Acceleration and Velocity Dissociate Temporal Phases of Postural Control in Rhesus Macaques

Maintaining balance requires the nervous system to transform sensory signals about unexpected postural perturbations into precisely timed motor commands. Although human studies have established that postural responses unfold in distinct temporal phases, how specific kinematic variables structure these phases during rotational perturbations remains unresolved, because angular acceleration and velocity are typically confounded. Here, we developed a rhesus macaque model of postural control that independently manipulates angular acceleration and peak velocity during transient pitch and roll tilts in monkeys of either sex. By simultaneously measuring head kinematics (directly relevant to vestibular signaling) and center-of-pressure dynamics, we quantified how sensory inputs and motor outputs evolve across successive phases of the postural response. We show that short-latency postural responses (<100 ms) are primarily governed by angular acceleration, whereas medium-latency responses (100-200 ms) scale with angular velocity. This dissociation was robust across perturbation axes and accompanied by axis-dependent control strategies: roll tilts elicited constrained head motion consistent with active stabilization in space, whereas pitch tilts produced more compliant, platform-following behavior. Together, these findings identify distinct kinematic variables governing successive phases of balance control and establish a primate framework for linking neural circuit activity to the temporal organization of postural responses.