What if the part of our brain that we thought was dedicated to visual information also processed other sensory information? Olivier Collignon, a neuropsychology professor, and his team conducted an investigation. The results represent a small revolution for neuroscience.
For 15 years, Olivier Collignon, an FNRS research associate and professor of cognitive neuroscience at UCLouvain, has focused on sensory loss and its consequences for the brain. As head of a research group called the Crossmodal Perception and Plasticity Lab (CPP Lab), he began his research by asking whether the blind develop capacities that exceed those of the sighted to compensate for their lack of vision. Quite recently, the researcher and his team set out on another challenge: studying the brain's perception of moving objects. The results are amazing.
What goes on in our occipital cortex?
The study, published in late May in the scientific journal Current Biology, focused on an area of the brain that processes visual information: the V5 area of the occipital cortex. When we see something move, say, a car, this area activates. When the car is static, the area is much less active. Historically, the occipital cortex has been studied as purely ‘visual’. According to established neuroscience, no auditory or tactile stimuli are processed in this area of the brain. Faced with this unequivocal scientific observation, Prof. Collignon asked: What if this area was also involved in the processing of non-visual information? What if this part of the brain could also process information from another of our senses? To find out, he and his team began with one observation: a moving image is very often accompanied by a sound. So where does the exchange of information between visual and auditory stimuli take place? What if it was in the occipital cortex, in the very early stages of information processing?
An experiment deep within the brain
For five years, in collaboration with the University of Trento (Italy), a UCLouvain team coordinated by CPP Lab PhD student Mohamed Rezk analysed brain activity maps created using magnetic resonance imaging (MRI). Each of 24 volunteer participants were stimulated visually and audibly while lying in a scanner. Moving images in certain directions as well as sounds in the same directions were presented to them. The researchers observed which brain areas became active for sounds and moving images. Using machine learning technology, they could even predict the information sent to participants simply by looking at their brain activity.
Decompartmentalising brain area functions
After analysing all of these brain activity maps, scientists are unanimous: the occipital cortex, initially considered only visual, processes information on moving sounds. However, our brain organisation is highly codified: the area dedicated to visual movement is also involved in auditory movement, but not in the recognition of a person's voice, for example. ‘Even more precisely,’ Prof. Collignon explains, ‘we noticed that each direction of movement had particular representations in the brain. The area that prefers to answer “to the right” for the visual direction also prefers to answer “to the right” for hearing. For our brain, the important thing isn’t the type of information (visual or auditory) but its function: What should I do with this information?’
A small revolution for neuroscience
This conclusion has caused quite a splash in the scientific world. Indeed, a cerebral area long perceived as solely visual is in fact not impenetrable to information from other senses. This finding is categorically opposed to classical neuroscience, which teaches that certain parts of the brain are unimodal and sensory information processing is compartmentalised.
Future research
‘This discovery opens up an incredible field of possibilities,’ Prof. Collignon says. In addition to this comprehensive study, CPP Lab members worked on other, more specific study elements (see boxes). In the years to come, Prof. Collignon will map connectivity between sensory areas, exploring for paths where information is transferred between sensory areas. ‘We also want to understand the link between the brain’s multisensory organisation and the mechanisms of transmodal plasticity that’s expressed in the event of sensory deprivation’ (see Box 1). These are all questions to which UCLouvain researchers hope to find answers. Because a scientist isn’t satisfied with hypotheses.
Lauranne Garitte
How do blind people process visual information?
In humans, the occipital cortex is the part of the brain known to process visual information. It detects human emotions, differentiates animals, recognises a tool or an environment. But what becomes of it in individuals who are born blind? This is the question Stefania Mattioni, a UCLouvain postdoctoral researcher and CCP Lab member, asked in a recent study published in eLife. To answer it, she presented eight categories of sounds to sighted and blind individuals as each lay in an MRI scanner – sounds made by people, tools, environments (such as the sound of waves), animals, etc. For the sighted individuals, Stefania Mattioni and her colleagues also presented corresponding visual images. The researchers were thus able to compare the brain activity of these two groups. And the result is surprising: ‘The way the blind categorise information responding to acoustic stimuli is similar to the organisation of visual information in sighted people.’ The occipital cortex in blind individuals retains its structure: the same areas of the cortex ‘prefer’ the same categories. This discovery gives rise to a broader question concerning what’s innate and what’s acquired: ‘What’s the share of innate and acquired in processing information?’ Dr Mattioni wonders. ‘In blind individuals, the usually massively visual areas markedly increase their response to sounds. Experience therefore influences the way our brain organises itself, with categories of sound that correspond to a certain visual image. This intrinsic organisation is therefore genetically programmed.’
Is there only one scientific truth?
In the midst of the coronavirus health crisis, we all rely on the decisions of experts. After all, they know the scientific truth. Or do they? Remi Gau, a UCLouvain postdoctoral researcher and CCP Lab member, along with Marco Barilari and Olivier Collignon, participated in a study that shows researchers don’t always agree, despite initially identical assumptions and data. The study was recently published in Nature.
Dr Gau and his colleagues participated in NARPS (Neuroimaging Analysis Replication and Prediction Study). Among 200 researchers around the world grouped into 70 teams, UCLouvain researchers analysed data from a decision-making experiment carried out using functional magnetic resonance imaging. They were asked to confirm or refute nine hypotheses (e.g. Do we observe an increase in activity in the prefrontal cortex when making a decision that can bring us more money?). Over three months, the teams analysed the data independently and provided a binary response (confirmed or denied) to each hypothesis. They were also asked to provide the brain activation maps generated for their analyses.
Dr Gau and his colleagues observed great variability between the teams in terms of binary responses. For five of the hypotheses, only 20 to 40% of the teams arrived at the same result. Even very similar intermediate results led to different conclusions. Hence there is considerable variability in results among researchers, even when the neuroimaging data and hypotheses are identical. Dr Gau emphasises the importance of transparency and sharing data and research results in ‘open-access’ mode so that the combined analysis of neuroimaging research can better highlight convergence between the teams.
A glance at Olivier Collignon's bio
After earning a master’s degree in psychology from the University of Liège and a master’s degree in cognitive science from UCLouvain, Olivier Collignon specialised in cognitive neuroscience, completing a PhD at UCLouvain on cerebral plasticity in case of blindness. He has pursued this subject throughout his career, including during two postdocs at the Université de Montréal’s Centre de recherche en neuropsychologie et cognition. Since 2012, he has led a UCLouvain research group called the Crossmodal Perception and Plasticity Lab (CPP Lab) and served as an associate professor at the University of Trento’s Center for Mind and Brain Science (CIMeC). Since 2016, he has been an FNRS research associate and associate professor at UCLouvain. His research is funded by multiple UCLouvain sources (e.g. FSR, Louvain Cooperation), the FNRS (e.g. MIS, EOS), and European sources (e.g. ERC Grant, Marie Curie). His research focuses on the general question: How does a brain area develop, maintain and change its sensory and functional role?