Visuomotor Adaptation Does Not Recalibrate Kinesthetic Sense of Felt Hand Path

The independence of impairments in proprioception and visuomotor adaptation after stroke

BACKGROUND

Proprioceptive impairments are common after stroke and are associated with worse motor recovery and poor rehabilitation outcomes. Motor learning may also be an important factor in motor recovery, and some evidence in healthy adults suggests that reduced proprioceptive function is associated with reductions in motor learning. It is unclear how impairments in proprioception and motor learning relate after stroke. Here we used robotics and a traditional clinical assessment to examine the link between impairments in proprioception after stroke and a type of motor learning known as visuomotor adaptation.

METHODS

We recruited participants with first-time unilateral stroke and controls matched for overall age and sex. Proprioceptive impairments in the more affected arm were assessed using robotic arm position- (APM) and movement-matching (AMM) tasks. We also assessed proprioceptive impairments using a clinical scale (Thumb Localization Test; TLT). Visuomotor adaptation was assessed using a task that systematically rotated hand cursor feedback during reaching movements (VMR). We quantified how much participants adapted to the disturbance and how many trials they took to adapt to the same levels as controls. Spearman's rho was used to examine the relationship between proprioception, assessed using robotics and the TLT, and visuomotor adaptation. Data from healthy adults were used to identify participants with stroke who were impaired in proprioception and visuomotor adaptation. The independence of impairments in proprioception and adaptation were examined using Fisher's exact tests.

RESULTS

Impairments in proprioception (58.3%) and adaptation (52.1%) were common in participants with stroke (n = 48; 2.10% acute, 70.8% subacute, 27.1% chronic stroke). Performance on the APM task, AMM task, and TLT scores correlated weakly with measures of visuomotor adaptation. Fisher's exact tests demonstrated that impairments in proprioception, assessed using robotics and the TLT, were independent from impairments in visuomotor adaptation in our sample.

CONCLUSION

Our results suggest impairments in proprioception may be independent from impairments in visuomotor adaptation after stroke. Further studies are needed to understand factors that influence the relationship between motor learning, proprioception and other rehabilitation outcomes throughout stroke recovery.

A condition that produces sensory recalibration and abolishes multisensory integration

We examined the influence of extended exposure to a visuomotor rotation, which induces both motor adaptation and sensory recalibration, on (partial) multisensory integration in a cursor-control task. Participants adapted to a 30° (adaptation condition) or 0° (control condition) visuomotor rotation by making center-out movements to remembered targets. In subsequent test trials of sensory integration, they made center-out movements with variable visuomotor rotations and judged the position of hand or cursor at the end of these movements. Test trials were randomly embedded among twice the number of maintenance trials with 30° or 0° rotation. The biases of perceived hand (or cursor) position toward the cursor (or hand) position were measured. We found motor adaptation together with proprioceptive and visual recalibrations in the adaptation condition. Unexpectedly, multisensory integration was absent in both the adaptation and control condition. The absence stemmed from the extensive experience of constant visuomotor rotations of 30° or 0°, which probably produced highly precise predictions of the visual consequences of hand movements. The frequently confirmed predictions then dominated the estimate of the visual movement consequences, leaving no influence of the actual visuomotor rotations in the minority of test trials. Conversely, multisensory integration was present for sensed hand positions when these were indirectly assessed from movement characteristics, indicating that the relative weighting of discrepant estimates of hand position was different for motor control. The existence of a condition that abolishes multisensory integration while keeping sensory recalibration suggests that mechanisms that reduce sensory discrepancies (partly) differ between integration and recalibration.

