Integrating self-localization, proprioception, pain, and performance.
Neuroplasticity is one of the most widely studied forms of a wider phenomenon, which we call "bioplasticity." (6) Studies of neuroplasticity have directly compared professional dancers with non-dancers. (3,4,7) The impetus behind such studies appears intuitive: professional dancers are usually extensively trained, typically from a very young age, to organize sequences of fine motor acts within a defined space, and, at the same time, to exert strict control over their body posture. Furthermore, they often need to synchronize their body movements with the movements of other dancers and with different rhythms and moods. In other words, the processing of multisensory information coming from and about the surrounding space would seem to be highly honed in professional dancers. (4)
In the present paper, we focus on the concept of self-localization and its integration with the monitoring of peripersonal space (i.e., the space that surrounds the body), within the context of modern concepts of pain. We will also provide recent findings in the field of pain education and management, and in our understanding of bodily representations in the context of optimizing performance and injury prevention for both dancers and dance teachers, we will draw on recent insights from behavioral, clinical, neuroimaging, and physiological research.
Representations of the Body
To grasp the concept of how we maintain a cortical representation of the location and position of our own body parts, it is first helpful to discuss the representation of the body itself. Representation of the body refers to the concept that the brain holds maps, or templates, of our body, in the form of networks of brain cells. These internally held or "brain-grounded" representations constitute reference points for adjustments and commands involving the body. A very large literature on proprioception taps into this idea (see Proske and Gandevia (8) for a review), but perhaps an even larger literature encompasses discussion of how our body "feels to us" (e.g., in terms of temperature, position, pain, or stiffness).
Of all the ways our body can "feel to us" perhaps the most compelling feeling is that of pain. Pain is by definition unpleasant and is felt somewhere, most often in the body (although phantom limb pain--pain in a limb that does not exist and may not ever have existed (9)--is a notable exception). Modern conceptualizations of pain emphasize its protective function, such that pain can be considered an unpleasant sensory and emotional experience that has a particular bodily location and that compels us to protect the painful body part. (10) For example, pain somehow sets the limits beyond which dancers cannot push themselves without serious damage to their body. As with other elite athletes, (11) dancers' high-level interoceptive ability (i.e., the ability to efficiently interpret body signals) changes how they might interpret the meaning of their pain: is it just that pain that comes when stretching my calf or am I about to sprain my ankle? Is this just pain from a particularly demanding training session or am I about to get severely injured because I am overstressing an already injured body part?
The localization of pain is a prerequisite to the pain itself, as it is for other bodily feelings. (12) Unlike other bodily feelings, however, whether or not pain occurs depends on a complex evaluative process targeting the biological advantage or otherwise of protective action. (13) Pain can, therefore, be considered a perceptual inference based on a best guess that danger to body tissue exists and protective action is required. (10) It is no surprise, then, that pain depends on cortical representations of both threat to the body and the body itself.
Any discussion of bodily representations can encounter problems of multiple and ambiguous definitions. The term "body representation" itself is a case in point; it means different things to different people, although two broad interpretations dominate. One interpretation articulates several discrete representations that each have somewhat different functions and operate somewhat independently. (14-20) These discrete representations fall into two categories, the "body schema," which can be thought of as comprising the sensorimotor representations that guide action, and the "body image," which comprises all of the other bodily representations--i.e., those that are not concerned with action. The terms "body schema" and "body image" have a long history (Fig. 1) (21) dogged by ambiguous and inconsistent definitions. (22) However, a growing body of literature, including the arrival of "body image disorder," which pertains to feelings about one's body (itself a topic of some interest among dancers), (23-25) suggests that the various representations are not as distinct and independent of one another as was previously thought (for a discussion of body image and body schema see de Vignemont (26)).
