The detection of human finger movement is not facilitated by input from receptors in adjacent digits

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.

Proprioceptive sensitivity to imposed finger deflections

Hand proprioception, the sense of the posture and movements of the wrist and digits, is critical to dexterous manual behavior and to stereognosis, the ability to sense the three-dimensional structure of objects held in the hand. To better understand this sensory modality and its role in hand function, we sought to characterize the acuity with which the postures and movements of finger joints are sensed. To this end, we measured the ability of human subjects to discriminate changes in posture and speed around the three joints of the index finger. In these experiments, we isolated the sensory component by imposing the postures on an otherwise still hand, to complement other studies in which subjects made judgments on actively achieved postures. We found that subjects could reliably sense 12-16% changes in joint angle and 18-32% changes in joint speed. Furthermore, the acuity for posture and speed was comparable across the three joints of the finger. Finally, task performance was unaffected by the presence of a vibratory stimulus, calling into question the role of cutaneous cues in hand proprioception.NEW & NOTEWORTHY Manual dexterity and stereognosis are supported by two exquisite sensory systems, namely touch and proprioception. Here, we measure the sensitivity of hand proprioception and show that humans can sense the posture and movements of the fingers with great accuracy. We also show that application of a skin vibration does not impair sensitivity, suggesting that proprioceptive acuity relies primarily on receptors in the muscles (and possibly tendons) rather than the skin.

Upper Extremity Proprioception After Stroke: Bridging the Gap Between Neuroscience and Rehabilitation

Proprioception is an important aspect of function that is often impaired in the upper extremity following stroke. Unfortunately, neurorehabilitation has few evidence based treatment options for those with proprioceptive deficits. The authors consider potential reasons for this disparity. In doing so, typical assessments and proprioceptive intervention studies are discussed. Relevant evidence from the field of neuroscience is examined. Such evidence may be used to guide the development of targeted interventions for upper extremity proprioceptive deficits after stroke. As researchers become more aware of the impact of proprioceptive deficits on upper extremity motor performance after stroke, it is imperative to find successful rehabilitation interventions to target these deficits and ultimately improve daily function.

Vibrotactile stimulation of fast-adapting cutaneous afferents from the foot modulates proprioception at the ankle joint

It has previously been shown that cutaneous sensory input from across a broad region of skin can influence proprioception at joints of the hand. The present experiment tested whether cutaneous input from different skin regions across the foot can influence proprioception at the ankle joint. The ability to passively match ankle joint position (17° and 7° plantar flexion and 7° dorsiflexion) was measured while cutaneous vibration was applied to the sole (heel, distal metatarsals) or dorsum of the target foot. Vibration was applied at two different frequencies to preferentially activate Meissner's corpuscles (45 Hz, 80 μm) or Pacinian corpuscles (255 Hz, 10 μm) at amplitudes ∼3 dB above mean perceptual thresholds. Results indicated that cutaneous input from all skin regions across the foot could influence joint-matching error and variability, although the strongest effects were observed with heel vibration. Furthermore, the influence of cutaneous input from each region was modulated by joint angle; in general, vibration had a limited effect on matching in dorsiflexion compared with matching in plantar flexion. Unlike previous results in the upper limb, we found no evidence that Pacinian input exerted a stronger influence on proprioception compared with Meissner input. Findings from this study suggest that fast-adapting cutaneous input from the foot modulates proprioception at the ankle joint in a passive joint-matching task. These results indicate that there is interplay between tactile and proprioceptive signals originating from the foot and ankle.

Systematic changes in position sense accompany normal aging across adulthood

Background

Development of clinical neurological assessments aimed at separating normal from abnormal capabilities requires a comprehensive understanding of how basic neurological functions change (or do not change) with increasing age across adulthood. In the case of proprioception, the research literature has failed to conclusively determine whether or not position sense in the upper limb deteriorates in elderly individuals. The present study was conducted a) to quantify whether upper limb position sense deteriorates with increasing age, and b) to generate a set of normative data that can be used for future comparisons with clinical populations.

Methods

We examined position sense in 209 healthy males and females between the ages of 18 and 90 using a robotic arm position-matching task that is both objective and reliable. In this task, the robot moved an arm to one of nine positions and subjects attempted to mirror-match that position with the opposite limb. Measures of position sense were recorded by the robotic apparatus in hand-and joint-based coordinates, and linear regressions were used to quantify age-related changes and percentile boundaries of normal behaviour. For clinical comparisons, we also examined influences of sex (male versus female) and test-hand (dominant versus non-dominant) on all measures of position sense.

Results

Analyses of hand-based parameters identified several measures of position sense (Variability, Shift, Spatial Contraction, Absolute Error) with significant effects of age, sex, and test-hand. Joint-based parameters at the shoulder (Absolute Error) and elbow (Variability, Shift, Absolute Error) also exhibited significant effects of age and test-hand.

Conclusions

The present study provides strong evidence that several measures of upper extremity position sense exhibit declines with age. Furthermore, this data provides a basis for quantifying when changes in position sense are related to normal aging or alternatively, pathology.

