Decoding mental states from brain activity in humans

Understanding whether cognitive and perceptual states can be decoded from brain activity alone is a fundamental question in cognitive neuroscience. It is not only relevant for scientific theories of how information is encoded in the brain, but also has important practical and ethical implications.Non-invasive techniques such as functional MRI (fMRI) can be used to record signals related to brain activity in humans from many locations in the brain simultaneously. However, many conventional approaches to analysing these data rely on considering signal changes at each location independently of all the other locations in the brainThese conventional approaches have proven successful in elucidating many aspects of the relationship between cognitive and mental states and brain activity. However, recent advances in data analysis procedures raise the possibility of deciphering additional and complementary information from neuroimaging data.Recently, a powerful approach has emerged that applies pattern-recognition techniques to neuroimaging data. The new strategy is to decode a person's current mental state by learning to recognize characteristic spatial patterns of brain activity associated with different mental states. This takes into account not just activity at single locations but the full spatial pattern of activity. Such pattern-based decoding reveals that substantially more information is encoded in fMRI signals than was previously recognised.These new approaches have a particular use in addressing the question of how information regarding perceptual and cognitive states is encoded in the human brain. Pattern-based decoding has now been successfully used to reveal the principles underlying the representation of objects in the ventral visual pathway. It can also reveal conscious and unconscious sensory representations of individual features, and can be used to track dynamic changes in the contents of consciousness over time.Decoding approaches therefore provide a particularly sensitive way to determine what types of information are represented in the spatially distributed pattern of brain responses recorded with current neuroimaging techniques. However, for more general applications, important technical and methodological barriers remain to be overcome, including the ability of such approaches to generalize across individuals and different cognitive and perceptual states.As these techniques have the possibility to reveal covert or unconscious mental states, they raise important ethical and privacy concerns. These can be addressed within existing ethical frameworks, but nevertheless necessitate careful and considered engagement by the neuroimaging community.