Vannuscorps, G., Wurm, M. F., Striem-Amit, E., & Caramazza, A. (2018).
Large-scale organizations of the hand action observation network in individuals born without hands.
Cerebral Cortex.
AbstractThe human high-level visual cortex comprises regions specialized for the processing of distinct types of stimuli, such as objects, animals, and human actions. How does this specialization emerge? Here, we investigated the role of effector-specific visuomotor coupling experience in shaping the organization of the action observation network (AON) as a window on this question. Observed body movements are frequently coupled with corresponding motor codes, e.g., during monitoring one’s own movements and imitation, resulting in bidirectionally connected circuits between areas involved in body movements observation (e.g., of the hand) and the motor codes involved in their execution. If the organization of the AON is shaped by this effector-specific visuomotor coupling, then, it should not form for body movements that do not belong to individuals’ motor repertoire. To test this prediction, we used fMRI to investigate the spatial arrangement and functional properties of the hand and foot action observation circuits in individuals born without upper limbs. Multivoxel pattern decoding, pattern similarity, and univariate analyses revealed an intact hand AON in the individuals born without upper limbs. This suggests that the organization of the AON does not require effector-specific visuomotor coupling.
Striem-Amit, E., Vannuscorps, G., & Caramazza, A. (2018).
Plasticity based on compensatory effector use in the association but not primary sensorimotor cortex of people born without hands.
Proceedings of the National Academy of Sciences ,
115 (30), 7801-7806.
AbstractWhat forces direct brain organization and its plasticity? When brain regions are deprived of their input, which regions reorganize based on compensation for the disability and experience, and which regions show topographically constrained plasticity? People born without hands activate their primary sensorimotor hand region while moving body parts used to compensate for this disability (e.g., their feet). This was taken to suggest a neural organization based on functions, such as performing manual-like dexterous actions, rather than on body parts, in primary sensorimotor cortex. We tested the selectivity for the compensatory body parts in the primary and association sensorimotor cortex of people born without hands (dysplasic individuals). Despite clear compensatory foot use, the primary sensorimotor hand area in the dysplasic subjects showed preference for adjacent body parts that are not compensatorily used as effectors. This suggests that function-based organization, proposed for congenital blindness and deafness, does not apply to the primary sensorimotor cortex deprivation in dysplasia. These findings stress the roles of neuroanatomical constraints like topographical proximity and connectivity in determining the functional development of primary cortex even in extreme, congenital deprivation. In contrast, increased and selective foot movement preference was found in dysplasics’ association cortex in the inferior parietal lobule. This suggests that the typical motor selectivity of this region for manual actions may correspond to high-level action representations that are effector-invariant. These findings reveal limitations to compensatory plasticity and experience in modifying brain organization of early topographical cortex compared with association cortices driven by function-based organization.
Bracci, S., Caramazza, A., & Peelen, M. V. (2018).
View-invariant representation of hand postures in the human lateral occipitotemporal cortex.
NeuroImage ,
181, 446-452.
AbstractUnderstanding other people's actions and
mental states includes the interpretation of body
postures and movements. In particular, hand postures are an important channel to signal both action and communicative intentions. Recognizing hand postures is computationally challenging because hand postures often differ only in the subtle configuration of relative finger positions and because visual characteristics of hand postures change across viewpoints. To allow for accurate interpretation, the brain needs to represent hand postures in a view-invariant but posture-specific manner. Here we test for such representations in hand-, body-, and object-selective regions of the lateral occipitotemporal cortex (LOTC). We used multivariate
pattern analysis of fMRI data to test for view-specific and view-invariant representations of individual hand postures, separately for two domains: action-related postures (e.g., a precision grasp) and communicative postures (e.g., thumbs up). Results showed that hand-selective LOTC, but not nearby body- and object-selective LOTC, represented hand postures in a view-invariant manner, with relatively similar activity patterns to the same hand posture seen from different viewpoints. View invariance was equally strong for action and communicative postures. By contrast, object-selective cortex represented hand postures in a view-specific manner. These results indicate a role for hand-selective LOTC in solving the view-invariance problem for individual hand postures. View-invariant representations of hand postures in this region may then be accessed and further interpreted by multiple downstream systems to inform high-level judgments related to action understanding, emotion recognition, and non-verbal communication.