Anticipatory Postural Adjustments associated with reaching movements are programmed according to the availability of visual information

Abstract

During goal-directed arm movements, the eyes, head, and arm are coordinated to look at and reach the target. We examined whether the expectancy of visual information about the target modifies Anticipatory Postural Adjustments (APAs). Ten standing subjects had to (1) move the eyes, head and arm, so as to reach, with both gaze and index-finger, a target of known position placed outside their visual field (Gaze-Reach); (2) look at the target while reaching it (Reach in Full Vision); (3) keep the gaze away until having touched it (Reach then Gaze) and (4) just Gaze without Reach the target. We recorded eye, head, right arm, and acromion kinematics, EMGs from upper- and lower-limb muscles, and forces exerted on the ground. In Gaze-Reach, two coordination strategies were found: when gaze preceded arm muscle recruitment (Gaze-first) and when the opposite occurred (Reach-first). APAs in acromion kinematics, leg muscles, and ground forces started significantly earlier in Gaze-first vs. Reach-first (mean time advance: 44.3 ± 8.9 ms), as it was in Reach in Full Vision vs. Reach then Gaze (39.5 ± 7.9 ms). The Gaze-first to Reach-first time-shift was similar to that between Reach in Full Vision and Reach then Gaze (p = 0.58). Moreover, Gaze without Reach data witnessed that the head-induced postural actions did not affect the APA onset in Gaze-first and Reach-first. In conclusion, in Gaze-first, the central control of posture considers visual information while planning the movement, like in Reach in Full Vision; while Reach-first is more similar to Reach then Gaze, where vision is not required.

Transcranial Direct Current Stimulation on Parietal Operculum Contralateral to the Moving Limb Does Not Affect the Programming of Intra-Limb Anticipatory Postural Adjustments

“…PO is the crucial part, in this multimodal network, where visual, somatosensory and auditory functional streams converge; in turn, PO is connected to motor and premotor areas (Felleman and Van Essen, 1991). In this regard, it is also interesting to note that APAs are influenced by the availability of visual information (Esposti et al, 2017), which may indirectly point out a PO involvement. On these premises, we tested whether the PO contralateral to the moving limb contralateral Parietal Operculum (coPO) is involved in the control of intra-limb APAs associated to index-finger flexion movements.…”

Anticipatory postural adjustments during joint action coordination

“…An oculomotor saccade towards the object ahead of the hand-grasping phase 21 combined with the efferent copy signal of the command to the lifting hand could provide crucial inputs in producing reaching APAs. Indeed, APAs during arm-pointing towards a target from a standing position have been shown to depend on oculomotor timing 22 , a result suggesting that the commands to eye and postural muscles are created at the same time. Without visual cues, flexor deactivation onset was systematically recorded after grasping (referring to grasping APAs), which is when haptic input (from the receptors in muscles, joints and skin) can combine with the efferent copy signal for the coordination of the two hands.…”

Interaction between Feet and Gaze in Postural Control

“…When performing a voluntary movement such as pulling with the hand on a bar attached to a wall, subjects activate the ankle extensor muscles (gastrocnemius) 100 ms before the arm flexors [ 43 ]. Other anticipatory neuromuscular activities have been studied, in particular during leg elevation movements, head rotation [ 46 ]), rotation of the eyes [ 47 ], and even in relation with reflex visceral movements, such as coughing [ 48 ].…”