The homuncular jigsaw: investigations of phantom limb and body awareness following brachial plexus block or avulsion

Many neuropsychological theories agree that the brain maintains a relatively persistent representation of one's own body, as indicated by vivid "phantom" experiences. It remains unclear how the loss of sensory and motor information contributes to the presence of this representation. Here, we focus on new empirical and theoretical evidence of phantom sensations following damage to or an anesthetic block of the brachial plexus. We suggest a crucial role of this structure in understanding the interaction between peripheral and central mechanisms in health and in pathology. Studies of brachial plexus function have shed new light on how neuroplasticity enables "somatotopic interferences", including pain and body awareness. Understanding the relations among clinical disorders, their neural substrate, and behavioral outcomes may enhance methods of sensory rehabilitation for phantom limbs

Disconnected body representation: neuroplasticity following spinal cord injury

Neuroplastic changes in somatotopic organization within the motor and somatosensory systems have long been observed. The interruption of afferent and efferent brain-body pathways promotes extensive cortical reorganization. Changes are majorly related to the typical homuncular organization of sensorimotor areas and specific "somatotopic interferences". Recent findings revealed a relevant peripheral contribution to the plasticity of body representation in addition to the role of sensorimotor cortices. Here, we review the ways in which structures and brain mechanisms react to missing or critically altered sensory and motor peripheral signals. We suggest that these plastic events are: (i) variably affected across multiple timescales, (ii) age-dependent, (iii) strongly related to altered perceptual sensations during and after remapping of the deafferented peripheral area, and (iv) may contribute to the appearance of secondary pathological conditions, such as allodynia, hyperalgesia, and neuropathic pain. Understanding the considerable complexity of plastic reorganization processes will be a fundamental step in the formulation of theoretical and clinical models useful for maximizing rehabilitation programs and resulting recovery

Go virtual to get real: virtual reality as a resource for spinal cord treatment

Abstract: Increasingly, refined virtual reality (VR) techniques allow for the simultaneous and coherent stimulation of multiple sensory and motor domains. In some clinical interventions, such as those related to spinal cord injuries (SCIs), the impact of VR on people′s multisensory perception, movements, attitudes, and even modulations of socio‐cognitive aspects of their behavior may influence every phase of their rehabilitation treatment, from the acute to chronic stages. This work describes the potential advantages of using first‐person‐perspective VR to treat SCIs and its implications for manipulating sensory‐motor feedback to alter body signals. By situating a patient with SCI in a virtual environment, sensorial perceptions and motor intention can be enriched into a more coherent bodily experience that also promotes processes of neural regeneration and plasticity. In addition to the great potential of research, the most significant areas of interest concern is managing neuropathic pain, motor rehabilitation, and psychological well‐being

Rethinking the Body in the Brain after Spinal Cord Injury

Spinal cord injuries (SCI) are disruptive neurological events that severly affect the body leading to the interruption of sensorimotor and autonomic pathways. Recent research highlighted SCI-related alterations extend beyond than the expected network, involving most of the central nervous system and goes far beyond primary sensorimotor cortices. The present perspective offers an alternative, useful way to interpret conflicting findings by focusing on the deafferented and deefferented body as the central object of interest. After an introduction to the main processes involved in reorganization according to SCI, we will focus separately on the body regions of the head, upper limbs, and lower limbs in complete, incomplete, and deafferent SCI participants. On one hand, the imprinting of the body’s spatial organization is entrenched in the brain such that its representation likely lasts for the entire lifetime of patients, independent of the severity of the SCI. However, neural activity is extremely adaptable, even over short time scales, and is modulated by changing conditions or different compensative strategies. Therefore, a better understanding of both aspects is an invaluable clinical resource for rehabilitation and the successful use of modern robotic technologies

Abstraction still holds its feet on the ground

In view of current scientific knowledge, it seems premature to hypothesize a qualitative distinction between processes, networks, and structures involved in abstract processes from those based on perception, episodic, or procedural memories. Predictive thought and mental travel strongly rely, at different levels of consciousness, on past and ongoing sensory input, bodily information (e.g., interoception), and the results of perceptual elaboration

