Unravelling the mysteries of perception and consciousness
How does the human cortex operate? What makes us intelligent? How can we better understand conscious perception? Over the past 20 years, Matthew Larkum, professor of neuronal plasticity at Humboldt University of Berlin, has been considering the relationship between the information within the cortex and the main neurons that make up this part of our brains. The goal is to understand the cellular mechanisms that underlie the ability of the cortex to link sensory information with previous experience. To build on his work conducted at Larkum Lab, Larkum has hosted the MECHPREDPRO project, supported by the EU, with the principle investigator Jaan Aru.
A better understanding of how cells interpret information
The project started with the observation that the main output cells of the cortex – the pyramidal cells – have two distinct parts. These two parts receive different inputs, one gets internally generated information and the other externally generated information. Larkum has long hypothesised that the properties of these cells allow them to predict and interpret the information they receive from the outside world. If the internal and external inputs to the neuron match, the cell is recruited to fire vigorously in a manner that can be detected downstream. In other words, a ‘match’ with expectation is broadcast to the rest of the brain. The main result of this EU-funded project is a theory of consciousness that takes the cellular perspective on this mysterious aspect of our lives. “There are many interesting ideas about consciousness, some of which seem a bit too far-fetched. Ours is a neurobiological theory: we start from the facts that are known about cellular processes and take it from there,” says principle investigator Aru whose work was supported by the EU’s Marie Skłodowska-Curie Actions programme.
The impact of predictions on conscious experience
Unlike most previous theories, Aru’s paper Cellular mechanisms of conscious processing published in Trends in Cognitive Sciences, ties consciousness to cellular-level events. He proposes that consciousness is dependent on the interaction between the different compartments of pyramidal cells, modulated by subcortical structures like the thalamus. The fact that the parts of neurons which carry internal information have a crucial influence on conscious experiences, is in line with research showing that conscious experience is modulated by predictions and prior knowledge. “Fascinating experiments have shown that expectations can create experience of objects that are actually not there in the real world. Such illusory perception is not only pathological, but can also happen in healthy humans, for example if we expect something to happen or the context suggests that some object should be there,” reports Aru. The researchers have further proposed how these fundamental cellular properties can explain phenomena like dreams and illusory perception, which Aru explores in his paper Apical drive – A cellular mechanism of dreaming? published in Neuroscience & Biobehavioral Reviews. In dreams, input from within the brain itself dominates the output of the sensory neurons and hence dictates what we experience while asleep. The insight into how our brains process and react to internal and external information brings us closer to understanding the nature of human consciousness and there are potential applications to such knowledge. “Knowing these details will put us in a very strong position to investigate cognitive pathologies and also to contribute to the burgeoning field of artificial neural networks with biologically inspired suggestions,” says Larkum, who supervised the research.
Keywords
MECHPREDPRO, cortex, neurons, apical drive, prediction, pyramidal cells
