Phantom limb experiences in congenital limb-deficient adults

Examining the prevalence of trans phantoms among transgender, nonbinary and gender diverse individuals: An exploratory study

Background

Trans phantoms are bodily sensations of gendered body parts that a person was not born with (i.e., a phantom penis experienced by a trans man, or a phantom vagina experienced by a trans woman). This is distinct from the experience of many transgender and gender diverse (TGD) people, who experience awareness of their bodies as missing a gendered body part, or configuration, which is a major characteristic of gender dysphoria.

Aims

Our purpose was to gain greater understanding of the prevalence and quality of trans phantoms.

Methods

Data was gathered through a brief, online survey on trans embodiment. Respondents who had both completed the survey, and were deemed appropriate for inclusion in the study, based on their survey responses, comprised our sample of 1,446 adults.

Results

Results indicated that trans phantoms are a typical embodied experience of TGD people. Almost 50% of study participants reported experiencing a trans phantom, most of whom also reported feeling erotic sensation in their phantom.

Conclusions

Though the phenomenon of trans phantoms is not universal, it is clearly one that warrants further study.

Pathophysiological and Neuroplastic Changes in Postamputation and Neuropathic Pain: Review of the Literature

Despite advancements in surgical and rehabilitation strategies, extremity amputations are frequently associated with disability, phantom limb sensations, and chronic pain. Investigation into potential treatment modalities has focused on the pathophysiological changes in both the peripheral and central nervous systems to better understand the underlying mechanism in the development of chronic pain in persons with amputations.

Methods

Presented in this article is a discussion outlining the physiological changes that occur in the peripheral and central nervous systems following amputation. In this review, the authors examine the molecular and neuroplastic changes occurring in the nervous system, as well as the state-of-the-art treatment to help reduce the development of postamputation pain.

Results

This review summarizes the current literature regarding neurological changes following amputation. Development of both central sensitization and neuronal remodeling in the spinal cord and cerebral cortex allows for the development of neuropathic and phantom limb pain postamputation. Recently developed treatments targeting these pathophysiological changes have enabled a reduction in the severity of pain; however, complete resolution remains elusive.

Conclusions

Changes in the peripheral and central nervous systems following amputation should not be viewed as separate pathologies, but rather two interdependent mechanisms that underlie the development of pathological pain. A better understanding of the physiological changes following amputation will allow for improvements in therapeutic treatments to minimize pathological pain caused by amputation.

Two senses of human limb position: methods of measurement and roles in proprioception

The sense of position of the body and its limbs is a proprioceptive sense. Proprioceptors are concerned with monitoring the body's own actions. Position sense is important because it is believed to contribute to our self-awareness. This review discusses recent developments in the debate about the sources of peripheral afferent signals contributing to position sense and describes different methods of measurement of position sense under conditions where vision does not participate. These include pointing to or verbal reporting of the perceived position of a hidden body part, alignment of one body part with the perceived position of another, or using memory-based repositioning tasks. The evidence suggests that there are at least two different mechanisms involved in the generation of position sense, mechanisms using different central processing pathways. The principal sensory receptor responsible for position sense is believed to be the muscle spindle. One criterion for identifying mechanism is whether position sense can be manipulated by controlled changes in spindle discharge rates. Position sense measured in two-limb matching is altered in a predictable way by such changes, while values for pointing and verbal reporting remain unresponsive. It is proposed that in two-limb matching the sensation generated is limb position in postural space. In pointing or verbal reporting, information is provided about limb position in extrapersonal space. Here vision is believed to play a role. The evidence suggests that we are aware, at the same time, of sensations of limb position in postural space as well as in extrapersonal space.

AAAPT Diagnostic Criteria for Acute Neuropathic Pain

OBJECTIVE

Acute neuropathic pain is a significant diagnostic challenge, and it is closely related to our understanding of both acute pain and neuropathic pain. Diagnostic criteria for acute neuropathic pain should reflect our mechanistic understanding and provide a framework for research on and treatment of these complex pain conditions.

METHODS

The Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership with the U.S. Food and Drug Administration (FDA), the American Pain Society (APS), and the American Academy of Pain Medicine (AAPM) collaborated to develop the ACTTION-APS-AAPM Pain Taxonomy (AAAPT) for acute pain. A working group of experts in research and clinical management of neuropathic pain was convened. Group members used literature review and expert opinion to develop diagnostic criteria for acute neuropathic pain, as well as three specific examples of acute neuropathic pain conditions, using the five dimensions of the AAAPT classification of acute pain.

RESULTS

AAAPT diagnostic criteria for acute neuropathic pain are presented. Application of these criteria to three specific conditions (pain related to herpes zoster, chemotherapy, and limb amputation) illustrates the spectrum of acute neuropathic pain and highlights unique features of each condition.

CONCLUSIONS

The proposed AAAPT diagnostic criteria for acute neuropathic pain can be applied to various acute neuropathic pain conditions. Both the general and condition-specific criteria may guide future research, assessment, and management of acute neuropathic pain.