Come lo strumento diventa me

«Embodiment» is a term that highlights how our sense of the body is plastic and can be extended beyond the biological self to incorporate a salient tool. Theoretical bases are grounded in the widely discussed concepts of embodiment, tool use, and body representation. To support these claims, we will first explore highlight a pathway in the confusing scenario of the consequences of dynamic bodily representations. The primary interest is to explore the potentialities of embodiment, and to assess human experiences that can be directly measured concerning partial or complete bodily illusions. Next we will focus on tools and their classification criteria, identifying theoretically useful and clear relationships between technology and the body. The third part of the paper will capture the occurrences of unique identifiable experiences of the body tool and perceptual and motor disabilities. The aim is to propose some points of view about the implications for the incorporation of an external assistive device in the representation of a «new» sense of one's own body. Empirical evidence supports the argued topics, suggesting that the facilitation of embodiment processes that use tools, prostheses, and other technological devices is synthesized from complex multisensory mechanisms that find their bases both in the person and the object. Following this path, clinical research will face the need to understand the exact mechanisms involved in improving the embodiment of sophisticated biotechnologies combining multidisciplinary studies

Integrated Neuroregenerative Techniques for Plasticity of the Injured Spinal Cord

On the slow path to improving the life expectancy and quality of life of patients post spinal cord injury (SCI), recovery remains controversial. The potential role of the regenerative capacity of the nervous system has led to numerous attempts to stimulate the SCI to re-establish the interrupted sensorimotor loop and to understand its potential in the recovery process. Numerous resources are now available, from pharmacological to biomolecular approaches and from neuromodulation to sensorimotor rehabilitation interventions based on the use of various neural interfaces, exoskeletons, and virtual reality applications. The integration of existing resources seems to be a promising field of research, especially from the perspective of improving living conditions in the short to medium term. Goals such as reducing chronic forms of neuropathic pain, regaining control over certain physiological activities, and enhancing residual abilities are often more urgent than complete functional recovery. In this perspective article, we provide an overview of the latest interventions for the treatment of SCI through broad phases of injury rehabilitation. The underlying intention of this work is to introduce a spinal cord neuroplasticity-based multimodal approach to promote functional recovery and improve quality of life after SCI. Nonetheless, when used separately, biomolecular therapeutic approaches have been shown to have modest outcomes

My hand in my ear: a phantom limb re-induced by the illusion of body ownership in a patient with a brachial plexus lesion

Corporeal awareness of body unity, continuity, and integrity is hardwired in the brain, even following massive deafferentation. Following peripheral limb injury, referred phantom sensations are reported frequently on the cheek and, rarely, on the ear. Here, we explore how brain plasticity mechanisms induced by multisensory stimulation of different facial regions (cheek and ear) modulate the feeling that a complete missing limb is still attached to the body. We applied the modified rubber hand illusion (RHI) paradigm following synchronous and asynchronous stimulation of the face-hand and ear-hand in the unusual case of a patient with a brachial plexus lesion, who had lost upper-left limb sensation and developed a phantom sensation of the arm restricted to the ear. He experienced a strong illusion of ownership of the rubber hand during synchronous stroking of the ear but not the cheek and reported more defined tactile sensations in his previously numb body part during the illusion than when simply touching the ear. Phantom experiences are not exclusively based on sensory memories of the once-present body periphery, they are organized into a topographic cortical map with the ear-hand area adjoining but separate from the face. Multimodal experiences specifically modulate possible remapping of ear-hand representations and generate a more defined connection between the brain's memory of the body and what one feels of the actual physical body. We suggest that RHI is a form of sensory intervention that makes the best use of residual signals from disconnected body parts after peripheral injury, evoking and controlling the limb sensations

Rebuilding the body from the inside: interoception and the bodily self following spinal cord injuries

