We performed several fMRI experiments on three different special populations to address the role of sensorimotor experience.
We studied the representation of non-sensory, semantic information in congenitally blind and upper limb dysplasic (ULD; born without hands) subjects. We scanned with fMRI as subjects were presented with concepts which are either sensorily concrete (e.g. every-day objects), fully abstract (e.g. “justice”), imperceptible by the different subject groups (impossible to physically perceive or utilize motorically; e.g. a rainbow to a man blind from birth, a bimanually-handled tool to a ULD person) and perceptible (sensorily accessible; e.g. rain to a blind man and a usable tool to a ULD person).
Different parts of the brain, in the left anterior temporal lobe (lATL), showed preference for imperceptible and perceptible concepts in the blind. These two regions in lATL belong to different functional neural networks, as found in brain resting-state fluctuations. These findings support classical cognitive theories, showing that concepts’ symbolic and non-sensory representations can be processed separately from sensory-motor features, and suggesting the division of labour in the lATL which may underlie this distinction. This work was published in Nature Communications (Striem-Amit et al., 2018b).
Strong effects in ATL were not found for tool-use experience in the ULD, where other areas in the occipitotemporal and parietal lobes are implicated in experience of manipulation, showing domain specificity of each system. This work is under preparation for publication.
Furthermore, we studied the dependence of perception and brain organization on sensorimotor experience.
In an fMRI experiment studying responses to tools, we found that despite having no experience in manipulating tools with their hands, the visual cortex of the ULDs contained the typical hand-tool- selectivity overlap seen in controls (Bracci et al., 2012), theorized to arise from the common use of tools and hands. This suggests that one’s own sensorimotor experience is not needed for this region’s development. These results were published in PNAS (Striem-Amit et al., 2017). In another experiment studying manual action perception, findings showed that the decoding of abstract hand actions was possible in the ULD visual cortex regions that process actions in controls, regardless of the motor ability to conduct them. This was published in Cerebral Cortex (Vannuscorps et al., 2018). In conjunction with findings of intact domain selectivity in people born blind (e.g. (Heimler et al., 2015)), these studies extend the notion that brain organization develops in each individual based on innate evolutionary-derived connectivity constraints (Mahon and Caramazza, 2009, 2011), and shows that it develops regardless of their experience in any one modality.
In an investigation of the organization of the early sensory cortices in sensory deprivation, we found that the deaf auditory cortex develops its typical topographic network organization without sensory inputs during development. This supports the role of innate (prenatal) connectivity development as an important factor in brain organization, and suggests the auditory cortex topographic patterns are found even in early sensory loss and in adulthood, potentially enabling rehabilitation beyond developmental critical periods. These results were published in in Scientific Reports ((Striem-Amit et al., 2016) .
In contrast, in the ULD the primary sensorimotor cortex area of the missing hands was responsive to multiple body parts, but mostly to those whose cortical territory is close by. This suggests that when partial input is provided (e.g. from other body parts), the competing input would take over the deprived cortical territory, based on proximity and connectivity principles. This study was published in PNAS (Striem-Amit et al., 2018a).
Overall, the project made new discoveries, contributing to our theoretical understanding of the brain and cognition. It showed that the association sensory and motor cortices organization is independent from one’s own sensory experience, and suggests it develops based on innate evolutionary-derived connectivity constraints. This allows the same brain functions to develop in sensory or motor deprivation and in turn allows for their utilization by various compensatory and rehabilitation approaches. In contrast, early sensory cortices structure reflects topographic connectivity, with a different plasticity profile.
These findings were disseminated in publications, academic conferences, workshops and seminars and in general public media. The project also established a new research line studying congenital hand absence and motor rehabilitation, which may lead to clinical translational advancements in prostheses development.