The second broad interpretation of "body representation" articulates a more holistic view, that of a unified and dynamic representation of the body. One specific theory, born from the inadequacy of conventional theories when it comes to explaining perplexing pain states, such as phantom limb pain, is that of the "neuromatrix." (27) According to the neuromatrix theory, there is an "anatomical substrate of the body-self," represented by a large and widespread network of neurons that create loops between the thalamus and the cortex and between the cortex and the limbic system. These loops are proposed to subserve both the control of movement and the emergence of pain (Fig. 2).
We consider that the neuromatrix theory constituted a great step forward in terms of our understanding of a variety of painful conditions. It probably also laid the groundwork for the development of literature on disruption of cortical mechanisms in those with chronic pain. (28,29) However, the neuromatrix theory has also been criticized for being too conceptual. Although an anatomical substrate is core to the theory, no specific neuroanatomy has been proposed, except, perhaps, the representation of the surfaces of the body held in the primary somatosensory cortex, a sensory receptive area critical to the sense of touch. (30)
The Cortical Body Matrix
A further evolution of the neuromatrix theory, the cortical body matrix theory, posits "a multisensory representation of peripersonal space and of the space directly around the body" (31) (Fig. 3) and draws on a wide scope of neuroimaging, neurophysiological, and behavioral data to offer possible neural substrates (see below). Nonetheless, the cortical body matrix remained a "conceptual" theory, with which to make sense of a very large body of knowledge, rather than a physical entity that could be imaged or extracted.
One of the major shifts in thought captured by the cortical body matrix theory is the integral role of spatial processing. Localization depends on spatial processing and is based on several brain-based coordinate systems, which we can call "frames of reference." (12) Some examples are an anatomical frame of reference (based on the anatomical position of each body part--the right hand is attached to the right wrist, which is in turn attached to the right forearm, and so forth), a limb-based frame of reference (i.e., a stimulus to the hand occurs near the end of the forearm), and a body midline-based frame of reference (i.e., the right arm most of the time occupies the right side of space, but it can also occupy the left side of space when crossed over the body midline).
The cortical body matrix theory allocates a potentially pivotal role to the body-centered frame of reference, such that all of the sensory events that occur on the right side of space are mapped as "right," even if they involve a body part that belongs to the left side of the body (i.e., mapped "left" according to an anatomical frame of reference). This idea of a body-centered representation provides a putative explanation for many of the spatially defined disturbances that are seen in clinical painful disorders. One example is complex regional pain syndrome (CRPS), an exquisitely painful disorder associated with multiple system dysfunction such as disturbances of blood flow, sweating, hair and nail growth, and motor dysfunction (see Marinus et al. (32) for a review of clinical features and pathophysiology). There is a growing body of evidence that dysfunctions associated with this body-centered frame of reference contribute significantly to some of the problems of CRPS, including pain, while also having relevance for other painful conditions and injuries, such as, for example, unilateral back pain (33,34) and osteoarthritic knee pain. (35,36)
The spatially defined disruptions observed in association with pain can be profound; for example, people with CRPS of one hand have a cool side of space. That is, the affected hand, which is normally somewhat cooler than the healthy hand, warms up and resting pain is slightly relieved when the hand is shifted to the "unaffected" side. So too, the healthy hand cools down when it is shifted to the affected side. (37-39) Tactile processing (40) and motor control (41) are also disrupted in a spatially defined way. (42) The relevance of these types of disturbance extends well beyond pathological pain disorders, such as CRPS or unilateral back pain, because they raise the possibility of spatial mapping as a cause of other disruptions. Moreover, spatial features of chronic pain might be a potentially important target for treatment during rehabilitation. (43) For example, while at rest during recovery from an injury, just imagining the performance of precise movements with the affected body part should offer benefit for dancers. Thus, the cortical representation of that body part, together with its range of movement, is kept active, even though the body part itself is in fact at rest. These findings suggest that prolonged inaccurate or potentially harmful input associated with a certain part of space (e.g., the space normally occupied by the right hand) starts to affect the representation of that part of space. It is as though pain, for example, has adopted or invaded a region of space (i.e., the right side), rather than being confined to the representation of a certain body part (i.e., the right hand per se).31 That disrupting spatial mapping capacity decreases pain intensity in healthy volunteers, (12,44,45) lending weight to these ideas.
