The phenomenology of body image distortions induced by regional anaesthesia

Abstract

Patients with peripheral nerve or spinal cord lesions frequently report perceptual distortions related to position, shape, texture or temperature of the affected areas. This study aimed to describe the phenomenology of such body image alterations during the course of upper limb, lower limb or spinal anaesthetic blocks in patients (n = 36) undergoing orthopaedic surgery. Multimodal sensory testing and assessment of motor function were performed at regular intervals, and the relationship between the reported body image distortions and the progression of sensory and motor impairment was analysed. We found that perceptual changes concerning the shape and size of the deafferented limb occurred in the great majority of patients. In all of them, illusions of swelling, elongation or shortening of the limb coincided with the impairment of warm, cold and/or pinprick sensations, suggesting that thin myelinated Adelta- and/or unmyelinated C-fibres may provide a source of tonic modulation to the limb's cortical representation. Such perceptual alterations of shape and size of body parts differed clearly from postural illusions in terms of frequency, time course and influence of vision. In addition to perceptual changes in the deafferented area, almost half of the patients felt their unanaesthetized lips and/or mouth swelling during the course of upper limb block, suggesting the unmasking of dynamic interactions between somatotopically adjacent cortical representations. Conflicting sensations could co-exist in the patient's body image, such as the illusion of swelling of a limb, which, at the same time, was felt to be missing. The sense of ownership of the deafferented limb was impaired in some cases. These observations show that the perception of body shape and the awareness of its postural variations are built from different plastic models. They also underline the contribution of peripheral afferent activity to the maintenance of a unified body image.

More than skin deep: Body representation beyond primary somatosensory cortex

“…This is in contrast to the nearly instantaneous modulations of perceived body form induced by acute deafferentation following cutaneous anaesthesia (Gandevia & Phegan, 1999;Paqueron et al, 2003;Türker, Yeo, & Gandevia, 2005), or proprioceptive illusions (Ehrsson et al, 2005;Lackner, 1988;de Vignemont et al, 2005a). It is not clear why acute deafferentation should have more striking effects on the body image than chronic deafferentation.…”

“…It is not clear why acute deafferentation should have more striking effects on the body image than chronic deafferentation. Nevertheless, such findings suggest that vision is not entirely dominant in the formation of the conscious body image, which appears to reflect a combination of several Body Beyond SI 22 sources of input, including proprioceptive and tactile afferent inputs (e.g., Lackner, 1988) as well as thermal and nociceptive ones (e.g., Paqueron et al, 2003).…”

Embodiment, ownership and disownership

“…But in Paqueron and coll (2003), only 5 out of 36 subjects denied the ownership of their limb (Paqueron et al 2003). …”

Inducing out-of-body experiences

“…69−71 Also, temporary peripheral nerve block in neurologically healthy subjects can lead to a transiently impaired sense of ownership of the deafferented limb in spite of residual perception of position or posture or residual sensations of this limb. 72 Although weightlessness cannot be simulated in a laboratory, other techniques might be used to modulate vestibular and other sensory input and interfere with the subject's orientation regarding body position in space. For instance, mental relaxation techniques leading to a sense of lightness and floating might be used to modulate vestibular, proprioceptive and tactile processing (relaxation).…”