Long-term retention of proprioceptive recalibration

Sensorimotor changes are well documented following reaches with altered visual feedback of the hand. Specifically, reaches are adapted and proprioceptive estimates of felt hand position shifted in the direction of the visual feedback experienced. While research has examined one's ability to retain reach adaptation, limited attention has been given to the retention of proprioceptive recalibration. This experiment examined retention of proprioceptive recalibration in the form of recall and savings (i.e., faster proprioceptive recalibration on subsequent testing days) over an extended period of time (i.e., four days). As well, we looked to determine the benefits of additional training on short-term retention (i.e., one day) of proprioceptive recalibration. Twenty-four participants trained to reach to a visual target while seeing a cursor that was rotated 30° clockwise relative to their hand on an initial day of testing. Half of the participants then completed additional reach training trials on 4 subsequent testing days (Training group), whereas the second half of participants did not complete additional training until Day 5 (Non-Training group). Participants provided estimates of their felt hand position on all 5 testing days to establish retention of proprioceptive recalibration. Results revealed that proprioceptive recalibration was recalled 24 h after initial training across all participants. Recall of proprioceptive recalibration was not observed on subsequent testing days for the Non-Training group, while recall of proprioceptive recalibration was retained at a similar level across all subsequent testing days for the Training group. Retention of proprioceptive recalibration in the form of savings was observed on Day 5 in the Non-Training group. These results reveal that short-term recall of proprioceptive recalibration does not benefit from additional training. Moreover, the different time scales (i.e., retention in the form of recall seen only at 24 h after initial training versus savings observed 4 days after initial training in the Non-Training group), suggest that distinct processes may underlie recall and savings of proprioceptive recalibration.

Sensorimotor recalibration during split-belt walking: task-specific and multisensory?

Motor adaptations not only recalibrate movement execution but also can lead to altered movement perception in multiple sensory domains. Vazquez, Statton, Busgang, and Bastian (J Neurophysiol 114: 3255-3267, 2015) recently showed that split-belt walking affects perception of leg speed during walking, but not perceptions of leg position during standing and walking or perception of contact force during stepping. Considering their findings within the broader scope of sensorimotor recalibration in other tasks, we suggest that sensorimotor recalibrations are task specific and can be multisensory.

Generalization patterns for reach adaptation and proprioceptive recalibration differ after visuomotor learning

Visuomotor learning results in changes in both motor and sensory systems (Cressman EK, Henriques DY. J Neurophysiol 102: 3505-3518, 2009), such that reaches are adapted and sense of felt hand position recalibrated after reaching with altered visual feedback of the hand. Moreover, visuomotor learning has been shown to generalize such that reach adaptation achieved at a trained target location can influence reaches to novel target directions (Krakauer JW, Pine ZM, Ghilardi MF, Ghez C. J Neurosci 20: 8916-8924, 2000). We looked to determine whether proprioceptive recalibration also generalizes to novel locations. Moreover, we looked to establish the relationship between reach adaptation and changes in sense of felt hand position by determining whether proprioceptive recalibration generalizes to novel targets in a similar manner as reach adaptation. On training trials, subjects reached to a single target with aligned or misaligned cursor-hand feedback, in which the cursor was either rotated or scaled in extent relative to hand movement. After reach training, subjects reached to the training target and novel targets (including targets from a second start position) without visual feedback to assess generalization of reach adaptation. Subjects then performed a proprioceptive estimation task, in which they indicated the position of their hand relative to visual reference markers placed at similar locations as the trained and novel reach targets. Results indicated that shifts in hand position generalized across novel locations, independent of reach adaptation. Thus these distinct sensory and motor generalization patterns suggest that reach adaptation and proprioceptive recalibration arise from independent error signals and that changes in one system cannot guide adjustments in the other.

Assessing Proprioception: A Systematic Review of Possibilities

Proprioception is a vital aspect of motor control and when degraded or lost can have a profound impact on function in diverse clinical populations. This systematic review aimed to identify clinically related tools to measure proprioceptive acuity, to classify the construct(s) underpinning the tools, and to report on the clinimetric properties of the tools. We searched key databases with the pertinent search terms, and from an initial list of 935 articles, we identified 57 of relevance. These articles described 32 different tools or methods to quantify proprioception. There was wide variation in methods, the joints able to be tested, and the populations sampled. The predominant construct was active or passive joint position detection, followed by passive motion detection and motion direction discrimination. The clinimetric properties were mostly poorly evaluated or reported. The Rivermead Assessment of Somatosensory Perception was generally considered to be a valid and reliable tool but with low precision; other tools with higher precision are potentially not clinically feasible. Clinicians and clinical researchers can use the summary tables to make more informed decisions about which tool to use to match their predominant requirements. Further discussion and research is needed to produce measures of proprioception that have improved validity and utility.