Giving Up on Consciousness as the Ghost in the Machine

Consciousness as used here, refers to the private, subjective experience of being aware of our perceptions, thoughts, feelings, actions, memories (psychological contents) including the intimate experience of a unified self with the capacity to generate and control actions and psychological contents. This compelling, intuitive consciousness-centric account has, and continues to shape folk and scientific accounts of psychology and human behavior. Over the last 30 years, research from the cognitive neurosciences has challenged this intuitive social construct account when providing a neurocognitive architecture for a human psychology. Growing evidence suggests that the executive functions typically attributed to the experience of consciousness are carried out competently, backstage and outside subjective awareness by a myriad of fast, efficient non-conscious brain systems. While it remains unclear how and where the experience of consciousness is generated in the brain, we suggested that the traditional intuitive explanation that consciousness is causally efficacious is wrong-headed when providing a cognitive neuroscientific account of human psychology. Notwithstanding the compelling 1st-person experience (inside view) that convinces us that subjective awareness is the mental curator of our actions and thoughts, we argue that the best framework for building a scientific account is to be consistent with the biophysical causal dependency of prior neural processes. From a 3rd person perspective, (outside view), we propose that subjective awareness lacking causal influence, is (no more) than our experience of being aware, our awareness of our psychological content, knowing that we are aware, and the belief that that such experiences are evidence of an agentive capacity shared by others. While the human mind can be described as comprising both conscious and nonconscious aspects, both ultimately depend on neural process in the brain. In arguing for the counter-intuitive epiphenomenal perspective, we suggest that a scientific approach considers all mental aspects of mind including consciousness in terms of their underlying, preceding (causal) biological changes, in the realization that most brain processes are not accompanied by any discernible change in subjective awareness.

Motor Imagery Training of Reaching-to-Grasp Movement Supplemented by a Virtual Environment in an Individual With Congenital Bilateral Transverse Upper-Limb Deficiency

This study explored the effect of kinesthetic motor imagery training on reaching-to-grasp movement supplemented by a virtual environment in a patient with congenital bilateral transverse upper-limb deficiency. Based on a theoretical assumption, it is possible to conduct such training in this patient. The aim of this study was to evaluate whether cortical activity related to motor imagery of reaching and motor imagery of grasping of the right upper limb was changed by computer-aided imagery training (CAIT) in a patient who was born without upper limbs compared to a healthy control subject, as characterized by multi-channel electroencephalography (EEG) signals recorded before and 4, 8, and 12 weeks after CAIT. The main task during CAIT was to kinesthetically imagine the execution of reaching-to-grasp movements without any muscle activation, supplemented by computer visualization of movements provided by a special headset. Our experiment showed that CAIT can be conducted in the patient with higher vividness of imagery for reaching than grasping tasks. Our results confirm that CAIT can change brain activation patterns in areas related to motor planning and the execution of reaching and grasping movements, and that the effect was more pronounced in the patient than in the healthy control subject. The results show that CAIT has a different effect on the cortical activity related to the motor imagery of a reaching task than on the cortical activity related to the motor imagery of a grasping task. The change observed in the activation patterns could indicate CAIT-induced neuroplasticity, which could potentially be useful in rehabilitation or brain-computer interface purposes for such patients, especially before and after transplantation. This study was part of a registered experiment (ID: NCT04048083).

Where is my mouth? Rapid experience-dependent plasticity of perceived mouth position in humans

Several neural and behavioural studies propose that movements of the hand to the mouth are a key motor primitive of the primate sensorimotor system. These studies largely focus on sensorimotor coordination required to reach the mouth with the hand. However, hand-to-mouth movement depends on representing the location of the mouth. We report 5 experiments using a novel dental model illusion (DMI) that investigates the neural representation of mouth position. When participants used their right index finger to touch the teeth of an unseen dental model in synchrony with the experimenter's tactile stimulation of the participant's own teeth, participants felt that the position of their own teeth was shifted towards the dental model and stated that their right index finger was touching their actual teeth. This result replicated across four experiments and provides an oral analogue to the rubber hand illusion. Synchrony between the two tactile motions was necessary condition to elicit DMI (Experiment 3). DMI was moderately affected by manipulating the macrogeometric or microgeometric tactile properties of the dental model, suggesting cognitive images of one's own oral morphology play a modest role (Experiments 4 and 5). Neuropsychological theories often stress that hand-to-mouth movement emerges early in development or may even be innate. Our research suggests that general, bottom-up principles of multisensory plasticity suffice to provide spatial representation of the egocentric core, including mouth position.

The prevalence of phantom limb pain and associated risk factors in people with amputations: a systematic review protocol

BACKGROUND

The prevalence of phantom limb pain (PLP) in people with amputations is unclear because of the conflicting reports across the literature. It is proposed that the conflicting reports on the prevalence of PLP are a consequence of variations in the time period during which the studies were undertaken, countries in which the studies were conducted and recruitment processes implemented during collection of epidemiological data. In consideration of these factors, we aim to gather and critically appraise relevant literature to determine the prevalence estimate of and risk factors for PLP in people with amputations.

