As neuroscientists sort through the conflict between the two leading theories of consciousness — Integrated Information Theory (IIT) and Global Workspace Neuronal Theory (GNWT) — we might want to look at a third, quite different contender.

University of Oslo neuroscientist Johan Storm, trying to interpret the spate of recent events at Science Norway, points to dendritic integration theory (DIT) That is, consciousness is a function of brain cell reactions:

“Every single neuron is like a computer. It has thousands of molecular mechanisms that process information in intricate ways within the cell. At the same time, each cell can have more than 20,000 connections to other neurons,” says Storm.

The cell has an extremely complicated system of connections and feedback loops, where new information that comes in through the system is matched with information the brain already has.

In certain situations, when new and old information match, an almost explosive reaction occurs where the cell sends a flurry of nerve impulses to other cells, according to Storm.

Ingrid Spilde,“Why do we have consciousness? Researchers are deeply divided,” Science Norway, June 11, 2024 Translated by Ingrid P. Nuse

And that explosive reaction, according to some neuroscientists, produces consciousness.

A way of understanding how anesthesia works

From a recent article at Neuron, comparing theories, of which Storm was the first author:

The fundamental insight of DIT is that L5 cortical pyramidal neurons both receive and process categorically different information in two distinct regions: the apical and basal compartments that are separated both physically and functionally. The electrical separation between these two compartments, which is already substantial, is accentuated by a high “leak” conductance that allows apical and somatic computations to be essentially isolated from each other. However, it is now well established that these neurons can associate information arriving at both compartments through highly non-linear processes dependent on voltage-sensitive ion channels in the dendrites121,122 and controlled by very specifically targeted inhibition and neuromodulation impinging on subdomains of the dendritic tree.126 DIT hypothesizes firstly that the basal compartment of these neurons receives predominantly feedforward information that relates to the specific cognitive or sensory feature being processed in the column the L5 pyramidal neuron. Second, it proposes that long-range feedback information impinges predominantly on the apical compartment of the same neurons providing information (or context) about processes occurring elsewhere in the brain, including other areas of the cortex.

Storm JF, Klink PC, Aru J, Senn W, Goebel R, Pigorini A, Avanzini P, Vanduffel W, Roelfsema PR, Massimini M, Larkum ME, Pennartz CMA. An integrative, multiscale view on neural theories of consciousness. Neuron. 2024 May 15;112(10):1531-1552. doi: 10.1016/j.neuron.2024.02.004. Epub 2024 Mar 5. PMID: 38447578. The paper is open access.

Storm thinks that the theory provides a cogent explanation for general anesthesia: Anesthetics “inhibit the brain cells’ ability to communicate internally and compare information. Thus, they never gets to send the flurry of impulses that yield conscious experiences.”

As the developers of DIT explained recently,

We recently proposed the dendritic integration theory [DIT; 63,64], which hypothesizes that consciousness depends on the reintegration of top-down information via the apical dendrites of layer 5 pyramidal neurons. DIT is based on the empirical finding that the electrical coupling between apical and basal dendrites of cortical pyramidal neurons is disrupted by common anesthetics, thus blocking the influence of the apical dendrite on the output of the layer 5 pyramidal neurons [65]. According to this theory, decoupling the apical from the basal dendrites in a sufficiently large number of cortical pyramidal neurons would switch off consciousness. Essentially, DIT pinpoints the nexus of information flow within the brain microarchitecture that is crucial for consciousness. Besides the clinical benefit and understanding of the computation involved, DIT offers a framework for interrogating this biological mechanism in the laboratory.

Gidon A, Aru J, Larkum ME. Does brain activity cause consciousness? A thought experiment. PLoS Biol. 2022 Jun 10;20(6):e3001651. doi: 10.1371/journal.pbio.3001651. PMID: 35687582; PMCID: PMC9187086. The paper is open access.

Of course, the fact that the theory can account for the loss of consciousness doesn’t entail that it can account for the existence or origin of consciousness. There are doubtless other factors involved.

What we are really learning is that even the individual cells that mediate consciousness are very complex — even in the lab rats used in the experiments. We shouldn’t expect a simple theory that just comes along and explains human consciousness in a plausible way. As the famous saying, often attributed to Einstein, goes, “Everything should be made as simple as possible, but not simpler.”

You may also wish to read: Consciousness Wars: Researcher tries negotiating a truce. Witch hunts against leading theories are bad for a discipline’s reputation; Neuroscientist Johan Storm thinks that all the prominent theories of consciousness are a little bit right. The fate of the discipline may depend on how committed researchers are to finding out the facts vs. protecting a materialist view of consciousness.