Humans have no rival in the area of 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 it possible is a question that has caused endless fascination, but no definitive answers.
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 different components, which are closely connected through the wiring of the brain. To interact with each other, regions exchange information through a system of input and output signals.
However, this is only a small part of a more complex image. In a study published in Nature Neuroscience, using evidence from different species and multiple neuroscientific disciplines, we show that there is no single 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 measuring, storing and communicating digital information that is crucial for technologies such as the Internet and artificial intelligence, to keep track of of 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 inputs and outputs. This ensures that signals are transmitted in a reproducible and reliable manner. This is the case for areas that specialize in sensory and motor functions (such as the processing of sound, visual, and movement information).
Take the eyes, for example, that send signals to the back of the brain to process them. Most of the information that is sent is duplicated, provided by each eye. Half of this information, that is, is not necessary. So we call this type of input-output information processing “redundant.”
But redundancy provides robustness and reliability – that’s what allows us to see even with one eye. This ability is essential for survival. In fact, it is so crucial that the connections between these brain regions are anatomically wired to the brain, much like a landline.
However, not all information provided by the eyes is redundant. The combination of the information from the two eyes finally allows the brain to process the depth and distance between objects. This is the basis of many types of 3D glasses in cinema.
This is an example of a fundamentally different way of processing information, in a way that is 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 more common in regions of the brain that support a wide range of more complex cognitive functions, such as attention, learning, working memory, social and numerical cognition. It is not wired in the sense that it can change in response to our experiences, connecting different networks in different ways. This facilitates the combination of information.
The human brain is extremely complex. Shutterstock
These areas where a lot of synergy occurs, mainly in the front and middle part of the cortex (the outer layer of the brain), integrate different sources of information from the whole brain. Therefore, they are more broadly and efficiently connected to the rest of the brain than the regions that process primary, motion-related sensory information.
Areas of high synergy that support the integration of information also often have many synapses, microscopic connections that allow nerve cells to communicate.
Is synergy what makes us special?
We wanted to know if this ability to accumulate and build information through complex networks across the brain is different between humans and other primates, which are close relatives of ours in evolutionary terms.
To find out, we analyzed brain imaging data and genetic analysis of different species. We found that synergistic interactions represent a higher proportion of the total flow of information in the human brain than in the brains of macaque monkeys. In contrast, the brains of both species are the same in terms of how much they depend on redundant information.
However, we also looked specifically at the prefrontal cortex, an area in the front of the brain that supports more advanced cognitive functioning. In macaques, redundant information processing is more common in this region, while in humans it is an area with a lot of synergy.
The prefrontal cortex has also undergone significant expansion with evolution. When we examined the chimpanzee brain data, we found that the more a region of the human brain expanded during evolution in size relative to its chimpanzee counterpart, the more this region depended on synergy.
Rhesus macaque monkeys at Swayambhunath temple in Nepal. Shutterstock
We also analyzed genetic analyzes of human donors. This showed that brain regions associated with synergistic information processing are more likely to express genes that are exclusively human and related to brain development and function, such as intelligence.
This led us to the conclusion that the additional human brain tissue, acquired as a result of evolution, can be devoted primarily to synergy. In turn, it is tempting to speculate that the benefits of greater synergy may, in part, explain the additional cognitive abilities of our species. Synergy can add an important piece to the puzzle of the evolution of the human brain, which was previously missing.
Ultimately, our work reveals how the human brain navigates the trade-off between reliability and the integration of information: we need both. It is important to note that the framework we have developed promises new critical ideas on a wide range of neuroscientific questions, from general cognition to disorders.