The team used fMRI scans of patients to work out which how which regions of their brains process different categories of information (right). They were then able to show the regions on a virtual 3D brain (left)
Scientists have put together the first ever map of how the brain organises the thousands of images that come flooding in through our eyes every day. A team at the University of California, Berkeley, have found that the brain is wired to put in order all the categories of objects and actions that we see. To illustrate their findings, they have created the first map of how the brain organises these categories across the cortex.
Click here to open the interactive version of the map in a new window (may take some time to load)
The result â?? achieved through computational models of brain imaging data collected while test subjects watched hours of video clips â?? is what researchers call 'a continuous semantic space'. The UC Berkeley team have mapped this data across the human cortex to show which areas of the brain deal with which categories of objects we see in the world around us. Some relationships between categories make sense - for example, that humans and animals share the same 'semantic neighbourhood' - while others - like the apparent link between hallways and buckets - seem less obvious. Nevertheless, the researchers found that different people share a similar semantic layout.
The Berkeley team used functional Magnetic Resonance Imaging (fMRI) to record the brain activity of five researchers as they each watched two hours of film clips. Researchers then analysed the readings to find correlations in data and build a model showing how each of 30,000 subdivisions in the cortex responded to the 1,700 categories of objects and actions shown. Next, they used principal components analysis, a statistical method that can summarize large data sets, to find the 'semantic space' that was common to all the study subjects. The results are presented in multicoloured, multi-dimensional maps showing the more than 1,700 visual categories and their relationships to one another.
Categories that activate the same brain areas have similar colours. For example, humans are green, animals are yellow, vehicles are pink and violet and buildings are blue. 'Our methods open a door that will quickly lead to a more complete and detailed understanding of how the brain is organised,' said Alexander Huth, lead author of the study published yesterday in the journal Neuron. 'Already, our online brain viewer appears to provide the most detailed look ever at the visual function and organisation of a single human brain.'
His and his colleagues findings show that the brain efficiently represents the diversity of categories in a compact space. Instead of having a distinct brain area devoted to each category, as previous work had identified, for some but not all types of stimuli, the researchers found brain activity is organised by the relationship between categories. 'Humans can recognise thousands of categories. Given the limited size of the human brain, it seems unreasonable to expect that every category is represented in a distinct brain area,' said Mr Huth.
A clearer understanding of how the brain organises visual input can help with the diagnosis and treatment of brain disorders. The findings may also be used to create brain-machine interfaces, particularly for facial and other image recognition systems. 'Our discovery suggests that brain scans could soon be used to label an image that someone is seeing, and may also help teach computers how to better recognise images,' said Mr Huth.
He has produced a video and interactive website to explain the science of what the researchers found. It was long believed that each category of object or action humans see â?? people, animals, vehicles, household appliances and movements â?? is represented in a separate region of the visual cortex. But this new study shows that these categories are actually represented in highly organised, overlapping maps that cover as much as 20 per cent of the brain, including the somato-sensory and frontal cortices.
'Using the semantic space as a visualisation tool, we immediately saw that categories are represented in these incredibly intricate maps that cover much more of the brain than we expected,' Mr Huth said. Dr Jack Gallant, at whose laboratory the work was carried out, said: 'Discovering the feature space that the brain uses to represent information helps us to recover functional maps across the cortical surface. 'The brain probably uses similar mechanisms to map other kinds of information across the cortical surface, so our approach should be widely applicable to other areas of cognitive neuroscience.'
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