The cortical body matrix supposes a tight and functional connection between cognitive representations of the body and homeostatic representations of the body, a supposition with potentially profound implications for the performing arts because profound transformations of cognitive representations (i.e., of "self") are fundamental to the arts. For instance, this is the case of dancers wearing pointe shoes; the representation of their feet needs to be quickly updated in order to be able to perform. This includes small changes in posture, muscle contraction, the way the feet make contact with the floor, and so on. When the dancer takes off the pointe shoes, the feet representations will again be updated. These tight functional connections have been demonstrated in several ways. For example, inducing the illusion that one's hand has been "replaced" by an artificial counterpart, via the rubber hand illusion (46) (see below) reduces the temperature (47) and histamine reactivity (48) of the "replaced" hand. Amputees with a vivid phantom limb could learn to perform physiologically impossible movements with their phantom limb. However, they were successful only when a change in the cortical representation of their phantom limb occurred. That is, the acquisition of the previously impossible skill coincided with the generation of a novel structure of the phantom.
What is more, when the new bodily structure representation is formed, previously possible movements became less possible. (49) Just think how remarkable this really is: the felt structure of the phantom limb and the possible movements of the phantom limb really do go hand in hand and change if one instantaneously changes the other. This has potentially profound implications for dance performance, because it suggests the possibility that imagery with regard to skill acquisition may well be even greater than has been previously thought. Such changes in the felt body have a dark side too: people with CRPS feel that their painful limb is bigger than it really is, (50,51) and magnifying the visual input further 1. induces a feeling that the limb is even bigger, and 2. increases the swelling evoked by movement, even though the movements themselves are identical. (52) We tentatively propose that these findings raise the speculative but not outrageous possibility that cognitively induced perceptions of our body, such as those induced in method acting or dancing, have physiological effects on our body; a matter we revisit below.
Another fundamental tenet of the cortical body matrix, that is particularly relevant to dance, is the integration of our representation of space with our representation of the body, a "coarse representation of the body and the space around it," common to different individuals (31) (remembering, of course, that not just humans, but all mammals share the basic neuroanatomical structures (53)). This idea might find support in virtual reality research in which participants have been shown to adapt very quickly to sometimes substantial changes to their body shape, (54) even implausible ones. (55,56) Moreover, illusions that allow a participant to "adopt" a racially distinct body, or a child's body, or the body of an elderly person, can also induce a shift in attitudes toward people from those distinct groups. (54,57) Obviously, this too has potentially profound implications for artistic performance; might adopting the physical aspects of a character early in rehearsal facilitate adoption of their psychological aspects? Such propositions may seem intuitive to many artists but until recently have had very little empirical support.
There are implications here too for pain and other protective outputs, most notably movement. For example, if any credible evidence of danger to body tissue has the potential to increase protective outputs (i.e., increase pain and protective motor output), (6,10,13) then any credible evidence of danger to body tissue also has the potential to disrupt, or indeed "compete against," (43) non-protective outputs (other bodily feelings and movements) required for artistic performance. Since credible evidence of danger encompasses nociceptive and non-nociceptive domains, it is not only nociceptive input that can disrupt performance but also other sensory cues that impart danger according to the meaning attributed to them. (58-60) Moreover, danger cues, such as beliefs associated with the condition of the tissues or the threat posed to them (for example the belief that dancing is associated with stress fractures), have the capacity not only to increase the regulation of pain and other protective outputs, but to modulate physiological regulation of the body part involved. This remarkable complexity brings a new level of impact to threat-related cognitions or expectations and their potential to influence biological processes in the tissues of the body.
