Dissociation between dreams and wakefulness: Insights from body and action representations of rare individuals with massive somatosensory deafferentation.

The realism of body and actions in dreams is thought to be induced by simulations based on internal representations used during wakefulness. As somatosensory signals contribute to the updating of body and action representations, these are impaired when somatosensory signals are lacking. Here, we tested the hypothesis that individuals with somatosensory deafferentation have impaired body and actions in their dreams, as in wakefulness. We questioned three individuals with a severe, acquired sensory neuropathy on their dreams. While deafferented participants were impaired in daily life, they could dream of themselves as able-bodied, with some sensations (touch, proprioception) and actions (such as running or jumping) which had not been experienced in physical life since deafferentation. We speculate that simulation in dreams could be based on former, "healthy" body and action representations. Our findings are consistent with the idea that distinct body and action representations may be used during dreams and wakefulness.

The role of somatosensation in automatic visuo-motor control: a comparison of congenital and acquired sensory loss.

Studies of chronically deafferented participants have illuminated how regaining some motor control after adult-onset loss of proprioceptive and touch input depends heavily on cognitive control. In this study we contrasted the performance of one such man, IW, with KS, a woman born without any somatosensory fibres. We postulated that her life-long absence of proprioception and touch might have allowed her to automate some simple visually-guided actions, something IW appears unable to achieve. We tested these two, and two age-matched control groups, on writing and drawing tasks performed with and without an audio-verbal echoing task that added a cognitive demand. In common with other studies of skilled action, the dual task was shown to affect visuo-motor performance in controls, with less well-controlled drawing and writing, evident as increases in path speed and reduction in curvature and trial duration. We found little evidence that IW was able to automate even the simplest drawing tasks and no evidence for automaticity in his writing. In contrast, KS showed a selective increase in speed of signature writing under the dual-task conditions, suggesting some ability to automate her most familiar writing. We also tested tracing of templates under mirror-reversed conditions, a task that imposes a powerful cognitive planning challenge. Both IW and KS showed evidence of a visuo-motor planning conflict, as did the controls, for shapes with sharp corners. Overall, IW was much faster than his controls to complete tracing shapes, consistent with an absence of visuo-proprioceptive conflict, whereas KS was slower than her controls, especially as the corners became sharper. She dramatically improved after a short period of practice while IW did not. We conclude that KS, who developed from birth without proprioception, may have some visually derived control of movement not under cognitive control, something not seen in IW. This allowed her to automate some writing and drawing actions, but impaired her initial attempts at mirror-tracing. In contrast, IW, who lost somatosensation as an adult, cannot automate these visually guided actions.

Perception of body shape and size without touch or proprioception: evidence from individuals with congenital and acquired neuropathy.

The degree to which mental representations of the body can be established and maintained without somatosensory input remains unclear. We contrast two "deafferented" adults, one who acquired large fibre sensory loss as an adult (IW) and another who was born without somatosensation (KS). We compared their responses to those of matched controls in three perceptual tasks: first accuracy of their mental image of their hands (assessed by testing recognition of correct hand length/width ratio in distorted photographs and by locating landmarks on the unseen hand); then accuracy of arm length judgements (assessed by judgement of reaching distance), and finally, we tested for an attentional bias towards peri-personal space (assessed by reaction times to visual target presentation). We hypothesised that IW would demonstrate responses consistent with him accessing conscious knowledge, whereas KS might show evidence of responses dependent on non-conscious mechanisms. In the first two experiments, both participants were able to give consistent responses about hand shape and arm length, but IW displayed a better awareness of hand shape than KS (and controls). KS demonstrated poorer spatial accuracy in reporting hand landmarks than both IW and controls, and appears to have less awareness of her hands. Reach distance was overestimated by both IW and KS, as it was for controls; the precision of their judgements was slightly lower than that of the controls. In the attentional task, IW showed no reaction time differences across conditions in the visual detection task, unlike controls, suggesting that he has no peri-personal bias of attention. In contrast, KS did show target location-dependent modulation of reaction times, when her hands were visible. We suggest that both IW and KS can access a conscious body image, although its accuracy may reflect their different experience of hand action. Acquired sensory loss has deprived IW of any subconscious body awareness, but the congenital absence of somatosensation may have led to its partial replacement by a form of visual proprioception in KS.

Loss of haptic feedback impairs control of hand posture: a study in chronically deafferented individuals when grasping and lifting objects.