METHODS

We will use a customised search strategy containing relevant words and terms to search the following databases: MEDLINE/PubMed (via EBSCOhost), PsycINFO (via EBSCOhost), PsycArticles, Cumulative Index to Nursing and Allied Health Literature (CINAHL) (via EBSCOhost), Africa-Wide Information (via EBSCOhost), Health Source: Nursing/Academic Edition (via EBSCOhost) SCOPUS, Web of Science and Academic Search Premier (via EBSCOhost). The risk of bias assessment will be conducted using a risk of bias assessment tool for prevalence studies, and data will be extracted using a piloted customised data extraction sheet. Data extracted from individual studies will be entered into Review Manager 5 and assessed for clinical and statistical heterogeneity. Studies will be pooled for meta-analysis using the random-effects model to determine a summary estimate of the prevalence of PLP across included studies. A statistically significant level will be set at p < 0.05.

DISCUSSION

As far as we know, a systematic review and meta-analysis on the prevalence of, and risk factors for PLP in people with amputations has not been conducted. Given the varying reports in the literature, it is necessary to determine an estimate of the prevalence of PLP to generate an informed conclusion on this subject. The results of this review will be published in an internationally accredited journal and used to inform researchers, clinicians, policy-makers and the public about the burden of, and risk factors for PLP. This will be done with a further aim to improve the quality of pain management in society.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42018094821.

Chasing the Rainbow: The Non-conscious Nature of Being

Despite the compelling subjective experience of executive self-control, we argue that “consciousness” contains no top-down control processes and that “consciousness” involves no executive, causal, or controlling relationship with any of the familiar psychological processes conventionally attributed to it. In our view, psychological processing and psychological products are not under the control of consciousness. In particular, we argue that all “contents of consciousness” are generated by and within non-conscious brain systems in the form of a continuous self-referential personal narrative that is not directed or influenced in any way by the “experience of consciousness.” This continuously updated personal narrative arises from selective “internal broadcasting” of outputs from non-conscious executive systems that have access to all forms of cognitive processing, sensory information, and motor control. The personal narrative provides information for storage in autobiographical memory and is underpinned by constructs of self and agency, also created in non-conscious systems. The experience of consciousness is a passive accompaniment to the non-conscious processes of internal broadcasting and the creation of the personal narrative. In this sense, personal awareness is analogous to the rainbow which accompanies physical processes in the atmosphere but exerts no influence over them. Though it is an end-product created by non-conscious executive systems, the personal narrative serves the powerful evolutionary function of enabling individuals to communicate (externally broadcast) the contents of internal broadcasting. This in turn allows recipients to generate potentially adaptive strategies, such as predicting the behavior of others and underlies the development of social and cultural structures, that promote species survival. Consequently, it is the capacity to communicate to others the contents of the personal narrative that confers an evolutionary advantage—not the experience of consciousness (personal awareness) itself.

Adaptive and maladaptive neural compensatory consequences of sensory deprivation-From a phantom percept perspective

It is suggested that the brain undergoes plastic changes in order to adapt to changing environmental needs. Sensory deprivation results in decreased input to the brain leading to adaptive or maladaptive changes. Although several theories hypothesize the mechanism of these adaptive and maladaptive changes, the course of action taken by the brain heavily depends on the age of incidence of damage. The growing body of literature on the topic proposes that maladaptive changes in the brain are instrumental in creating phantom percepts, defined as the perception of a sensory experience in the absence of a physical stimulus. The current article reviews the mechanisms of adaptive and maladaptive plasticity in the brain in congenital, early, and late-onset sensory deprivation in conjunction with the phantom percepts in the different sensory domains. We propose that the mechanisms of adaptive and maladaptive plasticity fall under a universal construct of updating hierarchical Bayesian prediction errors. This theory of the Bayesian brain hypothesizes that the brain constantly compares its internal milieu with changing environmental cues and either adjusts its predictions or discards the change, depending on the novelty or salience of the external stimulus. We propose that adaptive plasticity reflects both successful bottom-up compensation and top-down updating of the model while maladaptive plasticity reflects failure in one or both mechanisms, resulting in a constant prediction-error. Finally, we hypothesize that phantom percepts are generated by the brain as a solution to this prediction error and are thus a manifestation of unsuccessful adaptation to sensory deprivation.

Etiology of phantom limb syndrome: Insights from a 3D default space consciousness model

In this article, we examine phantom limb syndrome to gain insights into how the brain functions as the mind and how consciousness arises. We further explore our previously proposed consciousness model in which consciousness and body schema arise when information from throughout the body is processed by corticothalamic feedback loops and integrated by the thalamus. The parietal lobe spatially maps visual and non-visual information and the thalamus integrates and recreates this processed sensory information within a three-dimensional space termed the "3D default space." We propose that phantom limb syndrome and phantom limb pain arise when the afferent signaling from the amputated limb is lost but the neural circuits remain intact. In addition, integration of conflicting sensory information within the default 3D space and the loss of inhibitory afferent feedback to efferent motor activity from the amputated limb may underlie phantom limb pain.