Self-Localization and Peripersonal Space
The recent expansion in our understanding of the relationship between pain, our sense of self, and our performance has triggered many researchers to revisit some core concepts. The "self" (i.e., what describes us as individuals) is defined and continuously updated by everyday experiences and explorations of the surrounding world, and it includes a wide range of aspects, such as physical sensations, emotions, and feelings. Two questions are integral to the representation of the self: 1. how do we know that a certain body (and its parts) belong to us (i.e., the "sense of ownership"), and 2. how do we know the location of our own body and its parts in space (i.e., "self-localization")? These two aspects are closely related. Indeed, the perceived state of our own body seems to modulate our perception of peripersonal space, (61,62) but here we will focus on self-localization. In order to produce fine motor acts, such as those involved in dance, self-localization is crucial, because each body part needs to occupy a specific position relative to other body parts, to the rest of the body as a whole, to the environment, and often to the bodies of other dancers. However, self-localization depends on mechanisms that appear to be differentially modulated in the presence of threat.
Proprioception is at the very core of self-localization. Proprioception includes "the senses of limb position and movement, the sense of tension or force, the sense of effort, and the sense of balance." (8) In a normal, threat-free situation, we are usually unaware of our proprioceptive computations, probably because they are so effective; we are seldom surprised by the location of a body part, and our proprioceptive errors are so rapidly and automatically corrected that they do not reach awareness. For example, the majority of people would not be aware of the difference in grasp strength applied to hold a cup of coffee or a delicate egg, simply because they are perfectly able to perform both actions. However, consider if the cup was made of paper and contained dangerously hot water. We would then allocate more resources to monitoring grasp, location, and body position so as to minimize risk. These resources might be taken from other tasks. Alternatively, consider the situation, common in pain, where one perceives that movement error will put body tissue at risk. The increased surveillance so induced requires resources that might be taken from other tasks; when optimal task performance is required, such situations can bring their own substantial cost. The point here is that the less margin for error involved in a task, the less margin for error exists between perceived danger and true danger. This is critical for high performance activities including dance, where suboptimal performance may be the difference between success and failure.
Our remarkable, usually "automatic," proprioceptive capacity has been widely studied and is integrated within the cortical body matrix theory. During non-reflexive movements, the sensory input likely to be generated by the movement is anticipated. This predicted sensory input is compared to the sensory input generated during the actual movement (including, but not limited to, proprioceptive somatosensory input). If a discrepancy is detected, the motor output is rapidly adjusted; however, it is important to emphasize that there are rapid ballistic movements, such as the final part of the motor sequence needed to throw a ball, that are hardly updated. This process is ongoing and "online." With respect to localization per se, when the predicted and perceived sensory inputs do not match, self-localization is momentarily disrupted and less accurate (i.e., the agent does not know precisely where their limb is), a situation that will usually trigger extra surveillance, perhaps via vision or top-down modulation of proprioceptive input. (8)
The Neural Correlates of Body Representation
The precise neural mechanisms that might subserve a cortical body matrix (31) remain to be elucidated. Nonetheless, there are already sufficient data to drive research forward with clear hypotheses. As shown in Figure 3, a widespread cortical network is probably involved. The primary sensory cortex (S1) is acknowledged to subserve the somatotopic representation of the body, (63) although, critically, it does not hold "the sense of touch"; S1 activation in response to tactile stimuli is consistent whether or not the touch is perceived. (64) Areas such as the premotor cortex, the superior parietal cortex, (65) the operculum, and the insula (66) are involved in the sense of ownership of one's own body. The posterior parietal cortex is important in the processing and integration of spatially based information coming from the body (67) but also from the other senses. That is, the posterior parietal cortex seems to be very important in multisensory integration underpinning the construction of the representations of the space that surrounds us and our location within it. (31) Consistent with the unified body representation approach, the posterior parietal cortex has strong connections with the insular cortex, which, among several other functions and together with the brainstem, plays an important role in interoceptive awareness, homeostasis, and autonomic regulation. (68,69) Indeed, experimentally disrupting the posterior parietal cortex using transcranial magnetic stimulation immediately disrupts thermoregulatory control. (70)
The temporoparietal junction (TPJ) seems to be particularly important for self-localization, and damage to the TPJ has been documented in those patients undergoing out of body experience. (71) Intriguingly, the TPJ is active during different cognitive and social tasks that involve a shift in perspective from one's own point of view to another's, (72) thus taking the phrase "seeing someone else's point of view" beyond the merely metaphorical (on this issue see also Serino et al. (73)).
