstract

A growing body of evidence suggests that conscious perception of a sensory stimulus triggers an all-or-none activity across multiple cortical areas, a phenomenon called 'ignition'. In contrast, the same stimulus, when undetected, induces only transient activity. In this work, we report a large-scale model of the macaque cortex based on recently quantified structural connectome data. We use this model to simulate a detection task, and demonstrate how a dynamical bifurcation mechanism produces ignition-like events in the model network. Within this framework, the model predicts that feedforward excitatory transmission is primarily mediated by the fast AMPA receptors to ensure rapid signal propagation from sensory to associative areas. In contrast, a large fraction of the inter-areal feedback projections and local recurrent excitation depend on the slow NMDA receptors, to ensure ignition of distributed frontoparietal activity. Our model predicts, counterintuitively, that fast-responding sensory areas contain a higher ratio of NMDA to AMPA receptors compared to association cortical areas that show slow, sustained activity. We validate this prediction using in-vitro receptor autoradiography data. Finally, we show how this model can account for various behavioral and physiological effects linked to consciousness. Together, these findings clarify the neurophysiological mechanisms of conscious access in the primate cortex and support the concept that gradients of receptor densities along the cortical hierarchy contribute to distributed cognitive functions.

Distributed evidence accumulation across macaque large-scale neocortical networks during perceptual decision making

“…The alteration in winning onset order could indicate a change in the role of certain areas when the macaque encountered a tough vs simple task. This suggests that an efficient performance on difficult decision-making tasks might benefit from top-down modulation, a prediction aligned with conscious perception theories (Joglekar et al, 2018; Klatzmann et al, 2023; Mashour et al, 2020; Vugt et al, 2018). There is also evidence of monkeys taking different strategies depending on task difficulty (Brunet and Jagadeesh, 2019; Hyafil and Moreno-Bote, 2017).…”

Predicting distributed working memory activity in a large-scale mouse brain: the importance of the cell type-specific connectome

“…Previous large-scale models of the human and macaque cortex have replicated functional connectivity (Deco et al 2014; Demirtaş et al 2019; Honey et al 2007; Schmidt et al 2018; Shine et al 2018; Cabral et al 2011; Wang et al 2019) and propagation of information along the cortical hierarchy (Chaudhuri et al 2015; Joglekar et al 2018; Diesmann et al 1999). More recently, large-scale neural circuit models have been developed specifically to reproduce neural activity during cognitive tasks (Mejias and Wang 2022; Froudist-Walsh et al 2021; Klatzmann et al 2022). These models consider the fact that in the macaque cortex, the density of spines on pyramidal cells increases along the cortical hierarchy (Elston and Rosa 1998; Elston 2007; Chaudhuri et al 2015).…”

“…We propose that there is a greater functional specialization in the primate cortex which is afforded by the sparser and more targeted patterns of connectivity at the single-cell and area levels. Other differences to explore in future computational models include the ratio of NMDA to AMPA-mediated synaptic currents, which is approximately constant in the mouse cortex (Myme et al 2003) but varies along the cortical hierarchy in primates (Yang et al 2018; Klatzmann et al 2022), as well as hierarchy, which is defined based on feedforward and feedback projections in the mouse (Harris et al 2019) and primate (Markov et al 2014a).…”

Conscious Perception and the Prefrontal Cortex A Review

“…If feedback from PFC is involved in all instances of conscious perception-as relationalist theories would have it-deficits impacting these feedback connections should affect conscious perception while also sparing unconscious perceptual effects which depend on feedforward activity. This prediction, or something close to it, can be tested partly because feedforward and feedback propagations of activity rely on somewhat different neurobiological mechanisms (Froudist-Walsh et al 2021;Goulas et al 2021;Klatzmann et al 2022;Self et al 2012;Yang et al 2018). Fast excitatory feedforward transmission seems to depend in large part on AMPA receptors.…”

“…Correlational evidence from contrastive analysis is not the only source of evidence for prefrontalism. Causal evidence also provides an increasingly consistent picture in which feedback from PFC is critical for consciousness, and has the potential to reveal mechanisms down to the cellular level (Almeida, 2022;Aru et al 2020;Klatzmann et al 2022;Mashour et al 2020). 11 While this is clearly a fruitful application of no-report paradigms, prefrontal theories other than global workspace have no business to do with the P3b wave.…”