Reach adaptation and proprioceptive recalibration following terminal visual feedback of the hand

We have shown that when subjects reach with continuous, misaligned visual feedback of their hand, their reaches are adapted and proprioceptive sense of hand position is recalibrated to partially match the visual feedback (Salomonczyk et al., 2011). It is unclear if similar changes arise after reaching with visual feedback that is provided only at the end of the reach (i.e., terminal feedback), when there are shorter temporal intervals for subjects to experience concurrent visual and proprioceptive feedback. Subjects reached to targets with an aligned hand-cursor that provided visual feedback at the end of each reach movement across a 99-trial training block, and with a rotated cursor over three successive blocks of 99 trials each. After each block, no cursor reaches, to measure aftereffects, and felt hand positions were measured. Felt hand position was determined by having subjects indicate the position of their unseen hand relative to a reference marker. We found that subjects adapted their reaches following training with rotated terminal visual feedback, yet slightly less (i.e., reach aftereffects were smaller), than subjects from a previous study who experienced continuous visual feedback. Nonetheless, current subjects recalibrated their sense of felt hand position in the direction of the altered visual feedback, but this proprioceptive change increased incrementally over the three rotated training blocks. Final proprioceptive recalibration levels were comparable to our previous studies in which subjects performed the same task with continuous visual feedback. Thus, compared to reach training with continuous, but altered visual feedback, subjects who received terminal altered visual feedback of the hand produced significant but smaller reach aftereffects and similar changes in hand proprioception when given extra training. Taken together, results suggest that terminal feedback of the hand is sufficient to drive motor adaptation, and also proprioceptive recalibration.

Body posture modulates imagined arm movements and responds to them

Imagined movements are thought to simulate physical ones, with similar behavioral constraints and neurophysiological activation patterns and with an inhibition mechanism that suppresses movement execution. When upper body movements such as reaching with the arm are made from an upright stance, lower body and trunk muscles are also activated to maintain body posture. It is not clear to what extent parameters of imagined manual movements are sensitive to the postural adjustments their execution would necessitate, nor whether such postural responses are as effectively inhibited as the imagined movements themselves. We asked healthy young participants to imagine reaching movements of the arm while in upright stance, and we measured their self-reported movement times and postural sway during imagined movements. We manipulated mediolateral stance stability and the direction of arm movement (mediolateral or anteroposterior). Imagined arm movements were reportedly slower when subjects were standing in a mediolaterally less stable stance, and the body swayed more when arm movements were imagined in the direction of postural vulnerability. The results suggest that the postural state of the whole body, not just the involved limbs, informs trajectory planning during motor imagery and that measurable adjustments to body posture accompany imagined manual actions. It has been suggested that movement is suppressed during motor imagery by a premotor inhibitory mechanism operating at brain stem or spinal level. Any such inhibition must be incomplete because, for example, it does not eliminate autonomic arousal. Our results suggest that it also does not effectively suppress postural adjustments planned in support of imagined movements.

Saccadic-like visuomotor adaptation involves little if any perceptual effects

Studies on visuomotor adaptation provide crucial clues on the functional properties of the human motor system. The widely studied saccadic adaptation paradigm is a major example of such a fruitful field of investigation. Magescas and Prablanc (J Cogn Neurosci 18(1):75-83, 2006) proposed a transposition of this protocol to arm pointing behavior, by designing an experiment in which the informational context of the upper limb visuomotor system is comparable to that of the saccadic system. Subjects were given terminal only visual feedback in a hand pointing task, assumed to produce a purely terminal visual error signal. Importantly, this paradigm has been shown to induce no saccadic adaptation. Although the saccadic adaptation paradigm is known to induce a predominantly motor adaptation with minor sensory effects, the lack of sensory changes has not been tested in its transposition to pointing. The present study was a partial replication of Magescas and Prablanc's (J Cogn Neurosci 18(1):75-83, 2006) study with additional control tests. A first experiment searched for a possible change in the static visual-to-proprioceptive congruency. A second experiment, based on an anti-pointing task, aimed at separating the sensory and motor effects of the adaptation in a dynamic condition. Consistent with most results on saccadic adaptation, we found a predominant adaptation of the motor components, with little if any involvement of the sensory components. Results are interpreted by proposing a causal relationship between the type of error signal and its adaptive effects.