There is no doubt that the ability to localize one's own body parts in space is complex; it involves many brain areas and much distributed information processing. One advantage of taking a system approach to investigating localization is the ability to utilize the massive redundancy of the human brain. That is, the exact neurons that mediate our pain, our sense of ownership, localization, thermoregulation, motor output, and so on are not identical between individuals and, indeed, are not fixed within an individual. The brain is, in fact, a dynamic representational organ; we have known for over a century that, for example, stimulating specific primary motor cortex cells will evoke one movement one day and a different movement the next. (74,75) Reduction in the usual variability of motor output itself is considered a marker of reduced redundancy within motor networks, is associated with ongoing pain, and closely reflects cognitive appraisals of threat to body tissue. (76-78)
Body Illusions: How to (Temporarily) Disrupt Self-Localization
Any neural representation of the body clearly needs to be extremely flexible. During most activities, not least of all dance, body posture and, in turn, the relationship between one's own body parts and the surrounding environment is constantly changing (interestingly, music is another crucial element that dancers must take into account while performing, but thorough discussion of the multisensory aspects of dance lies beyond the scope of this paper). Vision is a particularly rapid and reliable sensory input and therefore often dominates self-localization. However, dancers cannot rely only on vision, which introduces important questions about the relative influence over the cortical body matrix of different sensory inputs. (79-81) One well-used method of asking these questions (e.g., what is vision's role in self-localization?) is by means of the so-called rubber hand illusion (RHI), (46) possibly one of the most widely known and used bodily illusions over the last decade or so. Briefly, in this illusion one of the participants' arms is placed out of sight while a fake arm lies in view and aligned with the real arm. The real and fake hands are then stroked simultaneously, and after a few seconds, the participant starts to perceive the tactile stimuli as originating from the fake hand. The suggestion here is that the rubber hand becomes integrated into the participant's body representation, in order to maintain its own integrity and in addition to preserve that fundamental sense of ownership toward one's own body. The effects induced by the rubber hand illusion (and their relevance for the study of body representation) have been widely studied. As far as self-localization is concerned, when participants are asked to localize their hidden hand, they typically point to a spot between the real hand and the fake hand. This effect is called "proprioceptive drift." (82)
Proprioceptive drift has been widely held to represent a valid and bias-free method for assessing the strength of the RHI, because the amount of drift positively correlates with the vividness of the sense of feeling the touch on the rubber hand. (46,83,84) However, according to various investigators, simply having one's hands hidden from view can induce proprioceptive drift, (85,86) even in the absence of a prosthetic hand. (87) The link between ownership and self-localization, once thought to be very close, has also been questioned in recent years by numerous studies that dissociate the two measures. (72,87) What causes the shift in localizing one's own body parts if not (or, possibly, not solely) the sense of ownership? Changes in self-localization without changes in body ownership have been produced experimentally (72) and have been documented in neurological patients. (88) This, then, raises an intriguing question: Is it possible to lose knowledge of where a body part is without losing one's sense of ownership over it? A relatively new illusion, the disappearing hand trick (DHT), (89) sheds some light on this issue. In the DHT, participants see real-time video footage of their hands. However, the footage can be manipulated such that the seen position of their hands is not congruent with their true position; when this visual manipulation takes place, the hands are perceived to be close together when, in fact, they are far apart. It is a compelling illusion; when the participants' right hand disappears from view and they try to reach it with their (visible) left hand, they cannot find it; i.e., they underestimate the position of their hidden hand by touching the spot where they last saw it. They can sense that their right hand is still there, but they really do not know where it is. Post-hoc unsolicited comments clearly show that during the illusion participants are mystified as to quite where their hand has gone. Nevertheless, they do not report no longer owning it.
