Leia B. Bagesteiro

Differential influence of vision and proprioception on control of movement distance

The purpose of this study was to investigate the contribution of proprioceptive and visual information about initial limb position in controlling the distance of rapid, single-joint reaching movements. Using a virtual reality environment, we systematically changed the relationship between actual and visually displayed hand position as subjects’ positioned a cursor within a start circle. No visual feedback was given during the movement. Subjects reached two visual targets (115 and 125° elbow angle) from four start locations (90, 95, 100, and 105° elbow angle) under four mismatch conditions (0, 5, 10, or 15°). A 2×4×4 ANOVA enabled us to ask whether the subjects controlled the movement distance in accord with the virtual, or the actual hand location. Our results indicate that the movement distance was mainly controlled according to the virtual start location. Whereas distance modification was most extensive for the closer target, analysis of acceleration profiles revealed that, regardless of target position, visual information about start location determined the initial peak in tangential hand acceleration. Peak acceleration scaled with peak velocity and movement distance, a phenomenon termed “pulse-height” control. In contrast, proprioceptive information about actual hand location determined the duration of acceleration, which also scaled with peak velocity and movement distance, a phenomenon termed “pulse-width” control. Because pulse-height and pulse-width mechanisms reflect movement planning and sensory-based corrective processes, respectively, our current findings indicate that vision is used primarily for planning movement distance, while proprioception is used primarily for online corrections during rapid, unseen movements toward visual targets.

Interlimb transfer of load compensation during rapid elbow joint movements

Previous research has shown that training of a novel task can improve subsequent performance in the opposite arm owing to anticipation of the previously learned task conditions. Interestingly, we recently reported preliminary evidence that such transfer might also include modulation of feedback-mediated responses. We now test interlimb transfer of load compensation responses, measured through kinematic and EMG recordings during rapid 20° elbow flexion movements. Two subject groups, LR and RL, each comprising six right-handed subjects, first performed using either the left (LR) or right (RL) arm, followed by opposite arm performance. After 30 trials of consistent performance, five random trials within a background of 50 trials were loaded with a 2-kg mass prior to the “go” signal. We compared load compensation responses for naïve performance with those following opposite arm exposure. Under naïve conditions, the resulting load compensation responses began about 50 ms following movement onset, and were substantially more effective for the nondominant arm. Opposite arm exposure substantially improved the accuracy of only dominant arm responses. This, however, did not occur through changes in the short latency components of the load compensation response. Instead, changes in muscle activities, associated with interlimb transfer, began some 150 ms following movement onset. We expect that these changes represent transfer in the “volitional” component of the load compensation response. Because the shorter latency response was unaffected by opposite arm exposure, modulation of this component likely requires prior experience with limb specific effectors.

Gait characteristics of younger-old and older-old adults walking overground and on a compliant surface

BACKGROUND Walking across unstable surfaces disturbs normal stability and efficient strategies must be used to avoid falls. This study identified age-related changes in gait during unstable surface walking. METHOD Eight healthy younger-old adults (YOG, mean age, 68.6 years) and eight healthy older-old adults (OOG, mean age, 82.1 years) were assessed. Both groups performed the Timed Up and Go Test (TUG) and walked on a rigid and on a compliant surface while kinematic data were obtained. RESULTS The OOG needed more time to complete the TUG test compared to YOG (F1,14=5.18; p=0.04). The gait speed, stride length and vertical displacement of the foot were similar for both groups, but they were slower (F1,14=5.64; p=0.03) when walking on the compliant surface. The knee and hip range of motion on the sagittal plane (F1,14=191.9; p<0.001 and F1,14=36.4, p<0,001, respectively) increased on the complaint surface but no group effect was found. The displacement of upper trunk on the frontal plane was similar between groups (F1,14=2.43; p=0.14) and conditions (F1,14=1.15; p=0.3). The OOG had greater displacement of the pelvic segment on the frontal plane than the YOG (F1,14=4.9; p=0.04) mainly for the complaint surface. CONCLUSIONS Older-old individuals have slower TUG test and greater displacement of the pelvic segment on a compliant surface. More challenging tasks and/or environment should be used for gait assessment and intervention of older adults with risk of falls.

Interlimb transfer of load compensation during single-joint movements

Previous studies have investigated interlimb transfer of adaptation to visuomotor rotations, viscous curl-fields, as well as for ball catching and other complex tasks. We have recently revealed a nondominant arm advantage for load compensation responses. We now examine whether this short-latency response can be modified by prior opposite arm experience. Two subject groups, LR and RL, each comprising six right-handed subjects, experienced unpredictable loading during single joint speed constrained 20/spl deg/elbow flexion. Each group first performed using either the left (LR) or right (RL) arm, followed by opposite arm performance. In order to assess transfer, we compared the same side arm movements (either right or left) following opposite arm performance to those made prior to opposite arm performance (Nai/spl uml/ve). Our preliminary results indicate interlimb transfer, only from the nondominant to the dominant arm. Under nai/spl uml/ve conditions, nondominant arm responses are substantially more efficient, which may preclude improvement and thus limit the effects of opposite arm training. These results indicate that feedforward modifications of feedback based responses can transfer across the limbs, and thus, that such adjustments are not effector-specific.