Is the visual machinery inside your brain the same as in mine?

Jun 18, 2024

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15 August 2023

It has been long believed that our brain’s fundamental architecture is organised in a similar way from person to person. We have assumed that everyone’s visual cortex will be in a similar position and occupy a similar area in each person’s brain. It turns out that is not the case.

Professor Marcello Rosa is the Head of Monash BDI's Neuroscience Program, and Head of the Structure, function and plasticity of the cerebral cortex Lab. He is co-senior author together with Dr Alex Puckett (The University of Queensland) on a paper exploring brain organisation with a particular focus on the visual cortex.

Professor Rosa said that surprisingly little is known about how variable human brains are in terms of their functional organisation.

“Do all human brains have the same areas in the cerebral cortex - the part involved in conscious perception, skilled action, and cognitive processes? Are these areas organised in the same way in you and me?” Professor Rosa said.

“In this study we have used the representations of the retina in the visual cortex - features which can be precisely quantified using functional magnetic resonance imaging - to gain insight on this question,” he said.

The researchers’ focus was on the second and third visual areas (also known as V2 and V3). These were among the first visual areas to be mapped in detail, more than fifty years ago. They have since been thought of as being organised in a stereotypical manner across individuals.

Schematic representation of the brain showing the canonical visual cortex (V) areas: V1 (Yellow) V2 (Orange) V3 (Blue) Image: Wikimedia Commons

An unexpected and high degree of variability was observed across brains. The research found that the “text book” view of the organisation of V2 and V3 only applied to one third of the individuals in the study, with the other two thirds showing more complex geometric mappings of the retina onto the cortex.

This work raises important questions about the developmental mechanisms responsible for the formation of visual maps, and indicates that significant variation exists within a healthy population's brains.

“This means that how our brains set up a function such as vision, that you’d think was relatively hard-wired - effectively an evolutionary template without much variation - could be much more dependent on our early interaction with our environment,” Professor Rosa said.

“We used data from the Human Connectome Project (HCP) database. One of the remarkable things is that all the participants in this study were regarded as having normal visual function. You wouldn’t have a clue that their visual pathway was organised differently. Visual function is achieved regardless, but the brain mapping that has taken place varies markedly from person to person,” he said.

Dr Elizabeth Zavitz who was a Group Leader in Monash BDI until recently, worked on the analysis with first author PhD student Fernanda Ribeiro (based at The University of Queensland).

“Fernanda undertook a novel approach to the analysis, repurposing a measure of similarity common in the machine learning field to make pairwise comparisons between the brains of participants. This allowed us to do a cluster analysis and demonstrate that there is more than one ‘typical’ brain organisation within the HCP data set,” Dr Zavitz said.

From the practical side, the research also raises questions about how reliably the locations and internal organisation of areas can be predicted based on brain “templates" (average maps, which are extensively used in brain research).

Joint senior author, Dr Alex Puckett, a Research Fellow at The University of Queensland said it has become increasingly common for researchers to define the location of cortical visual areas using a template-based approach, rather than empirical measurements.

“Our work strongly urges caution in doing so. To be accurate, these predictions must be able to account for the high degree of variability we’ve uncovered,” Dr Puckett said.

“Down the track medical practice is looking at developing and implanting brain computer interface devices, such as that pioneered by Monash’s Bionic Vision Group. We will need individualised brain maps for that. This kind of basic research gives us an insight into the variability we can expect to find,” Professor Rosa said.

Read the full paper, published in eLife, Variability of visual field maps in human early extrastriate cortex challenges the canonical model of organization of V2 and V3.

DOI: 10.7554/eLife.86439

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