Knowing about tools: neural correlates of tool familiarity and experience.

The observation of tools is known to elicit a distributed cortical network that reflects close-knit relations of semantic, action-related, and perceptual knowledge. The neural correlates underlying the critical knowledge of skilled tool use, however, remain to be elucidated. In this study, functional magnetic resonance imaging in 14 volunteers compares neural activation during the observation of familiar tools versus equally graspable unfamiliar tools of which the observers have little, if any, functional knowledge. In a second paradigm, the level of tool-experience is investigated by comparing the neural effects of observing frequently versus infrequently used familiar tools. Both familiar and unfamiliar tools activate the classic neural network associated with tool representations. Direct comparison of the activation patterns during the observation of familiar and unfamiliar tools in a priori determined regions of interest (p<0.05, corrected) reveals activation in the temporal (left lateral posterior middle temporal gyrus) and parietal cortices (left supramarginal gyrus, left inferior parietal lobule, and left precuneus). It is hypothesized that the parietal activity underlies tool-use knowledge, with supramarginal gyrus storing information about limb and hand positions, and precuneus storing visuospatial information about hand-tool interactions. As no frontal activation survived this contrast, it appears that premotor activity is unrelated to experience based motor knowledge of tool use/function, but rather, is elicited by any graspable tool. Confrontation with unfamiliar or infrequently used tools reveals an increase in inferior temporal and medial and lateral occipital activation, predominantly in the left hemisphere, suggesting that these regions reflect visual feature processing for tool identification.