What kinds of brain activity correspond exactly to conscious experiences? How might those mechanisms have evolved, and are they shared across species?
What creates our conscious experience of the world around us? And how do specific patterns of brain activity that correlate to conscious experience transform into the subjective awareness we experience moment by moment?
To better understand patterns of brain activity that correspond to conscious experiences – known as neural correlates of consciousness (NCC) – the Templeton World Charity Foundation is funding an ambitious research project, the third in a series of Structured Adversarial Collaborations, a format that allows researchers to systematically evaluate competing hypotheses about consciousness through carefully designed experiments and rigorous cross-laboratory validation.
Bringing together four prestigious neuroscience laboratories, the project aims to test two competing theories that propose fundamentally different mechanisms for how consciousness emerges from neural activity. Specifically, does consciousness emerge from an explosion of activity in the brain's frontal regions, as put forth in the Global Neuronal Workspace Theory (GNWT), or does it arise from sustained patterns of information integration in the posterior regions of the brain, as proposed by the Integrated Information Theory (IIT)?
“The goal of this project, and the whole Templeton collaboration, is to improve theories of consciousness,” says project lead Dr. Yuri Saalmann, Professor of Psychology at the University of Wisconsin-Madison and core scientist at the Wisconsin National Primate Research Center.
“And, there are a number of reasons why this is vital. One is that it allows us to get a better understanding of consciousness, which can be useful for driving new experiments and discoveries; but also, so we can better understand consciousness disorders like coma, where right now there are very limited clinical options.”
To test predictions consistent with these two divergent theories, teams from the Geffen Lab at the University of Pennsylvania, the Olsen Lab at the Allen Institute, Biomedical Research Foundation Academy Of Athens (BRFAA), and the University of Wisconsin-Madison are using groundbreaking technology and innovative experimental designs to manipulate brain networks.
Neuropixels – electrodes capable of recording the activity of hundreds of neurons in the brain – will allow the researchers to record neural activity from both closely spaced neurons, as well as individual neurons across the anterior-to-posterior cerebral cortex. While optogenetics – a technique using light-sensitive proteins (derived from algae) to control specific neurons, and even deactivate different regions, by shining a light through optical fibers inserted into the brain – will allow them to observe the resulting effects on consciousness and perception. Together, these techniques will provide first-of-their-kind, high spatiotemporal resolution tests of, and potentially evidence for or against, each theory of consciousness, as well as insight into the evolution of patterns of brain activity that correspond to conscious experiences.
In addition to employing new technologies, the project will also shed light on whether mechanisms are shared across species. Unlike the other adversarial collaborations, the subjects of this project are non-human primates and mice, a deliberate choice that will allow researchers to explore how consciousness might have evolved.
"Mice have differences in the structure of their frontal lobe,” says Saalmann. “While the frontal region in mice is reduced compared to humans and macaques, some of the core regions overlap in their inputs and outputs, so the neuronal firing patterns during behavior are able to be compared across species.”
For this project, Saalmann and his colleagues designed animal model experiments to be able to record and manipulate brain activity with unprecedented precision in three key areas where the theories diverge:
“The key goal for us, in terms of this particular project, is getting data that allows us to inform theories of consciousness at a very small scale,” says Saalmann. “Previous work into human consciousness has been done using functional MRI or EEG techniques, which monitor large-scale brain activity patterns. So, we’ve been able to get a very good understanding of large-scale patterns of activity in the brain, but not much insight into what's happening at much smaller scales, like at the individual brain cell level.”
As Saalmann explains, brain cells generate electrical pulses known as action potentials, whose patterns across many different neurons encode our experience at any given time. By recording the activity of many cells at the finest resolution possible, the project’s researchers hope to isolate conscious perception from other cognitive processes.
Dr. Maria Geffen, an auditory neuroscientist at the University of Pennsylvania, leads one of the experimental teams testing the theories. Her laboratory specializes in understanding how the brain processes sensory information, particularly in the auditory cortex.
"My lab has made fundamental discoveries on the function of different types of networks in the brain," says Geffen. "We've identified a number of different cell types that support specific auditory computations, such as frequency discrimination or identifying sequences of sounds that you would hear in a melody."
Geffen's team has trained mice to respond to either auditory or visual targets. By also including "distractor" stimuli that mice must ignore, researchers are able to study pure perception without the confounding effects of reward-seeking behavior.
“In this study, we're looking at the propagation of the sensory signal through the brain as part of the consciousness framework,” says Geffen. “We're analyzing the neuronal activity while those stimuli are consciously perceived, but not when they're responded to by the mouse.
"Observing the neuronal activity during non-reward-based activities gives a more organic view of how the mice brain functions.”
For macaques, researchers developed a visual recognition task. The monkeys are trained to identify matching faces or objects while researchers record their neural activity. The training process takes anywhere from six to twelve months, depending on how difficult the complex task is, as well as the abilities of the animals.
Like with the mice, the experimental design is clever in its ability to separate perception from action. The macaques are presented with three conditions: A target visual stimulus that requires a response, a non-target face that does not require a response, and an irrelevant visual stimulus, which allows for the distinction between neural activity related to perception versus action. Researchers record neuronal activity while monitoring eye movements to track attention and awareness.
While the comparative study of two such divergent theories is potentially valuable for advancing the understanding of consciousness, it might also have broad implications for human health and medicine.
"Understanding how we consciously perceive things is fundamental to our understanding of the brain more generally," Geffen explains.
"You can have individuals experiencing hallucinations, you can have individuals who have a lesion, like a visual lesion or an auditory lesion, or you can have individuals with ADHD where just the level of attention varies from time to time."
The researchers expect to complete their experiments in approximately two years, and will subsequently submit their results for publication in a peer-reviewed journal. Information will be made available to the public through a registered report, a relatively new format in scientific publishing where researchers detail their experimental plans and analysis methods before conducting the experiments.
"Lionel Naccache [a key contributor and developer of GWNT] and Giulio Tononi [the developer of IIT] are on record about the predictions of their theories," confirms Saalmann. "Once we get approval of that first stage registered report, then we can start experiments to test these predictions.”
Rather than simply proving one theory right and another wrong, the project may well lead to something more nuanced. As Saalmann suggests, "Maybe the theories merge, maybe they just revise their theories to better fit the data. I don't think any theory will be the absolute truth on the matter."
This collaborative approach could serve as a model for future scientific research, especially in fields where multiple theories compete to explain complex phenomena.
"We're going to collect this huge data set, and we’re going to make it publicly available," says Geffen. "The data set will then be able to be used to test any number of hypotheses by researchers anywhere in the world."
By working together rather than in opposition, scientists may find that the truth about consciousness lies somewhere between or beyond their current theories, ultimately leading to better treatments for disorders of consciousness, as well as a deeper understanding of how our brains create our conscious experience of the world.
To better understand existing theories of consciousness, Templeton World Charity Foundation (TWCF) funds a series of 5 ambitious research projects, known as Structured Adversarial Collaborations, to allow researchers to evaluate competing hypotheses through carefully designed experiments and rigorous cross-laboratory validation.
This blog is part of a series that complements the launch of Accelerating Research, a unique platform developed by Dawid Potgieter and DataCite with TWCF funding, showcasing results from each Structured Adversarial Collaboration project as it progresses.
