Activity in hand- and tool-selective regions for prosthetic limbs in amputees is associated with prosthesis usage in everyday life.
van den Heiligenberg F., Macdonald S., Duff E., Henderson Slater D., Johansen-Berg H., Culham J., Makin T.
The lateral occipitotemporal cortex (LOTC) contains subregions differentially responding to specific object categories, such as body parts and tools. This selectivity may relate to action knowledge, rather than visual properties of the objects. Prosthetic limbs share different commonalities with hands and tools (in terms of both visual and action features). Specifically, cosmetic prostheses look like hands, but can be used as tools (elongate the stump), whereas functional prostheses ("hook") do not resemble hands, but can be used as such (e.g. grasping). Here we presented images of functional and cosmetic prosthetic arms to 32 individuals with acquired or congenital limb loss, in an event-related fMRI paradigm. Hand- and tool-selective regions were identified using an independent localiser. Prosthesis usage was assessed in questionnaires and ecological behavioural measurements. We predicted that activation in hand- and tool-selective regions for prosthetic limbs would reflect the action-related properties of the prosthetic limb and would increase with usage. To identify the relationship between fMRI activation during viewing of prosthetic limb images and prosthesis use in everyday life, a whole-brain voxel-wise partial correlation was carried out (accounting for activation to objects). We found a significant correlation between prosthesis use and activation in LOTC and the posterior intraparietal sulcus for both functional and cosmetic prostheses. These regions overlapped with hand- and tool-selective regions. Strikingly, correlations with usage revealed activation patterns that reflect action knowledge, rather than visual properties. Specifically, cosmetic (hand-like) prostheses showed a left-lateralised pattern consistent with tool representation. Functional prostheses, whereas visually more similar to tools, show bilateral activation patterns, consistent with hand representation. Our findings suggest that ecological behaviour, in the form of prosthetic limb use, can shape how high-level visual cortex responds to visual stimuli. Further research will aim to determine how information in LOTC is shared across categories such as hands, tools, and prostheses. Meeting abstract presented at VSS 2015.