What is balance? A vital mechano-regulation paradigm

Abstract

Within minutes of birth a newborn gnu or giraffe works to stand and walk, asserting postural balance and organised animate behaviour in an apparently goal-directed manner. In contrast, robots learning to stand and walk from scratch begin with random flailing, the behaviour cohering over time as the robot internalises some reward or value signal. How does the newborn gnu innately know what goal to aim for, and decide to work towards it? How could similar goal-directed balance learning be implemented in robots? Currently, animate balance inherits its axiomatic definition from the Newtonian formulation for inanimate balance - static mechanical equilibrium. This is arguably inappropriate for animate balance, because animals need to move and are never in static mechanical equilibrium, giving rise to the posture-movement paradox. The present perspective article proposes a more fluid, dynamical axiomatic task definition and goal which (a) isolates resisting gravity, (b) admits and enables movement, and (c) subsumes static mechanical equilibrium as a special case. This novel definition is founded upon inevitable biophysical requirements and observable developmental process. The article explains how animals apprehend and embed this goal through prenatal development suspended in equidense amniotic fluid, and then are challenged to self-maintain it by the perinatal transition. The account entails a paradigmatic shift in putative physiological organisation and associated conceptual framework for balance from a subsidiary sensorimotor control task, to a vital mechano-regulation task organisationally akin to thermo-regulation. This vital mechano-regulation model of balance has practical implications and implies a range of predictions.