During goal-directed movements, the head, eyes and limb are dynamically coordinated so as to look at and reach a given target. This study examined whether changes in eye-head-arm coordination affects Anticipatory Postural Adjustments (APAs) in lower limb muscles when performing an arm reaching movement, toward a target of known position. Standing right-handed subjects (n=10) flexed their shoulder and reached, with the index-fingertip, a target placed in front of them, at shoulders height. Four conditions were studied: 1) steadily looking at the target while reaching (Visually-Guided Reaching); 2) starting with the head flexed watching the floor, then Look and Reach the target; 3) as in 2, but Without Reaching and 4) keeping the head flexed until having reached the target (Blind Reaching). Subjects memorized the target position by performing several reaching movements, until they felt confident. Thereafter, they performed in random order 7 sequences of 15 trials (separated by 5 min of rest): one in Visually-Guided Reaching, one in Without Reaching, one in Blind Reaching, and four in Look and Reach. Recorded variables were: arm and head kinematics, vertical electro-oculogram, EMG from right Anterior Deltoid (prime mover), pectoralis major and biceps brachii, EMG from right and left tibialis anterior and hamstring, forces exerted to the ground. For what concerns Look and Reach movements, two coordination strategies were found: trials in which both the eyes and head movements preceded the arm prime mover activity (Look-First, 35.0±6.5% of total), and trials in which the opposite occurred (Arm-First, 35.5±6.6%). In the remaining trials, which were discarded, the prime mover recruitment followed the head extension but preceded the eye movements, or vice-versa. Data analysis revealed that APAs in leg muscles and forces to the ground were more anticipated in Look-First than in Arm-First, as it was in Visually-Guided than in Blind Reaching (p<0.0005), i.e. when a visual information was searched for or already present before starting the arm movements. The time-lag from Look- to Arm-First was not different from that measured between Visually-Guided and Blind Reaching (46.4±9.9ms vs. 42.5±9.1ms, p>0.6). Moreover, in Without Reaching trials the APAs associated to head extension always lagged the APAs observed in both Look-First and Arm-First conditions. Thus, the head extension alone could not be responsible for these latter effects. In conclusion, according to the chosen strategy, Look and Reach movements are programmed by taking into account the availability of online visual information about target position. In fact, when Looking First, the CNS takes into account that such information will be already available when approaching the target, like in Visually-Guided Reaching; instead, when moving the Arm First, the CNS seems not to rely on such information, like in Blind Reaching. Neither the ocular movements nor the head extension seem to be responsible for the change in APA programming, given the similarity of the Look-First to Arm-First and the Visually-Guided to Blind Reaching time-lags. Thus, considering also the time for cortical processing, it is likely that the expectancy of visual information influences the programming of arm movement.
Anticipatory postural adjustments associated to reaching movements are likely programmed according to the expectancy of visual information
F. Bolzoni;
2015-01-01
Abstract
During goal-directed movements, the head, eyes and limb are dynamically coordinated so as to look at and reach a given target. This study examined whether changes in eye-head-arm coordination affects Anticipatory Postural Adjustments (APAs) in lower limb muscles when performing an arm reaching movement, toward a target of known position. Standing right-handed subjects (n=10) flexed their shoulder and reached, with the index-fingertip, a target placed in front of them, at shoulders height. Four conditions were studied: 1) steadily looking at the target while reaching (Visually-Guided Reaching); 2) starting with the head flexed watching the floor, then Look and Reach the target; 3) as in 2, but Without Reaching and 4) keeping the head flexed until having reached the target (Blind Reaching). Subjects memorized the target position by performing several reaching movements, until they felt confident. Thereafter, they performed in random order 7 sequences of 15 trials (separated by 5 min of rest): one in Visually-Guided Reaching, one in Without Reaching, one in Blind Reaching, and four in Look and Reach. Recorded variables were: arm and head kinematics, vertical electro-oculogram, EMG from right Anterior Deltoid (prime mover), pectoralis major and biceps brachii, EMG from right and left tibialis anterior and hamstring, forces exerted to the ground. For what concerns Look and Reach movements, two coordination strategies were found: trials in which both the eyes and head movements preceded the arm prime mover activity (Look-First, 35.0±6.5% of total), and trials in which the opposite occurred (Arm-First, 35.5±6.6%). In the remaining trials, which were discarded, the prime mover recruitment followed the head extension but preceded the eye movements, or vice-versa. Data analysis revealed that APAs in leg muscles and forces to the ground were more anticipated in Look-First than in Arm-First, as it was in Visually-Guided than in Blind Reaching (p<0.0005), i.e. when a visual information was searched for or already present before starting the arm movements. The time-lag from Look- to Arm-First was not different from that measured between Visually-Guided and Blind Reaching (46.4±9.9ms vs. 42.5±9.1ms, p>0.6). Moreover, in Without Reaching trials the APAs associated to head extension always lagged the APAs observed in both Look-First and Arm-First conditions. Thus, the head extension alone could not be responsible for these latter effects. In conclusion, according to the chosen strategy, Look and Reach movements are programmed by taking into account the availability of online visual information about target position. In fact, when Looking First, the CNS takes into account that such information will be already available when approaching the target, like in Visually-Guided Reaching; instead, when moving the Arm First, the CNS seems not to rely on such information, like in Blind Reaching. Neither the ocular movements nor the head extension seem to be responsible for the change in APA programming, given the similarity of the Look-First to Arm-First and the Visually-Guided to Blind Reaching time-lags. Thus, considering also the time for cortical processing, it is likely that the expectancy of visual information influences the programming of arm movement.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