The role of the environment in eliciting phantom-like sensations in non-amputees

Following the amputation of a limb, many amputees report that they can still vividly perceive its presence despite conscious knowledge that it is not physically there. However, our ability to probe the mental representation of this experience is limited by the intractable and often distressing pain associated with amputation. Here, we present a method for eliciting phantom-like experiences in non-amputees using a variation of the rubber hand illusion in which a finger has been removed from the rubber hand. An interpretative phenomenological analysis revealed that the structure of this experience shares a wide range of sensory attributes with subjective reports of phantom limb experience. For example, when the space where the ring finger should have been on the rubber hand was stroked, 93% of participants (i.e., 28/30) reported the vivid presence of a finger that they could not see and a total of 57% (16/28) of participants who felt that the finger was present reported one or more additional sensory qualities such as tingling or numbness (25%; 7/28) and alteration in the perceived size of the finger (50%; 14/28). These experiences indicate the adaptability of body experience and share some characteristics of the way that phantom limbs are described. Participants attributed changes to the shape and size of their "missing" finger to the way in which the experimenter mimed stroking in the area occupied by the missing finger. This alteration of body perception is similar to the phenomenon of telescoping experienced by people with phantom limbs and suggests that our sense of embodiment not only depends on internal body representations but on perceptual information coming from peripersonal space.

The emergence of adolescent onset pain hypersensitivity following neonatal nerve injury

Background

Peripheral nerve injuries can trigger neuropathic pain in adults but cause little or no pain when they are sustained in infancy or early childhood. This is confirmed in rodent models where neonatal nerve injury causes no pain behaviour. However, delayed pain can arise in man some considerable time after nerve damage and to examine this following early life nerve injury we have carried out a longer term follow up of rat pain behaviour into adolescence and adulthood.

Results

Spared nerve injury (SNI) or sham surgery was performed on 10 day old (P10) rat pups and mechanical nociceptive reflex thresholds were analysed 3, 7, 14, 21, 28, 38 and 44 days post surgery. While mechanical thresholds on the ipsilateral side are not significantly different from controls for the first 2–3 weeks post P10 surgery, after that time period, beginning at 21 days post surgery (P31), the SNI group developed following early life nerve injury significant hypersensitivity compared to the other groups. Ipsilateral mechanical nociceptive threshold was 2-fold below that of the contralateral and sham thresholds at 21 days post surgery (SNI-ipsilateral 28 (±5) g control groups 69 (±9) g, p < 0.001, 3-way ANOVA, n = 6 per group). Importantly, no effect was observed on thermal thresholds. This hypersensivity was accompanied by macrophage, microglial and astrocyte activation in the DRG and dorsal horn, but no significant change in dorsal horn p38 or JNK expression. Preemptive minocycline (daily 40 mg/kg, s.c) did not prevent the effect. Ketamine (20 mg/kg, s.c), on the other hand, produced a dose-dependent reversal of mechanical nociceptive thresholds ipsilateral to the nerve injury such that thresholds return to control levels at the highest doses of 20 mg/Kg.

Conclusions

We report a novel consequence of early life nerve injury whereby mechanical hypersensitivity only emerges later in life. This delayed adolescent onset in mechanical pain thresholds is accompanied by neuroimmune activation and NMDA dependent central sensitization of spinal nociceptive circuits. This delayed onset in mechanical pain sensitivity may provide clues to understand the long term effects of early injury such as late onset phantom pain and the emergence of complex adolescent chronic pain syndromes.

Body integrity identity disorder: the persistent desire to acquire a physical disability

BACKGROUND

Body integrity identity disorder (BIID) is a rare and unusual psychiatric condition characterized by a persistent desire to acquire a physical disability (e.g., amputation, paraplegia) since childhood that to date has not been formally described in the psychiatric nosology. Most BIID sufferers experience a chronic and dysphoric sense of inappropriateness regarding their being able-bodied, and many have been driven to actualize their desired disability through surreptitious surgical or other more dangerous methods. This review aims to characterize the history and phenomenology of this condition, to present its differential diagnosis, and to consider possible etiologies, treatment options, and ethical considerations.

SAMPLING AND METHOD

Review of the psychiatric and neurological literature.

RESULTS

A growing body of data suggests the existence of a discrete entity with onset by early adolescence and a negative impact on functioning. Parallel neurological conditions and preliminary experimental investigations suggest a possible neurobiological component in at least a portion of cases. While attempts at treatment have been described, no systematic evidence for efficacy has emerged.

DISCUSSION

BIID is a unique nosological entity with significant consequences for its sufferers and as such may warrant inclusion in some form in the forthcoming DSM-5 and ICD-11.

The appearance of new phantom fingers post-amputation in a phocomelus

We report the unusual case of a woman with right upper limb phocomelia who, post-amputation of her right hand following trauma, sprouted a phantom hand that contained five digits, including a phantom thumb and index finger that had been absent since her birth. These two phantom digits were initially half normal size, however, more than three decades later, with mirror visual feedback treatment, she was able to elongate them to normal length. This suggests that a hardwired representation of a complete hand had always been present in her brain, but inhibited by the presence of afferents from the phocomelic hand. Amputation of the phocomelic hand then led to disinhibition of this dormant representation, and the emergence of a phantom hand with five fingers, which was then further enhanced by false visual feedback from a mirror. The case powerfully demonstrates the interaction of nature and nurture in creating and sustaining body image.