Proprioceptive recalibration following prolonged training and increasing distortions in visuomotor adaptation

Reaching with misaligned visual feedback of the hand leads to reach adaptation (motor recalibration) and also results in partial sensory recalibration, where proprioceptive estimates of hand position are changed in a way that is consistent with the visual distortion. The goal of the present study was to explore the relationship between changes in sensory and motor systems by examining these processes following (1) prolonged reach training and (2) training with increasing visuomotor distortions. To examine proprioceptive recalibration, we determined the position at which subjects felt their hand was aligned with a reference marker after completing three blocks of reach training trials with a cursor that was rotated 30° clockwise (CW) for all blocks, or with a visuomotor distortion that was increased incrementally across the training blocks up to 70°CW relative to actual hand motion. On average, subjects adapted their reaches by 16° and recalibrated their sense of felt hand position by 7° leftwards following the first block of reach training trials in which they reached with a cursor that was rotated 30°CW relative to the hand, compared to baseline values. There was no change in these values for the 30° training group across subsequent training blocks. However, subjects training with increasing levels of visuomotor distortion showed increased reach adaptation (up to 34° leftward movement aftereffects) and sensory recalibration (up to 15° leftwards). Analysis of motor and sensory changes following each training block did not reveal any significant correlations, suggesting that the processes underlying motor adaptation and proprioceptive recalibration occur simultaneously yet independently of each other.

Motor adaptation and proprioceptive recalibration

Goal-directed reaches are rapidly adapted after reaching with misaligned visual feedback of the hand. It has been suggested that reaching with misaligned visual feedback of the hand also results in proprioceptive recalibration (i.e., realigning proprioceptive estimates of hand position to match visual estimates). In this chapter, we review a series of experiments conducted in our lab which examine this proposal. We assessed proprioceptive recalibration by comparing subjects' estimates of the position at which they felt their hand was aligned with a reference marker (visual or proprioceptive) before and after aiming with a misaligned cursor that was typically rotated 30° clockwise (CW) with respect to the hand. In general, results indicated that subjects recalibrated proprioception such that their estimates of felt hand position were shifted in the same direction that they adapted their reaches. Moreover, proprioception was recalibrated to a similar extent of motor adaptation (∼30%), regardless of how the hand was positioned during the estimate trials (active or passive placement), the location or modality of the reference marker (visual or proprioceptive), the hand used during reach training (right or left), how the distortion was introduced (gradual or abrupt), and age (young or older subjects) and the magnitude of the visuomotor distortion introduced (30° or 50° or 70°). These results suggest that in addition to recalibrating the sensorimotor transformations underlying reaching movements, visuomotor adaptation results in partial proprioceptive recalibration.

The adaptability of self-action perception and movement control when the limb is passively versus actively moved

Research suggests that perceptual experience of our movements adapts together with movement control when we are the agents of our actions. Is this agency critical for perceptual and motor adaptation? We had participants view cursor feedback during elbow extension-flexion movements when they (1) actively moved their arm, or (2) had their arm passively moved. We probed adaptation of movement perception by having participants report the reversal point of their unseen movement. We probed adaptation of movement control by having them aim to a target. Perception and control of active movement were influenced by both types of exposure, although adaptation was stronger following active exposure. Furthermore, both types of exposure led to a change in the perception of passive movements. Our findings support the notion that perception and control adapt together, and they suggest that some adaptation is due to recalibrated proprioception that arises independently of active engagement with the environment.

The impact of augmented information on visuo-motor adaptation in younger and older adults

Background

Adjustment to a visuo-motor rotation is known to be affected by ageing. According to previous studies, the age-related differences primarily pertain to the use of strategic corrections and the generation of explicit knowledge on which strategic corrections are based, whereas the acquisition of an (implicit) internal model of the novel visuo-motor transformation is unaffected. The present study aimed to assess the impact of augmented information on the age-related variation of visuo-motor adjustments.

Methodology/Principal Findings

Participants performed aiming movements controlling a cursor on a computer screen. Visual feedback of direction of cursor motion was rotated 75° relative to the direction of hand motion. Participants had to adjust to this rotation in the presence and absence of an additional hand-movement target that explicitly depicted the input-output relations of the visuo-motor transformation. An extensive set of tests was employed in order to disentangle the contributions of different processes to visuo-motor adjustment. Results show that the augmented information failed to affect the age-related variations of explicit knowledge, adaptive shifts, and aftereffects in a substantial way, whereas it clearly affected initial direction errors during practice and proprioceptive realignment.