We have recently utilized the DHT in order to investigate the predominance of vision over proprioception in self-localization and the process of shifting from a vision-dominated perception to a proprioception-dominated one. (90) Over time the predominance of visually-encoded location fades away, as does the visual trace of the hand, leaving the participants to rely on proprioceptively-encoded localization. An automatic updating of the position of the right hand seems to occur even if no movement is required at all; a discovery that is consistent with the idea that the less variable input to the cortical body matrix exerts the stronger influence and is consistent with an evolutionary advantage of being best placed to move in case of unexpected danger.
This principle is well explained by the maximum likelihood estimation theory (MLE) (91): When people perceive a stimulus and produce a judgment based on that perception, the judgment tends to be influenced most by the least "variable" or more "trusted" sense. Where vision is available, it is usually the most trusted sense (but see van Beers (81) for optimal statistical integration of vision and proprioception in self-localization when both vision and proprioception are available). However, dancers may have a particular expertise in relying on proprioceptive input (and perhaps vestibular input) more than vision. There are other examples of such expertise: musicians do not need to watch their fingers to know their location while playing their instruments; potters and fencers rely more on tactile information than does the general population when vision is distorted (92); dancers must "trust" their proprioception in performing a movement, because most of the time visual feedback is not available or simply not useful for the purpose of the motor act. (93) One might predict that the differential influence that we normally see between vision and proprioception--vision exerting much greater weight than proprioception and proprioception slowly influencing localization once vision is rendered useless--would be lower in dancers than it is in the wider population. However, just as importantly, one might predict that, in the presence of ongoing pain, this enhanced influence of proprioceptive input will be lost. Remembering that pain depends on perceived need to protect bodily tissue, not on injury or nociception per se; we return to the simple principle that any credible evidence of danger to body tissue will increase the likelihood of pain and its intensity should it occur. Speculating again, one would then predict that ongoing pain would be associated with decreased proprioceptive acuity; a finding well established in non-dance populations. (35,94) Such questions are, as we have mentioned, of particular import in activities where the margin for performance error is minimal. Illusions, such as the DHT, which can probably be adapted for the lower limb, (35,36) provide an opportunity to investigate proprioceptive influence over self-localization in states of pain or apparent threat.
Proprioceptive performance can also be investigated by perturbing the proprioceptive organs themselves. Vibrating a tendon triggers muscle spindle receptors such that the central nervous system "detects" muscle lengthening when in fact there is none. (95,96) For example, a vibration delivered on the biceps brachii induces an illusion of elbow extension. A number of different illusions might be induced using this method, (97) which together attest to the importance of muscle spindles as principal proprioceptive receptors. (8) This kind of illusion of movement (and consequently of displacement) is quite strong and can involve the whole body.
What predictions might be tested? We would predict that dancers might have particularly strong vibration-induced illusions because of the extra influence proprioceptive input may have over localization. One might also predict that the RHI, which exploits visual-tactile synchrony at the cost of proprioceptive input, would be less vivid in dancers than in the wider population. In both cases, one might predict that dancers with chronic pain or indeed the conviction that a particular body part is vulnerable to injury might not show such evidence of heightened proprioceptive influence.
That dancers rehearse using mirrors, presumably prioritizing vision during a multimodal task, might in fact counter the subsequent requirement for proprioceptive input to dominate. Alternatively, spending a significant amount of time looking at body parts (in the mirror) that are usually out of view for the majority of non-dancers might lead to an increased tactile acuity in those body parts as compared to the general population. (98) Positive effects of tactile training on the affected part have been proven in people in pain. That mirror use can lead to an increased tactile acuity might be an advantage for dancers, especially with regard to rehabilitation. Such possibilities remain to be tested, but doing so would lay a potential foundation for assessment, both from a screening perspective--perhaps some individuals are "strongly proprioceptive" and therefore particularly suited to dancing--and from a rehabilitation perspective.
