Humans are unrivaled in cognition. After all, no other species has sent probes to other planets, produced life-saving vaccines, or created poetry. How information is processed in the human brain to make this possible is a question that has generated endless fascination, but no definitive answer.
Our understanding of brain function has changed over the years. But current theoretical models describe the brain as a “distributed information processing system”. This means that it has separate components, which are intertwined by brain wiring. To interact with each other, the regions exchange information through a system of input and output signals.
However, this is only a small part of a more complex picture. In a study published in Nature Neuroscience, using evidence from different species and multiple neuroscience disciplines, we show that there is not just one type of information processing in the brain. The way information is processed also differs between humans and other primates, which may explain why our species’ cognitive abilities are so superior.
We have borrowed concepts from what is known as the mathematical framework of information theory – the study of the measurement, storage and communication of digital information crucial to technologies such as the Internet and the Internet. intelligence – to track how the brain processes information. We found that different regions of the brain actually use different strategies to interact with each other.
Some regions of the brain exchange information with others in a very stereotypical way, using input and output. This ensures that the signals are transmitted reproducibly and reliably. This is the case of specialized domains for sensory and motor functions (such as the processing of sound, visual and movement information).
Take the eyes, for example, which send signals to the back of the brain for processing. The majority of the information sent is duplicated, being provided by each eye. In other words, half of this information is not necessary. We therefore call this type of input-output information processing “redundant”.
But redundancy brings robustness and reliability – it’s what allows us to still see with one eye. This ability is essential for survival. In fact, it’s so crucial that the connections between these brain regions are anatomically wired into the brain, much like a landline telephone.
However, not all information provided by the eyes is redundant. Combining information from both eyes ultimately allows the brain to process depth and distance between objects. It is the basis of many kinds of 3D glasses in cinema.
This is an example of a fundamentally different way of processing information, in a way greater than the sum of its parts. We call this type of information processing – when complex signals from different brain networks are integrated – “synergistic”.
Synergistic processing is most prevalent in brain regions that support a wide range of more complex cognitive functions, such as attention, learning, working memory, social and numerical cognition. It is unwired in the sense that it can change in response to our experiences, connecting different networks in different ways. This makes it easier to combine information.
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These areas where many synergies take place – mainly in the front and middle of the cortex (the outer layer of the brain) – integrate different sources of information from the whole brain. They are therefore more widely and more effectively connected to the rest of the brain than the regions that process primary sensory and movement-related information.
The high-synergy areas that support information integration also typically feature many synapses, the microscopic connections that allow nerve cells to communicate.
Is synergy what makes us special?
We wanted to know if this ability to accumulate and construct information through complex networks across the brain is different between humans and other primates, which are evolutionarily close relatives of ours.
To find out, we looked at brain imaging data and genetic analyzes from different species. We found that synergistic interactions account for a higher proportion of total information flow in the human brain than in macaque monkey brains. In contrast, the brains of the two species are equal in terms of the amount of redundant information.
However, we also looked specifically at the prefrontal cortex, an area at the front of the brain that supports more advanced cognitive functioning. In macaques, redundant processing of information is more prevalent in this region, whereas in humans it is an area of high synergy.
The prefrontal cortex has also undergone significant expansion with evolution. When we looked at data from chimpanzee brains, we found that the more a region of the human brain had evolved in size compared to its chimpanzee counterpart, the more that region relied on synergy.
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We also reviewed genetic analyzes of human donors. This showed that brain regions associated with synergistic information processing are more likely to express genes that are uniquely human and related to brain development and function, such as intelligence.
This led us to the conclusion that additional human brain tissue, acquired as a result of evolution, could be primarily dedicated to synergy. In turn, it is tempting to speculate that the benefits of greater synergy may, in part, explain our species’ additional cognitive abilities. The synergy may add an important piece to the puzzle of human brain evolution, which was previously missing.
Ultimately, our work reveals how the human brain navigates the trade-off between reliability and information integration – we need both. Importantly, the framework we have developed promises critical new insights into a wide range of neuroscientific questions, from those in general cognition to disorders.