Local subcutaneous and muscle pain impairs detection of passive movements at the human thumb

Activity in both muscle spindle endings and cutaneous stretch receptors contributes to the sensation of joint movement. The present experiments assessed whether muscle pain and subcutaneous pain distort proprioception in humans. The ability to detect the direction of passive movements at the interphalangeal joint of the thumb was measured when pain was induced experimentally in four sites: the flexor pollicis longus (FPL), the subcutaneous tissue overlying this muscle, the flexor carpi radialis (FCR) muscle and the subcutaneous tissue distal to the metacarpophalangeal joint of thumb. Tests were conducted when pain was at a similar subjective intensity. There was no significant difference in the ability to detect flexion or extension under any painful or non-painful condition. The detection of movement was significantly impaired when pain was induced in the FPL muscle, but pain in the FCR, a nearby muscle that does not act on the thumb, had no effect. Subcutaneous pain also significantly impaired movement detection when initiated in skin overlying the thumb, but not in skin overlying the FPL muscle in the forearm. These findings suggest that while both muscle and skin pain can disturb the detection of the direction of movement, the impairment is site-specific and involves regions and tissues that have a proprioceptive role at the joint. Also, pain induced in FPL did not significantly increase the perceived size of the thumb. Proprioceptive mechanisms signalling perceived body size are less disturbed by a relevant muscle nociceptive input than those subserving movement detection. The results highlight the complex relationship between nociceptive inputs and their influence on proprioception and motor control.

Impairment of human proprioception by high-frequency cutaneous vibration

These experiments assessed whether the impairment in proprioceptive acuity in the hand during 'interfering' cutaneous stimulation could be caused by inputs from Pacinian corpuscles. The ability to detect passive movements at the proximal interphalangeal joint of the index finger was measured when vibrotactile stimuli were applied to the adjacent middle finger and thenar eminence at frequencies and amplitudes that favour activation of rapidly adapting cutaneous afferents. Inputs from Pacinian corpuscles are favoured with high-frequency vibration (300 Hz), while those from Meissner corpuscles are favoured by lower frequencies (30 Hz). Detection of movement was significantly impaired when 300 Hz (20 microm peak-to-peak amplitude) complex vibration or 300 Hz (50 microm) sinusoidal vibration was applied to the middle finger and thenar eminence. In contrast, detection of movements was not altered by low-frequency sinusoidal vibration at 30 Hz with an amplitude of 50 microm or with a larger amplitude matched in subjective intensity to the 300 Hz sinusoidal stimulus. Thus it is unlikely that the impairment in detection was due to attention being diverted by vibration of an adjacent digit. In addition, an increase in amplitude of 300 Hz vibration led to a greater impairment of movement detection, so that the impairment was graded with the input. The time taken to nominate the direction of applied movement also increased during 300 Hz but not during 30 Hz sinusoidal vibration. These findings suggest that stimuli which preferentially activate Pacinian, but not Meissner corpuscles, impair proprioceptive acuity in a movement detection task.

Cutaneous afferents provide a neuronal population vector that encodes the orientation of human ankle movements

The aim of this study was to analyse the directional coding of two-dimensional limb movements by cutaneous afferents from skin areas covering a multidirectional joint, the ankle. The activity of 89 cutaneous afferents was recorded in the common peroneal nerve, and the mean discharge frequency of each unit was measured during the outward phase of ramp and hold movements imposed in 16 different directions. Forty-two afferents responded to the movements in the following decreasing order (SA2, n = 24/27; FA2, n = 13/17; FA1, n = 3/24; SA1, n = 2/21). All the units activated responded to a specific range of directions, defining their 'preferred sector', within which their response peaked in a given direction, their 'preferred direction'. Based on the distribution of the preferred directions, two populations of afferents, and hence two skin areas were defined: the anterior and the external lateral parts of the leg. As the directional tuning of each population was cosine shaped, the neuronal population vector model was applied and found to efficiently describe the movement direction encoded by cutaneous afferents, as it has been previously reported for muscle afferents. The responses of cutaneous afferents were then considered with respect to those of the afferents from the underlying muscles, which were previously investigated, and an almost perfect matching of directional sensitivity was observed. It is suggested that the common movement-encoding characteristics exhibited by cutaneous and muscle afferents, as early as the peripheral level, may facilitate the central co-processing of their feedbacks subserving kinaesthesia.

Cutaneous Receptors Contribute to Kinesthesia at the Index Finger, Elbow, and Knee

The neural mechanisms underlying the sense of joint position and movement remain controversial. While cutaneous receptors are known to contribute to kinesthesia for the fingers, the present experiments test the hypothesis that they contribute at other major joints. Illusory movements were evoked at the interphalangeal (IP) joints of the index finger, the elbow, and the knee by stimulation of populations of cutaneous and muscle spindle receptors, both separately and together. Subjects matched perceived movements with voluntary movements of homologous joints on the contralateral side. Cutaneous receptors were activated by stretch of the skin (using 2 intensities of stretch) and vibration activated muscle spindle receptors. Stimuli were designed to activate receptors that discharge during joint flexion. For the index finger, vibration was applied over the extensor tendons on the dorsum of the hand, to evoke illusory metacarpophalangeal (MCP) joint flexion, and skin stretch was delivered around the IP joints. The strong skin stretch evoked the illusion of flexion of the proximal IP joint in 6/8 subjects (12 ± 5°, mean ± SE). For the group, strong skin stretch delivered during vibration increased the perceived flexion of the proximal IP joint by eight times with a concomitant decrease in perceived flexion of the MCP joint compared with vibration alone ( P < 0.05). For the elbow, vibration was applied over the distal tendon of triceps brachii and skin stretch over the dorsal forearm. When delivered alone, strong skin stretch evoked illusory elbow flexion in 5/10 subjects (9 ± 4°). Simultaneous strong skin stretch and vibration increased the illusory elbow flexion for the group by 1.5 times compared with vibration ( P < 0.05). For the knee, vibration was applied over the patellar tendon and skin stretch over the thigh. Skin stretch alone evoked illusory knee flexion in 3/10 subjects (8 ± 4°) and when delivered during vibration, perceived knee flexion increased for the group by 1.4 times compared with vibration ( P < 0.05). Hence inputs from cutaneous receptors, muscle receptors, and combined inputs from both receptors likely subserve kinesthesia at joints throughout the body.