Dancers and Self-Localization
Proprioception and self-localization abilities acquire, for professional dancers, a whole new meaning. In this specific context, at each movement, the underlying aim goes far beyond mere practicalities, navigating efficiently the surrounding space or successfully grasping an object, but is also aesthetic. (93) Many studies have been conducted on professional dancers for their outstanding ability to self-localize their own body parts. For example, when a muscle is fatigued, the ability to replicate a particular joint angle or motion is normally impaired but not so in dancers. (99) The potential impact of this finding goes beyond dance because it strongly suggests that the impairments induced by fatigue are not dependent on changes in the properties of the end organ--the muscle and proprioceptive apparatus--but on the brain's capacity to compute accurate information in the presence of a compromised system. This is an exciting finding and has clear implications for training and injury prevention, not least the merit of training proprioceptive acuity during a state of fatigue.
Current perspectives of dancers' proprioceptive ability are not without contention, however. Jola and colleagues (100) suggest that the advantage might be limited to single joint movements or to one's best trained postures and does not transfer to other postures. Jola and colleagues' own work, however, clearly shows that dancers are better able than non-dancers to match the position of one hand with the contralateral hand under different conditions. They conclude that dancers have a more coherent body representation and, in their judgment, proprioception is more influential over perceived location, relative to vision, than it is in non-dancers. (100)
However, as mentioned above, from the perspective of facilitating optimal performance of the cortical body matrix, the habitual presence of mirrors during training but not during performance might seem counterproductive. Like non-dancers, dancers are more accurate at self-localization when visual information is "online," (101) yet, according to bioplasticity principles, training of this sort should both increase vision's influence and decrease proprioception's influence in future localization tasks. Perhaps moderation is the key here, because the precision offered by vision might be necessary as a biofeedback tool, and Jola's study (100) showed that even if dancers do practice with mirrors, they still do not rely on vision during localization tasks as much as non-dancers do. Particularly relevant is the requirement for dancers to perform in both the practical and aesthetical domain (93): "... vision is not a dancer's only guide: while dancers use mirrors as tools and often make self-corrections based on how a movement looks, looking at oneself in the mirror is often not the best guide to self-correction (to say nothing of the futility of looking at one's own body directly)," (Montero (93)). Montero's suggestion is, in fact, that proprioception from a dancer's perspective can be conceived of as an aesthetic sense. In other words, the judgment of correctness of a particular movement is based on how that specific movement is felt to be by the mover herself. In this sense, the choice of occupying a certain portion of space is not based on the practical aim of the movement, but rather there is an underlying aesthetic judgment that is entirely proprioceptive. The intimate connection between cognitive and behavioral outputs that is inherent to the cortical body matrix theory has potentially profound implications here: influences over how one's body feels--lithe, "in-character," injured, vulnerable, fat, stiff, strong, flexible, weak, beautiful--may well also have impact on localization and movement performance. The potential impact of this cannot be overestimated. Take the illusion of an adult "owning" a child's body and adopting more child-like attitudes, (54) or owning the body of a different raced person and becoming less racist. (57) As emphasized in the cortical body matrix theory, there seems little doubt that how we feel about physical self, our cognitive appraisals, our localization and proprioceptive abilities, our perceived need to protect, are all inextricably linked in complex ways.
A final consideration is the suggestion that proprioceptive "acuity" cannot be improved with training. (102) This would imply that the apparently large proprioceptive influence in dancers predates their dancing, but also clearly contradicts bioplasticity principles (i.e., if proprioception per se cannot be trained and thus modified, then plastic changes in the central nervous system related to this ability can hardly occur). Moreover, it has been suggested that professional dancers might, in fact, have poor proprioception acuity because of hypermobility (i.e., when the joints can be stretched farther than normal). (103) It is difficult to reconcile these suggestions with the wider body of literature and with the observation that performance on at least some localization tasks improves with training. (40,104-107) Indeed, there is a large body of literature on some localization tasks, for example, tactile acuity in those without peripheral receptor compromise but with pain, (108-110) and that literature clearly implies that performance is trainable. Perhaps the most parsimonious interpretation of the wider literature is that while there may be limited improvement available in peripheral mechanisms of somatosensation and proprioception, the influence of this input over localization and proprioceptive performance can indeed be enhanced.
