Abstract
Predicting the consequences of one’s own movements can be challenging when confronted with completely novel environmental dynamics, such as microgravity in space. The absence of gravitational force disrupts internal models of the central nervous system (CNS) that have been tuned to the dynamics of a constant 1-g environment since birth. In the context of object manipulation, inadequate internal models produce prediction uncertainty evidenced by increases in the grip force (GF) safety margin that ensures a stable grip during unpredicted load perturbations. This margin decreases with practice in a novel environment. However, it is not clear how the CNS might react to a reduced, but non-zero, gravitational field, and if adaptation to reduced gravity might be beneficial for subsequent microgravity exposure. That is, we wondered if a transfer of learning can occur across various reduced-gravity environments. In this study, we investigated the kinematics and dynamics of vertical arm oscillations during parabolic flight maneuvers that simulate Mars gravity, Moon gravity, and microgravity, in that order. While the ratio of and the correlation between GF and load force (LF) evolved progressively with practice in Mars gravity, these parameters stabilized much quicker to subsequently presented Moon and microgravity conditions. These data suggest that prior short-term adaptation to one reduced-gravity field facilitates the CNS’s ability to update its internal model during exposure to other reduced gravity fields.
Highlights
The human central nervous system (CNS) is highly skilled in its ability to model, with great accuracy, the physics underlying bodily interactions with the world
We found no evidence that performing the task in hyper-gravity affected task performance in the subsequent Mars, Moon, or Micro conditions [two-way repeated-measures analysis of variance (ANOVA) with the factors Condition and Preceded by Hyper], with the exception of movement amplitude, which was significantly smaller during these parabolas [F(1,7) = 5.64, p = 0.049]
We found that prior adaptation to Mars gravity quickened subsequent adaptation to Moon and 0-g environments, suggesting that the new internal model developed during exposure to Mars gravity is flexible enough to be adapted rapidly to other novel reduced gravitational fields
Summary
The human central nervous system (CNS) is highly skilled in its ability to model, with great accuracy, the physics underlying bodily interactions with the world. When confronted with a 0-g environment for the first time (in the context of parabolic flights), subjects adopt the opposite strategy: they increase GF relative to that used in 1-g (Augurelle et al, 2003), producing an even greater safety margin. This initial increase in safety margin has been viewed as a strategy to cope with heightened uncertainty, or noise, in one’s ability to predict LF magnitudes (Crevecoeur et al, 2010; Hadjiosif and Smith, 2015). With training in the new gravitational field, the GF and safety margin decrease as subjects adapt to the novel gravitational field (Hermsdörfer et al, 1999; Augurelle et al, 2003)
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