Prospective motor control and the origins of intentionality in brainstem integrative mechanisms

Delafield-Butt, Jonathan (2013) Prospective motor control and the origins of intentionality in brainstem integrative mechanisms. In: Perception Action and Learning in Early Development, 2013-11-22.

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Abstract

This paper explores the relation between intentionality and prospective motor control. It reasons the origin of intentionality is evident in simple and basic prospectively controlled actions mediated by brainstem integrative mechanisms apparent in animal as well as in early human movement. It identifies an invariant 'sensorimotor intentionality' inherent in prospective action and presents an hierarchical model of its organisation from its pre-conceptual, pre-reflexive origins in brainstem-mediated action to one imbued with reflexive and conceptual cortical capacities. Animal actions exhibit an efficiency and coherence that necessitate prospective temporal organisation. Each particular action, such as the forward displacement of an arm or a leg, must be controlled with anticipation of momenta generated in movement: too much force and the action will overshoot, too little and the action will be ineffective. Further, prospective control of a particular action must be integrated with the movements, postures, and tensions of all body parts, or the organism will be forced to react to unanticipated forces. Finally, movements require monitoring so they stay on course. These three features characterise a primary sensorimotor intentionality. Simple prospective action is first evident in limb movements of human foetuses circa fourteen weeks gestational age. This is a time before cortex has laminated and cortico-striatal pathways matured, suggesting prospective action organisation is a feature of brainstem, not cortical systems. Further, data from anencephalic children demonstrate preservation of coordinated prospective motor control as well as intact conscious awareness -- a finding in agreement with recent renewed focus on primary brainstem consciousness. Corroborated by studies of surgically decerebrated cats and rats, these data suggest primary sensorimotor intentionality is brainstem-mediated. In development, these simple, single intentional acts become serially organised in development to achieve distal means. An hierarchical model is presented to demonstrate the invariance of sensorimotor intentionality as an organising principle of motor control from its primary pre-reflexive and pre-conceptual type evident in single, simple action units (0.3 ? 1.0 sec. duration) through small projects of serially organised action units to achieve proximal goals (1.5-3.0 sec duration), and finally to larger projects that organise projects to achieve distal and abstract goals (>3 seconds). Altogether, this paper demonstrates an invariant sensorimotor intentionality in action organisation that develops in complexity and prospective reach from its primary brainstem-mediated psychomotor organisation to conceptual and reflexive abstraction enabled by cortex.