Previous work has highlighted the role of haptic feedback for manual dexterity, in particular for the control of precision grip forces between the index finger and thumb. It is unclear how fine motor skills involving more than just two digits might be affected, especially given that loss of sensation from the hand affects many neurological patients, and impacts on everyday actions. To assess the functional consequences of haptic deficits on multi-digit grasp of objects, we studied the ability of three rare individuals with permanent large-fibre sensory loss involving the entire upper limb. All three reported difficulties in everyday manual actions (ABILHAND questionnaire). Their performance in a reach-grasp-lift task was compared to that of healthy controls. Twenty objects of varying shape, mass, opacity and compliance were used. In the reach-to-grasp phase, we found slower movement, larger grip aperture and less dynamic modulation of grip aperture in deafferented participants compared to controls. Hand posture during the lift phase also differed; deafferented participants often adopted hand postures that may have facilitated visual guidance, and/or reduced control complexity. For example, they would extend fingers that were not in contact with the object, or fold these fingers into the palm of the hand. Variability in hand postures was increased in deafferented participants, particularly for smaller objects. Our findings provide new insights into how the complex control required for whole hand actions is compromised by loss of haptic feedback, whose contribution is, thus, highlighted.

Proprioceptive loss and the perception, control and learning of arm movements in humans: evidence from sensory neuronopathy.

It is uncertain how vision and proprioception contribute to adaptation of voluntary arm movements. In normal participants, adaptation to imposed forces is possible with or without vision, suggesting that proprioception is sufficient; in participants with proprioceptive loss (PL), adaptation is possible with visual feedback, suggesting that proprioception is unnecessary. In experiment 1 adaptation to, and retention of, perturbing forces were evaluated in three chronically deafferented participants. They made rapid reaching movements to move a cursor toward a visual target, and a planar robot arm applied orthogonal velocity-dependent forces. Trial-by-trial error correction was observed in all participants. Such adaptation has been characterized with a dual-rate model: a fast process that learns quickly, but retains poorly and a slow process that learns slowly and retains well. Experiment 2 showed that the PL participants had large individual differences in learning and retention rates compared to normal controls. Experiment 3 tested participants' perception of applied forces. With visual feedback, the PL participants could report the perturbation's direction as well as controls; without visual feedback, thresholds were elevated. Experiment 4 showed, in healthy participants, that force direction could be estimated from head motion, at levels close to the no-vision threshold for the PL participants. Our results show that proprioceptive loss influences perception, motor control and adaptation but that proprioception from the moving limb is not essential for adaptation to, or detection of, force fields. The differences in learning and retention seen between the three deafferented participants suggest that they achieve these tasks in idiosyncratic ways after proprioceptive loss, possibly integrating visual and vestibular information with individual cognitive strategies.

Mania reduces perceived pain intensity in patients with chronic pain: preliminary evidence from retrospective archival data.

OBJECTIVE: Bipolar disorder is associated with poor pain outcomes, but the extant literature has not taken into account how mania or hypomania - a central feature of bipolar disorders - influences pain intensity. The objective of this study was to describe whether patients recalled experiencing reduced pain intensity during manic or hypomanic episodes. DESIGN AND SETTING: This study used a retrospective design using archival data from patient's medical records. SUBJECTS: A total of 201 patients with chronic pain with bipolar I (39.6%) or bipolar II (60.4%) disorder who were undergoing a psychological evaluation for an interventional pain procedure were included in this study. METHODS: Patients underwent a semistructured interview where they were asked if they recalled reductions in pain intensity during their most recent manic or hypomanic episode. The proportion of patients who responded "yes" versus "no" to this question was the primary outcome variable. RESULTS: Results reveal that 64.2% of patients recalled experiencing a reduction in pain intensity during their most recent manic or hypomanic episode. CONCLUSION: Perceptions of reduced pain intensity during mania or hypomania may contribute to a cycle of increased activity during manic episodes, which may increase pain over time. It may also lead to false-positive findings on spinal cord stimulator trials and diagnostic pain blocks, among other interventional pain procedures. The preliminary findings of this study highlight the clinical importance of assessing for bipolar disorders in patients with chronic pain.

Generalization of force-field adaptation in proprioceptively-deafferented subjects.