Conclusions

Contrary to expectations, older participants apparently made no use of the augmented information, whereas younger participants used the additional movement target to reduce initial direction errors early during practice. However, after a first block of trials errors increased, indicating a neglect of the augmented information, and only slowly declined thereafter. A hypothetical dual-task account of these findings is discussed. The use of the augmented information also led to a selective impairment of proprioceptive realignment in the younger group. The mere finding of proprioceptive realignment in adaptation to a visuo-motor rotation in a computer-controlled setup is noteworthy since visual and proprioceptive information pertain to different objects.

Visual, motor and attentional influences on proprioceptive contributions to perception of hand path rectilinearity during reaching

We examined how proprioceptive contributions to perception of hand path straightness are influenced by visual, motor and attentional sources of performance variability during horizontal planar reaching. Subjects held the handle of a robot that constrained goal-directed movements of the hand to the paths of controlled curvature. Subjects attempted to detect the presence of hand path curvature during both active (subject driven) and passive (robot driven) movements that either required active muscle force production or not. Subjects were less able to discriminate curved from straight paths when actively reaching for a target versus when the robot moved their hand through the same curved paths. This effect was especially evident during robot-driven movements requiring concurrent activation of lengthening but not shortening muscles. Subjects were less likely to report curvature and were more variable in reporting when movements appeared straight in a novel "visual channel" condition previously shown to block adaptive updating of motor commands in response to deviations from a straight-line hand path. Similarly, compromised performance was obtained when subjects simultaneously performed a distracting secondary task (key pressing with the contralateral hand). The effects compounded when these last two treatments were combined. It is concluded that environmental, intrinsic and attentional factors all impact the ability to detect deviations from a rectilinear hand path during goal-directed movement by decreasing proprioceptive contributions to limb state estimation. In contrast, response variability increased only in experimental conditions thought to impose additional attentional demands on the observer. Implications of these results for perception and other sensorimotor behaviors are discussed.

Reach Adaptation and Proprioceptive Recalibration Following Exposure to Misaligned Sensory Input

Motor adaptation in response to a visuomotor distortion arises when the usual motor command no longer results in the predicted sensory output. In this study, we examined if exposure to a sensory discrepancy was sufficient on its own to produce changes in reaches and recalibrate the sense of felt hand position in the absence of any voluntary movements. Subjects pushed their hand out along a robot-generated fixed linear path (active exposure group) or were passively moved along the same path (passive exposure group). This fixed path was gradually rotated counterclockwise around the home position with respect to the path of the cursor. On all trials, subjects saw the cursor head directly to the remembered target position while their hand moved outwards. We found that after exposure to the visually distorted hand motion, subjects in both groups adapted their reaches such that they aimed ∼6° to the left of the intended target. The magnitude of reach adaptation was similar to the extent that subjects recalibrated their sense of felt hand position. Specifically the position at which subjects perceived their unseen hand to be aligned with a reference marker was the same as that to which they reached when allowed to move freely. Given the similarity in magnitude of these adaptive responses we propose that reach adaptation arose due to changes in subjects' sense of felt hand position. Moreover, results indicate that motor adaptation can arise following exposure to a sensory mismatch in the absence of movement related error signals.

Sensory Recalibration of Hand Position Following Visuomotor Adaptation

Goal-directed reaches are rapidly adapted following exposure to misaligned visual feedback of the hand. It has been suggested that these changes in reaches result in sensory recalibration (i.e., realigning proprioceptive estimates of hand position to match the visual estimates). In the current study we tested whether visuomotor adaptation results in recalibration of hand proprioception by comparing subjects' estimates of the position at which they felt their hand was aligned with a reference marker (visual or proprioceptive) before and after aiming with a misaligned cursor. The misaligned cursor was either translated or rotated to the right of the actual hand location. On the estimation trials, we did not allow subjects to freely move their hands into position. Instead, a robot manipulandum either passively positioned the hand ( experiments 1 and 2) or subjects moved their hand along a robot-generated constrained pathway ( experiments 3 and 4). We found that regardless of experimental manipulation, subjects' proprioceptive estimates of hand position were more biased to the left after visuomotor adaptation. The leftward shift in subjects' estimates was in the same direction and one third of the magnitude of the adapted movement. This suggests that in addition to recalibrating the sensorimotor transformations underlying reaching movements, visuomotor adaptation results in partial proprioceptive recalibration.