Motor cortex representation of the upper-limb in individuals born without a hand

The body schema is an action-related representation of the body that arises from activity in a network of multiple brain areas. While it was initially thought that the body schema developed with experience, the existence of phantom limbs in individuals born without a limb (amelics) led to the suggestion that it was innate. The problem with this idea, however, is that the vast majority of amelics do not report the presence of a phantom limb. Transcranial magnetic stimulation (TMS) applied over the primary motor cortex (M1) of traumatic amputees can evoke movement sensations in the phantom, suggesting that traumatic amputation does not delete movement representations of the missing hand. Given this, we asked whether the absence of a phantom limb in the majority of amelics means that the motor cortex does not contain a cortical representation of the missing limb, or whether it is present but has been deactivated by the lack of sensorimotor experience. In four upper-limb amelic subjects we directly stimulated the arm/hand region of M1 to see 1) whether we could evoke phantom sensations, and 2) whether muscle representations in the two cortices were organised asymmetrically. TMS applied over the motor cortex contralateral to the missing limb evoked contractions in stump muscles but did not evoke phantom movement sensations. The location and extent of muscle maps varied between hemispheres but did not reveal any systematic asymmetries. In contrast, forearm muscle thresholds were always higher for the missing limb side. We suggest that phantom movement sensations reported by some upper limb amelics are mostly driven by vision and not by the persistence of motor commands to the missing limb within the sensorimotor cortex. We propose that prewired movement representations of a limb need the experience of movement to be expressed within the primary motor cortex.

Effects of Practice, Visual Loss, Limb Amputation, and Disuse on Motor Imagery Vividness

Background. The ability to generate vivid images of movements is variable across individuals and likely influenced by sensorimotor inputs. Objectives. The authors examined (1) the vividness of motor imagery in dancers and in persons with late blindness, with amputation or an immobilization of one lower limb; (2) the effects of prosthesis use on motor imagery; and (3) the temporal characteristics of motor imagery. Methods. Eleven dancers, 10 persons with late blindness, 14 with amputation, 6 with immobilization, and 2 groups of age-matched healthy individuals (27 in control group A; 35 in control group B) participated. The Kinesthetic and Visual Imagery Questionnaire served to assess motor imagery vividness. Temporal characteristics were assessed with mental chronometry. Results. The late blindness group and dance group displayed higher imagery scores than respective control groups. In the amputation and immobilization groups, imagery scores were lower on the affected side than the intact side and specifically for imagined foot movements. Imagery scores of the affected limb positively correlated with the time since walking with prosthesis. Movement times during imagination and execution (amputation and immobilization) were longer on the affected side than the intact side, but the temporal congruence between real and imagined movement times was similar to that in the control group. Conclusions. The mental representation of actions is highly modulated by imagery practice and motor activities. The ability to generate vivid images of movements can be specifically weakened by limb loss or disuse, but lack of movement does not affect the temporal characteristics of motor imagery.

Central mechanisms in phantom limb perception: The past, present and future

Phantom limbs provide valuable insight into the mechanisms underlying bodily awareness and ownership. This paper reviews the complexity of phantom limb phenomena (proprioception, form, position, posture and telescoping), and the various contributions of internal constructs of the body, or body schema, and neuromatrix theory in explaining these phenomena. Specific systems and processes that have received little attention in phantom limb research are also reviewed and highlighted as important future directions, These include prosthesis embodiment and extended physiological proprioception (i.e., the extension of the body's "area of influence" that thereby extends one's innate sense of proprioception, mirror neurons and cross-referencing of the phantom limb with the intact limb (and the related phenomena of perceiving referred sensations and mirrored movements in the phantom form the intact limb). The likely involvements of the body schema and the body-self neuromatrix, mirror neurons, and cross-callosal and ipsilateral mechanisms in phantom limb phenomena all suggest that the perception of a "normal" phantom limb (that is, a non-painful phantom that has the sensory qualities of an intact limb) is more than likely an epiphenomenon of normal functioning, action understanding and empathy, and potentially may even be evolutionarily adaptive and perhaps necessary. Phantom pain, however, may be a maladaptive failure of the neuromatrix to maintain global bodily constructs.