The cortical body matrix theory (31) is clearly of immediate relevance to dance. The theory captures fundamental concepts in our understanding of how we localize body parts in space and navigate through that space and the potential influence of cognitive variables over behavioral outputs. Modern concepts of pain integrate smoothly with the cortical body matrix theory because they emphasize the fundamental importance of the perceived need for protection and the multiple systems that are used to protect us. Critically, the tight connection between the various outputs of the cortical body matrix, from homeostasis to bodily feelings (e.g., pain, stiffness, and fatigue), self-localization to bodily-related cognitions, strongly endorses a broad multisensory approach to dance training and performance. That dancers are faced with an atypical situation that requires both practical and aesthetic considerations further strengthens this connection and opens up new opportunities for experimental investigation of self-localization, bodily representation, and human performance. Finally, the wider body of literature suggests that any credible evidence of danger to body tissue may be sufficient to compromise performance. In the context of dance, where optimal performance reflects success or failure, considering the diverse array of danger cues might seem a critical part of injury and pain prevention.
Valeria Bellan, Ph.D., Sarah B. Wallwork, B.Physio.(Hons.), Alberto Gallace, Ph.D., Charles Spence, Ph.D., and G. Lorimer Moseley, D.Sc., Ph.D.
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Valeria Bellan, Ph.D., and Sarah B. Wallwork, B.Physio.(Hons.), Sansom Institute for Health Research, University of South Australia, and PainAdelaide, Adelaide Australia. Alberto Gallace, Ph.D., University of Milano-Bicocca, Bicocca, Italy. Charles Spence, Ph.D., University of Oxford, Oxford, United Kingdom. G. Lorimer Moseley, D.Sc., Ph.D., Sansom Institute for Health Research, University of South Australia, and PainAdelaide, Adelaide Australia and Neuroscience Research Australia, Sydney, Australia.
G. Lorimer Moseley, D.Sc., Ph.D., has received support from various pharmaceutical companies and athletic organizations and royalties and speaker fees for books and lectures on pain and rehabilitation.
Correspondence: G. Lorimer Moseley, D.Sc., Ph.D., GPO Box 2471 Adelaide South Australia 5001, Australia; firstname.lastname@example.org.
Caption: Figure 1 A very early example of discrete body representations. (Reproduced from Fludd R. Utriusque Cosmi, Maioris scilicet et Minoris, metaphysica, physica, atque technica Historia, Tomus II (The Metaphysical, Physical, and Technical History of the Two Worlds, Namely the Greater and the Lesser, Volume II). Frankfort, Germany: Oppenheim, 1619.)
Caption: Figure 2 The neuromatrix model. (Reproduced from Melzack R. Evolution of the neuromatrix theory of pain. The Prithvi Raj Lecture: presented at the third World Congress of World Institute of Pain, Barcelona 2004. Pain Pract. 2005 June:5(2):85-94. With permission.)
Caption: Figure 3 The cortical body matrix. 1, A widespread network of cortical brain areas are thought to be involved in body representation and, thus, in self-localization. However, a major role is also played by audition (2), and vision (3). In order to locate one's own body part, then both skin receptors (4), muscle spindles, and Golgi tendon organs (5) are crucial. Together, all these cues contribute to create a unique and coherent percept of one's own body, well described with the concept of cortical body matrix. In particular, the innovative aspect is the body-centered representation of the body itself (instead of a body part-centered representation), such as the right leg (7), which is usually in the right side of the space (8), can occupy the left side of the peripersonal space simply by one's crossing the leg over into the space where the left leg usually is. View this figure in color at https://doi.org/10.12678/1089-313X.21.124.
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|Author:||Bellan, Valeria; Wallwork, Sarah B.; Gallace, Alberto; Spence, Charles; Moseley, G. Lorimer|
|Publication:||Journal of Dance Medicine & Science|
|Date:||Jan 1, 2017|
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