Humans have the remarkable ability to adapt their motor behaviour to changes in body properties and/or environmental conditions, based on sensory feedback such as vision and proprioception. The role of proprioception has been highlighted for the adaptation to new upper-limb dynamics, which is known to generalize to the opposite, non-adapted limb in healthy individuals. Such interlimb transfer seems to depend on sensory feedback, and the present study assessed whether the chronic loss of proprioception precludes interlimb transfer of dynamic adaptation by testing two well-characterized proprioceptively-deafferented subjects. These had to reach toward visual targets with vision of the limb. For both deafferented subjects, we observed adaptation of the dominant arm to Coriolis forces and after-effects on non-dominant arm movements in different movement directions, thus indicating interlimb transfer. Overall, our findings show that motor learning can generalize across limbs and movement directions despite the loss of proprioceptive afferents.

The fusimotor and reafferent origin of the sense of force and weight.

Signals associated with the command the brain sends to muscles are thought to create the sensation of heaviness when we lift an object. Thus, as a muscle is weakened by fatigue or partial paralysis (neuromuscular blockade), the increase in the motor command needed to lift a weight is thought to explain the increasing subjective heaviness of the lifted object.With different fatiguing contractions we approximately halved the force output of the thumb flexor muscles, which were then used to lift an object. For two deafferented subjects the perceived heaviness of the lifted object approximately doubled, in keeping with the central-signal theory. However, for normal subjects this resulted in objects feeling the same or lighter, inconsistent with the central-signal theory but consistent with the expected effects of the conditioning contractions on the sensitivity of peripheral receptors. In separate experiments we subjected the forearm muscles to complete paralysis with a non-depolarising neuromuscular blocking agent and then allowed them to recover to approximately half-force output. This also resulted in objects feeling lighter when lifted by the semi-paralysed thumb, even though the motor command to the motoneurons must have been greater. This is readily explained by reduced lift-related reafference caused by the prolonged paralysis of muscle spindle intrafusal fibres.We conclude that peripheral signals, including a major contribution from muscle spindles, normally give rise to the sense of exerted force. In concept, however, reafference from peripheral receptors may also be considered a centrally generated signal that traverses efferent and then afferent pathways to feed perceptual centres rather than one confined entirely to the central nervous system. These results therefore challenge the distinction between central- and peripheral-based perception, and the concept that muscle spindles provide only information about limb position and movement.

Exercise slips in high-risk situations and activity patterns in long-term exercisers: an application of the relapse prevention model.

BACKGROUND: Key factors in successful long-term exercise maintenance are not well understood. The Relapse Prevention Model (RPM) may provide a framework for this process. PURPOSE: The purpose of this study was to examine the relationships among characteristics of exercise high-risk situations, components of the RPM relevant to exercise slips, and follow-up exercise outcomes in long-term community exercisers. METHODS: We obtained long-term exercisers' (N=65) open-ended responses to high-risk situations and ratings of obstacle self-efficacy, guilt, and perceived control. High-risk situation characteristics, cognitive and behavioral coping strategies, and exercise outcomes were examined. RESULTS: High-risk situation characteristics included bad weather, inconvenient time of day, being alone, negative emotions, and fatigue. Being alone was associated with lower incidence of exercise slip. Positive cognitive coping strategies were most commonly employed and were associated with positive exercise outcome for both women and men. Guilt and perceived control regarding the high-risk situation were associated with exercise outcomes at follow-up, but only among the men (n=28). CONCLUSIONS: Findings confirm and extend previous work in the application of the RPM in examining exercise slips and relapse. Measurement issues and integration approaches from the study of relapse in addiction research are discussed.

Dissociated secondary hyperalgesia in a subject with a large-fibre sensory neuropathy.

In the skin surrounding a site of injury, hyperalgesia develops to mechanical stimuli. Two types of secondary hyperalgesia (to light touch and punctate stimuli) have recently been differentiated, based on different durations and sizes of the area involved. We studied secondary hyperalgesia in a subject who had a loss of myelinated afferent nerve fibres below the neck that spared the A delta group. Stroking with a cotton swab was not perceived anywhere on affected skin either before or after injection of 60 micrograms of capsaicin. Thus, there was no hyperalgesia to light touch. Capsaicin injection into the volar forearm evoked normal pain and flare. A von Frey probe exerting a force of 40 mN was perceived as sharp. The sensation of sharpness was more pronounced up to 2 cm outside the flare zone for at least 16 min following the injection (tested with a 200 mN von Frey probe). Thus, hyperalgesia to punctate stimuli developed as in healthy subjects. These data support the model that hyperalgesia to light touch (allodynia) is due to sensitisation of central pain-signaling neurones to low-threshold mechanoreceptor input (A beta fibres). In contrast, punctate hyperalgesia is likely to be due to sensitisation to nociceptor input (A delta or C fibres).