Occurrence of phantom genitalia after gender reassignment surgery

Transsexuals are individuals who identify as a member of the gender opposite to that which they are born. Many transsexuals report that they have always had a feeling of a mismatch between their inner gender-based "body image" and that of their body's actual physical form. Often transsexuals undergo gender reassignment surgery to convert their bodies to the sex they feel they should have been born. The vivid sensation of still having a limb although it has been amputated, a phantom limb, was first described by Weir Mitchell over a century ago. The same phenomenon is also occurs after amputation of the penis or a breast. Around 60% of men who have had to have their penis amputated for cancer will experience a phantom penis. It has recently been shown that a significant factor in these phantom sensations is "cross-activation" between the de-afferented cortex and surrounding areas. Despite this it also known that much of our body image is innately "hard-wired" into our brains; congenitally limbless patients can still experience phantom sensations. We hypothesise that, perhaps due to a dissociation during embryological development, the brains of transsexuals are "hard-wired" in manner, which is opposite to that of their biological sex. We go on to predict that male-to-female transsexuals will be much less likely to experience a phantom penis than a "normal" man who has had his penis amputated for another reason. The same will be true of female-to-male transsexuals who have had breast removal surgery. We also predict that some female-to-male transsexuals will have a phantom penis even although there is not one physically there. We believe that this is an easily testable hypothesis, which, if correct, would offer insights into both the basis of transsexuality and provide farther evidence that we have a gender specific body image, with a strong innate component that is "hard-wired" into our brains. This would furnish us with a better understanding the mechanism by which nature and nurture interact to link the brain-based internal body image with external sexual morphology. We would emphasise here that transsexuality should not be regarded as "abnormal" but instead as part of the spectrum of human behaviour.

Phantom limb pain: a case of maladaptive CNS plasticity?

Phantom pain refers to pain in a body part that has been amputated or deafferented. It has often been viewed as a type of mental disorder or has been assumed to stem from pathological alterations in the region of the amputation stump. In the past decade, evidence has accumulated that phantom pain might be a phenomenon of the CNS that is related to plastic changes at several levels of the neuraxis and especially the cortex. Here, we discuss the evidence for putative pathophysiological mechanisms with an emphasis on central, and in particular cortical, changes. We cite both animal and human studies and derive suggestions for innovative interventions aimed at alleviating phantom pain.

A critical review of congenital phantom limb cases and a developmental theory for the basis of body image

Reports of phantom limbs amongst aplasics (i.e., subjects who congenitally lack one or several limbs) have often been presented as evidence that body image is 'hard-wired' in the brain and that neither sensory input nor proprioceptive feedback are essential to its formation. Although attempts have been made to account for these phantoms by other means, these have been on a case by case basis and no satisfactory alternative framework has been proposed. This paper collates the accounts of aplasic phantoms and presents them as compatible with a four-part hypothesis, in which body image is learnt from experience during both pre- and post-natal development, and in which cross-cortical connections and mirror neurons play prominent roles. This model unites several previously disparate theories to offer a viable solution to several longstanding phantom limb mysteries and serves to highlight avenues worthy of further inquiry.

Phantom limbs: The body in mind

INTRODUCTION

Advances in our knowledge of corporeal awareness is not limited to patients with amputations, however, until recently, the study of ''phantom limbs'' was neglected by comparison with less common disorders of body perception.

METHOD

Reasons for the neglect of this potentially informative and common condition are conspicuous by their absence in previous reviews. Over the past decade, however, experimental investigations of phantom limbs have revealed the dynamic neural processes that provide for both phantom and normal corporeal embodiment. Moreover, these findings helped to overturn widely held scientific assumptions regarding the extent of neural plasticity in the adult brain.

RESULTS

It is suggested that throughout medical history, the construct of ''phantom limbs'' posed a challenge to fundamental folk assumptions regarding the assumed relationship between body and mind.

CONCLUSION

Reluctance to entertain the counter-intuitive phenomenon of a ''limbless perception'' contributed to the comparative neglect of this fascinating phenomenon until the late 20th century.

Virtual movements activate primary sensorimotor areas in amputees: report of three cases

OBJECTIVE

In our multidisciplinary pain clinic, three patients with amputated limbs and with surgical indications for chronic motor cortex stimulation for phantom limb pain were selected for their ability to voluntarily move the missing limb. The sensation of being able to move a missing limb at will occurs quite frequently among traumatic amputees, but the ability to control it sufficiently to perform a functional magnetic resonance imaging (fMRI) examination is more rarely encountered. We used motor fMRI to study these virtual movements.

METHODS

In two patients with upper-limb amputations, movements of the stump, the normal hand, and the missing arm were studied. In a third patient with both legs amputated, movements of the stumps and of the missing feet were studied. The fMRI data were analyzed with the Statistical Parametric Map 96 software and reformatted for integration into anatomic slices.

RESULTS

Virtual movements of the missing limbs produced contralateral primary sensorimotor cortex and central sulcus activations in the patients with upper-limb amputation. Interhemispheric and bilateral activations were found in the patient with both legs amputated. These activation areas were different from the stump activation areas. Additionally, the significance thresholds chosen to generate the activation maps in virtual movements (although individual) were globally the same as those used to detect motor activation in the normal side of the patients.

CONCLUSION

Cortical areas devoted to the missing limb seem to persist for several years after amputation. The precentral activations found in our patients are in agreement with the statement that the neural mechanisms involved in the mental representation of an action and in its execution are the same. Data from fMRI can be used to evaluate phantom limb virtual movements and to study cortical reorganization phenomena that can appear with time or as a result of some therapies. In these patients, fMRI data may be useful in assisting the neurosurgeon in the placement of chronic motor cortex electrodes.

