Denis le Bihan
Denis le Bihan

CANCELLED: DCCN Colloquium Denis Le Bihan

Thursday 13 June 2024, 2 pm - 3 pm
The dimensions of the brain connectome



Denis Le Bihan1,2,3 

  1. NeuroSpin, Frédéric Joliot Institute for Life Sciences (Commissariat à l’Energie Atomique, CEA), Centre d'études de Saclay, Paris-Saclay University, Bâtiment 145, 91191 Gif-sur-Yvette, France 
  2. Human Brain Research Center, Kyoto University, Kyoto, Japan 
  3. Department of System Neuroscience, National Institutes for Physiological Sciences, Okazaki, Japan 

    There is an upper limit on the action potential propagation speed in the brain. Functional “distances” between neural nodes (geodesics), thus, depend on both the spatial distances between nodes and the time to propagate between them, through a connectome spacetime with four intricated dimensions, a view common to the relativity theory. Furthermore, propagation speed depends on axonal length: longer fibers carry faster speeds because they are surrounded by a thicker myelin sheath. The density of functional connections is known to decrease in patients in minimally conscious states, with the disappearance of the short (slow) connections to the benefit of long-range (fast) connections. This suggests that conscious activity must be associated to a slowdown of the overall propagation speed, in as similar way a gravitational field slows the speed of light according to general relativity. Neural nodes act as “masses” which, depending on their degree of activation, curve the connectome spacetime and the flow of action potentials (brainlines) around them. This curvature may be estimated from MRI, providing a quantitative signature of consciousness. Furthermore, a clue to bridge the apparent gap between the microscopic and macroscopic connectome scales may be found in the AdS/CFT correspondence.  Applied to the relativistic brain connectome, this means that consciousness is the emergence in a 5D spacetime of the neural activity present as its boundaries, the 4D cortical spacetime. Consciousness would, thus, be a holographic 5D construction by our inner brain emerging from connections between events present at the surface of its material 4D connectome. In other words, the conflict between ‘consciousness and matter’ could be resolved by considering that the spacetime of our cerebral connectome has five dimensions, the fifth dimension allowing the natural, immaterial emergence of consciousness as a dual form of the 4D spacetime embedded in our material cerebral cortex. 

Thursday 13 June 2024, 2 pm - 3 pm
Denis Le Bihan
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