High-level sensory and motor regions encode object mass after real-world object interactions

We experience real-world objects not just by seeing them but by interacting with them. Such interactions give us information about their physical properties such as mass. Are such physical properties integrated into the underlying object representations? To investigate this fundamental question, we performed wireless brain recordings from two monkeys with electrodes implanted into high-level sensory and motor regions before and after they interacted with real-world objects of varying mass. We created 5 water bottles painted with different colors, and added weights (100-500 grams) chosen to be uncorrelated with their (R,G,B) colors. We then recorded neural responses to images of these bottles on a screen while each animal passively viewed these images, prior to any interaction with these bottles. Each bottle was then loaded with a small juice reward and presented to each monkey in randomized order. Monkeys readily interacted with these bottles, lifting them up to drink the juice, thereby ensuring that they had experience with the varying masses of these bottles. Following these interactions, we again recorded neural responses to images of these bottles on a screen as before. We hypothesized that neural activity would show a greater correspondence with the experienced mass of these objects, following the real-world interaction compared to before the interaction. To this end, we calculated the correlation between the multiunit firing rate from each electrode with the object mass. Our main finding is that neural responses showed an increased correlation with object mass after real-world interactions. This effect was present in the premotor/prefrontal cortex (PMv/vlPFC) as well as in inferior temporal cortex (IT). Taken together, our results show that object mass is rapidly encoded into both high-level sensory and motor regions of the brain following real-world interactions with objects.