Phantom pain and phantom sensations in upper limb amputees: an epidemiological study

Phantom pain in subjects with an amputated limb is a well-known problem. However, estimates of the prevalence of phantom pain differ considerably in the literature. Various factors associated with phantom pain have been described including pain before the amputation, gender, dominance, and time elapsed since the amputation. The purposes of this study were to determine prevalence and factors associated with phantom pain and phantom sensations in upper limb amputees in The Netherlands. Additionally, the relationship between phantom pain, phantom sensations and prosthesis use in upper limb amputees was investigated. One hundred twenty-four upper limb amputees participated in this study. Subjects were asked to fill out a self-developed questionnaire scoring the following items: date, side, level, and reason of amputation, duration of experienced pain before amputation, frequencies with which phantom sensations, phantom pain, and stump pain are experienced, amount of trouble and suffering experienced, respectively, related to these sensations, type of phantom sensations, medical treatment received for phantom pain and/or stump pain, and the effects of the treatment, self medication, and prosthesis use. The response rate was 80%. The prevalence of phantom pain was 51%, of phantom sensations 76% and of stump pain 49%; 48% of the subjects experienced phantom pain a few times per day or more; 64% experienced moderate to very much suffering from the phantom pain. A significant association was found between phantom pain and phantom sensations (relative risk 11.3) and between phantom pain and stump pain (relative risk 1.9). No other factors associated with phantom pain or phantom sensations could be determined. Only four patients received medical treatment for their phantom pain. Phantom pain is a common problem in upper limb amputees that causes considerable suffering for the subjects involved. Only a minority of subjects are treated for phantom pain. Further research is needed to determine factors associated with phantom pain.

A passion of the soul: an introduction to pain for consciousness researchers

Pain is an important focus for consciousness research because it is an avenue for exploring somatic awareness, emotion, and the genesis of subjectivity. In principle, pain is awareness of tissue trauma, but pain can occur in the absence of identifiable injury, and sometimes substantive tissue injury produces no pain. The purpose of this paper is to help bridge pain research and consciousness studies. It reviews the basic sensory neurophysiology associated with tissue injury, including transduction, transmission, modulation, and central representation. In addition, it highlights the central mechanisms for the emotional aspects of pain, demonstrating the physiological link between tissue trauma and mechanisms of emotional arousal. Finally, we discuss several current issues in the field of pain research that bear on central issues in consciousness studies, such as sickness and sense of self.

Phantom sensations in a patient with cervical nerve root avulsion

This case study reports detailed phantom sensations in a 35-yr.-old man who had his C5 and C6 cervical nerve roots avulsed from the cord during a motorcycle accident at the age of 22 years. The subject, who was left with a paralyzed right deltoid muscle, anesthetic sensation along the upper lateral portion of the right arm, and absent right biceps reflex, became aware of phantom right arm and hand sensations a few months after the original injury. This finding--which has important implications for understanding the process involved in bodily perception as well as the development of these perceptions--provides evidence of a distributed neural representation of the body that has both genetic and experiential determinants. The implications of these findings are discussed with reference to recent concepts of phantom limb experiences and related phenomena.

On the possibility of universal neural coding of subjective experience

Various neurophysiological experiments have revealed remarkable correlations between cortical neuronal activity and subjective experiences. However, the mere presence of neuronal electrical activity does not appear to be sufficient to produce these experiences. It has been suggested that the explanation for the neural basis of consciousness might lie in understanding the reason that some types of neuronal activity possess subjective correlates and others do not. Here I propose and develop the idea that this difference may be caused by the existence of an elementary nonarbitrary linkage between temporal or spatiotemporal patterns of neuronal activity and their subjective attributes. I also show how cortical neural circuits capable of generating experience-coding patterns could emerge during evolution and brain development, due to the presence of spontaneous stochastic neuronal activity and activity-dependent synaptic plasticity. This hypothesis leads to several testable predictions, principal among which is the idea that the neural correlates of consciousness are essentially innate and universal.

Phantom limb pain: a review of the literature on attributes and potential mechanisms

This study presents a review of the literature on the attributes and potential mechanisms involved in phantom limb pain, encompassing studies describing pain in the residual limb, phantom sensation and phantom limb pain, and the difficulties that may arise when making these distinctions. A variety of theories have been proposed to explain causal mechanisms for phantom limb pain. Conceptually, research into phantom limb pain is informed by the particular theory of chronic pain that is dominant at the time the research is undertaken. For example, early physiological theories on the etiology of phantom limb pain were grounded in specificity or pattern theories of pain. Later physiological research was based on the framework provided by Gate Control Theory and focused on identifying peripheral, spinal, and central neural mechanisms. Psychological explanations were grounded in psychoanalytic or personality theories of chronic pain which propose that phantom limb pain results from pre-amputation psychological disturbance. Despite numerous studies examining phantom limb pain, much of this research has both conceptual and methodological shortcomings. As such, the application of these research findings to clinical practice has limited utility.

