The long developmental trajectory of body representation plasticity following tool use

Abstract

Humans evolution is distinctly characterized by their exquisite mastery of tools, allowing them to shape their environment in more elaborate ways compared to other species. This ability is present ever since infancy and most theories indicate that children become proficient with tool use very early. In adults, tool use has been shown to plastically modify metric aspects of the arm representation, as indexed by changes in movement kinematics. To date, whether and when the plastic capability of updating the body representation develops during childhood remains unknown. This question is particularly important since body representation plasticity could be impacted by the fact that the human body takes years to achieve a stable metric configuration. Here we assessed the kinematics of 90 young participants (8–21 years old) required to reach for an object before and after tool use, as a function of their pubertal development. Results revealed that tool incorporation, as indexed by the adult typical kinematic pattern, develops very slowly and displays a u-shaped developmental trajectory. From early to mid puberty, the changes in kinematics following tool use seem to reflect a shortened arm representation, opposite to what was previously reported in adults. This pattern starts reversing after mid puberty, which is characterized by the lack of any kinematics change following tool use. The typical adult-like pattern emerges only at late puberty, when body size is stable. These findings reveal the complex dynamics of tool incorporation across development, possibly indexing the transition from a vision-based to a proprioception-based body representation plasticity.

Body schema plasticity is altered in Developmental Coordination Disorder

“…While, to the best of our knowledge, there is no previous investigation of the body image in DCD, we anticipated that it would be preserved (as it is not linked to motor control). Thus, their perceived forearm length should be shorter after tool use, as recently observed in TD children (Martel et al, 2021).…”

“…This suggests that DCD children and early adolescents were able to use visual and/or proprioceptive feedback and compare it with the predicted one/s. As using a tool is thought to require the building of new sensorimotor associations during development (Ganesh et al, 2014;Martel et al, 2021), it is likely that the predicted feedback were initially imprecise and that participants relied on the more trustable information, that is their feedback (Limanowski & Friston, 2020a, 2020b. Their performance suggests they took error signals into account to improve ensuing movements by updating their internal models, to a similar extent their TD peers did.…”

“…By including only the children and early adolescents with DCD scoring between 5 and 13/20, we minimized the potential role of puberty, and focused on a period where the pattern of results in TD participants is rather stable. This led to a final sample of 17 DCD participants, who were compared to a subsample of a larger cohort of TD participants from a previous study (Martel et al, 2021). The two groups were matched for daily tool practice, age, sex and puberty (see Table 2).…”

“…Participants between 123 and 146 cm of height used a 32 cm long tool (DCD group: 4/17; TD group: 5/17). The remaining participants were taller than 147 cm and used a tool of 40 cm long, which is the original length also used for adults (Baccarini et al, 2014;Cardinali et al, 2009Cardinali et al, , 2011Martel et al, 2019Martel et al, , 2021, but 100g lighter to prevent fatigue. Participants' height was collected before the experiment, the lengths of their arm and forearm were measured afterwards.…”

“…Reduction in arm length estimate may result from the need to build new sensorimotor associations for a tool that has never been used before (Ganesh et al, 2014) or from a stronger reliance on visual as compared to proprioceptive guidance in TD children, compared to adults (Martel et al, 2021). Besides, investigating the plasticity of the body estimate in DCD may offer complementary insights to better understand its aetiology (Martel et al, 2017(Martel et al, , 2019(Martel et al, , 2021Medendorp & Heed, 2019). Surprisingly, the role potentially played by an altered body state estimation in DCD's motor deficits has yet been scarcely investigated (Gomez & Sirigu, 2015), although it has been linked indirectly with them.…”