Spinal cord injury (SCI) significantly impacts body awareness by disrupting brain-body communication. Attempts have been made to enhance the sense of self-identification with the body post-SCI by intervening at a multisensory level. However, the contribution of the interoceptive domain remains largely unaddressed. We explored the role of interoception in modulating the sense of body ownership following high or low thoracic SCI. This distinction allowed us to discriminate in terms of visceral and cardiac interoceptive afferents spared. We selected male participants in the chronic phase of the disease divided into two groups: 15 patients with T1-T4 lesions, mean age 33 ± 7 years, mean time since lesion 869 ± 512 days; 15 patients with T8-T12 lesions, mean age 36 ± 8 years, mean time since injury 906 ± 479 days. The level of the neurological lesion was determined by using AIS grade. Exclusion criteria were the presence of brain injury, head trauma, neurological, cardiovascular, or psychiatric diseases. Our procedure included physiological, behavioural and metacognitive measurements. Body ownership changes were assessed using the Rubber Hand Illusion (RHI) paradigm (comprising RHI questionnaire and proprioceptive drift assessment) with simultaneous recording of cardiac activity. The interoceptive accuracy index was obtained via the Heartbeat Tracking Task. Then, the degree of interoceptive awareness was rated using a 10-point VAS (0=no heartbeat awareness, 10=full awareness). The Cambridge Depersonalisation Scale (CDS) was used to investigate the presence of any symptoms of depersonalisation or derealisation. The Group T1-T4 exhibited:stronger proprioceptive drift (F (1,28) =6.2, p=0.02*ŋp2 >0.18);reduced interoceptive accuracy (z(15)=3.73, p=0.0001); higher CDS scores (z=-2.47, p=0.014). Interoceptive accuracy correlated negatively with CDS score. Our data revealed a link between autonomic completeness and the level and severity of SCI. We exclude that our findings depend on impaired proprioception or posture. No differences were found between the two groups in global body ownership, but patients in the T1-T4 group were more sensitive to multisensory stimulation of the RHI than those with low lesions. As the bodily experience relies on various signals, several factors may be at play, ranging from vision to interoception. Enhancing interoceptive information thus will be the next step in enhancing and normalising the bodily experience post-SCI

An interoceptive perspective of time perception in spinal cord injury

How implicit aspects of time perception can be related to interoception remains still relatively unexplored. Interoceptive states of the body would create our experience of duration. The physiological sense of time would thus be associated with the temporal integration of signals from the interoceptive system. Here, we investigate and relate changes in temporal expectation and interoception in cases of brain-body disconnection. 32 participants with spinal lesions (age range: 19-46 years) in the chronic injury phase were grouped according to level of spinal cord lesion, resulting in two groups: 16 patients with cervical lesion and 16 patients with thoracic lesion. Interoceptive accuracy was measured using a heartbeat tracking task consisting of four trials with varying interval durations of 25, 35, and 45 seconds played in a randomized order. Participants were instructed to internally count the heartbeats they perceived and report the number at the end of each trial. The actual number of heartbeats was measured using electrocardiographic signal. Physiological sense of time was measured using temporal expectation task (TT) and controlled by a color control task (CT). Briefly, a white circle (diameter:12.8degrees of visual angle) was shown on a gray background, with a gray annulus superimposed at an eccentricity of 6.4 - 9.6 degrees of visual angle, acting as an occluding band. In each trial, a purple ball moved from the center of the display toward the periphery in a fixed direction and at a constant speed. In the TT, participants were then asked whether the ball re-emerged earlier or later than expected. In the CT, participants assessed whether the ball reappeared more reddish or bluish than before. The Mann-Whitney U test indicated that the cervical lesion group shows lower interoceptive accuracy than the thoracic lesion group (p < 0.01). Therefore, higher deafferentation in SCI patients can decrease interoceptive accuracy. Interoceptive accuracy was also significantly correlated with the difficulty in temporal (0.69; p<0.002) but no control color task (p<0.17) as discriminated by temporal offsets. Our findings suggest that a reduced interoceptive accuracy play a role in the subjective perception of time in participants with higher SCI lesions. The predictive nature of our temporal task is closely related to the predictive feelings depending on bodily signals. Thus, a lower ability to detect and update the interoceptive inputs seems to reflect a distortion in perceiving pulses emitted by the “pacemaker” of the human internal clock. Alignment of interoceptive and temporal dimensions is consistently with the theoretical framework of the embodied models of timing