Hand-mouth coordination, congenital absence of limb, and evidence for innate body schemas

Studies of phantom limb in cases of congenital (aplasic) absence of limb have provided inadequate evidence concerning the innate neurological substrate responsible for the phantom. In this study we review evidence from ultrasonic and behavioral studies of hand-mouth coordination in utero and in early infancy, neurobiological studies in primates, and studies of neural reorganization following amputation. We suggest two complementary hypotheses to explain aplasic phantoms. First, aplasic phantoms are based on the existence of specific neural circuitry associated with innate motor schemas, such as the neural matrix responsible for early hand-mouth coordination. Second, aplasic phantoms are modified by mechanisms that involve a reorganization of neural representations of the missing limb within a complex network involving both cortical and subcortical structures.

Studies of neuroplasticity with transcranial magnetic stimulation

In recent years, there has been increasing interest in studies of brain plasticity. Although still loosely defined, this term describes the ability of the brain to change. Cortical plasticity encompasses a wide variety of phenomena and mechanisms, including modifications in cortical properties such as strength of internal connections, representational patterns, or neuronal modifications, either morphological or functional (Donoghue et al., 1996). We focus on the description of different ways in which transcranial magnetic stimulation (TMS) can be used to study patterns of reorganization and some of the mechanisms involved in these changes. Correlation between TMS and neuroimaging studies in humans and animal studies addressing similar questions is discussed. It is important to identify in each situation whether plasticity plays a beneficial role or is maladaptive in terms of functional compensation. The understanding of patterns, mechanisms, and functional relevance of cortical plasticity will hopefully lead to the design of effective strategies to enhance plasticity when it is beneficial and to down-regulate it when it is maladaptive. An example of a possible strategy, using TMS, is discussed.

The cortical somatotopic map and phantom phenomena in subjects with congenital limb atrophy and traumatic amputees with phantom limb pain

The extent of the cortical somatotopic map and its relationship to phantom phenomena was tested in five subjects with congenital absence of an upper limb, four traumatic amputees with phantom limb pain and five healthy controls. Cortical maps of the first and fifth digit of the intact hand, the lower lip and the first toe (bilaterally) were obtained using neuroelectric source imaging. The subjects with congenital upper limb atrophy showed symmetric positions of the left and right side of the lower lip and the first toe, whereas the traumatic amputees with pain showed a significant shift (about 2.4 cm) of the cortical representation of the lower lip towards the hand region contralateral to the amputation side but no shift for the toe representation. In healthy controls, no significant hemispheric differences between the cortical representation of the digits, lower lip or first toe were found. Phantom phenomena were absent in the congenital but extensive in the traumatic amputees. These data confirm the assumption that congenital absence of a limb does not lead to cortical reorganization or phantom limbs whereas traumatic amputations that are accompanied by phantom limb pain show shifts of the cortical areas adjacent to the amputation zone towards the representation of the deafferented body part.

The body in the brain: neural bases of corporeal awareness

Recent studies have begun to unravel the brain mechanisms that underlie the mental representation of the body. Imitation of movements by neonates suggests an implicit knowledge of the body structure that antedates the adult body schema. This can include inanimate objects that bear systematic relations to the body, as shown by the elimination from self awareness of a body part and its associated paraphernalia after selective brain lesions. Dynamic aspects of the body schema are revealed by spontaneous sensations from a lost body part as well as by orderly phantom sensations elicited by stimulation of body areas away from the amputation line and even by visual stimulation. The mechanisms of the body schema exhibit stability, since some brain regions seem permanently committed to representing the corresponding body parts in conscious awareness, and plasticity, since brain regions deprived of their natural inputs from a body part become reactive to inputs from other body parts.

Illusory Reduplication of One's Own Body: Phenomenology and Classification of Autoscopic Phenomena

Autoscopic phenomena involve the illusory reduplication of one's own body. The literature on the topic is widely scattered and suffers from considerable terminological and conceptual inconsistencies. This article proposes a classification scheme based on phenomenological criteria. Along with examples of illustrative cases, we outline the main features of autoscopic hallucinations, heautoscopy proper, the feeling of a presence, the out-of-body experience, and negative and inner forms of autoscopic phenomena. We also discuss the need for a differentiation of autoscopic phenomena from reduplicative paramnesias and the misidentification syndromes. Finally, the concept of a neuromatrix (Melzack, 1990) is proposed as a starting point for the understanding of the neuronal mechanisms underlying autoscopic phenomena.

The earliest sense of self and others: Merleau-Ponty and recent developmental studies

Recent studies in developmental psychology have found evidence to suggest that there exists an innate system that accounts for the possibilities of early infant imitation and the existence of phantom limbs in cases of congenital absence of limbs. These results challenge traditional assumptions about the status and development of the body schema and body image, and about the nature of the translation process between perceptual experience and motor ability. Merleau-Ponty, who was greatly influenced by his study of developmental psychology, and whose phenomenology of perception was closely tied to the concept of the body schema, accepted these traditional assumptions. They also informed his philosophical conclusions concerning the experience of self and others. We re-examine issues involved in understanding self and others in light of the more recent research in developmental psychology. More specifically our re-examination challenges a number of Merleau-Ponty's conclusions and suggests, in contrast, that the newborn infant is capable of a rudimentary differentiation between self and non-self.