a neuroscientific view of the effect of vestibular dysfunction on bodily self-consciousness

A NEUROSCIENTIFIC VIEW OF THE EFFECT OF VESTIBULAR

DYSFUNCTION ON BODILY SELF-CONSCIOUSNESS

Scientific background and a case for physical therapy management of affected patients

Nathan Dugan 3rd Year PT Student Columbia University

Goals

1.  Present the concept of body schema and body image, and how they play into the greater idea of “bodily self-consciousness”

2.  Present clinical information relating to “non-traditional” symptoms of an insult to the vestibular system

3.  Provide an experimental basis for conclusions and a hypothesis relating to the effect of vestibular dysfunction on various aspects of bodily self-consciousness from a neuroscientific perspective

4.  Provide information that is beneficial to determine patients who may benefit from vestibular rehabilitation and/or exercises, based on certain signs and symptoms that are not traditionally thought of as being related to vestibular dysfunction

Outline

■  Definitions ■  Distorted body schema and body image ■  Sense of unity between the self and the body ■  Agency ■  Depersonalization and derealization ■  Conclusion

BODY SCHEMA VERSUS BODY IMAGE

■  Body Schema –  “…a system of sensory-motor processes that constantly

regulate posture and movement…” –  “…a collection of sensory-motor interactions that individually

define a specific movement or posture…” –  Function without reflective awareness or a need for

conscious monitoring ■  Body Image –  “…a (sometimes conscious) system of perception, attitudes,

beliefs, and dispositions pertaining to one’s own body.” –  Involves body percept, body concept, and body affect

Source: Gallagher, 2005

■  Body Percept (primary, conscious) –  “…subject’s perceptual experience of his/her own

body” ■  Body Concept –  “…subject’s conceptual understanding (including

folk and/or scientific knowledge) of the body in general” ■  Body Affect –  “…subject’s emotional attitude toward his/her own

body”


■  Interplay between body schema and body image is important for understanding concept

Example: Catching a baseball hit to the outfield during a baseball game

Conscious awareness is directed towards ball, while bodily movement continues to occur in smooth and coordinated fashion (body schema)

Example: Learning a novel dance step

Attention is paid to visual, proprioceptive, and tactile inputs to consciously monitor and correct movement (body image), however unconscious processes (body schema) continue to occur to maintain balance and enable movement


DISTORTED BODY SCHEMA AND BODY IMAGE

Clinical description, experimental evidence, and neurophysiological hypothesis

Clinical Description

■  Vestibular contribution to body schema/image postulated as early as 1893

–  Bonnier described example of patient who “felt his head became enormous, immense, losing itself in the air; his body disappeared and his whole being was reduced to only his face”

–  Schilder described vestibular patients who endorsed feeling that their “neck swells during dizziness,” “extremities had become larger,” “feet seemed to elongate”

■  These symptoms (evoked by vestibular dysfunction) are comparable to asomatognosia seen in other neurological syndromes

Source: Lopez, 2013; Diequez, 2007

Experimental Evidence

■  All based on effects of caloric (CVS) and galvanic (GVS) vestibular stimulation on perceived shape/size of body

■  Examples: –  Patient with Wallenberg’s syndrome, reported macrosomatognosia to

left hemiface ■  CVS temporarily alleviated this perception

–  CVS provoked phantom limb perception in amputees –  CVS modified perception of left hand – it was perceived as larger than

it was ■  Detailed on next slide

Source: Lopez, 2013

Vestibular Stimulation

Modifies the Body Schema

Source: Lopez, 2012

Vestibular Stimulation Modifies the Body Schema – Results & Conclusions ■  Results –  Experiment 1: ■  Higher occurrence of perception of hand being longer during CVS compared to sham ■  During CVS, participants reports feeling “’spacy’ – being detached from their own body and

the surroundings, and “not being in control of their self” –  Experiment 2: ■  Significant increase in perceived length and width of left hand during CVS ■  Stronger changes in bodily perceptions (“body feels strange or different in some way”)

■  Conclusions –  Vestibular signals influence the body schema in healthy participants

Source: Lopez, 2012

Neurophysiological Hypothesis

■  Mechanism –  Abnormal vestibular signals arriving to brain cortex may interfere with

somatosensory processing at multimodal areas ■  For example, misinterpretation of postural signals from neck may explain reports of neck

feeling “enlarged”

–  That CVS/GVS produce similar results (perceived enlargement of body parts) in healthy subjects is support of theory

Source: Lopez, 2013

SENSE OF UNITY BETWEEN THE SELF AND

THE BODY Clinical description, experimental evidence, and neurophysiological

hypothesis


■  Out-of-Body Experience (OBE) –  Full-blown, clear cases linked to vestibular dysfunction are rare –  Bonnier described “it seemed to [the patient] that he was divided into

two persons, one who had not changed posture, and another new person on his right, looking somewhat outwardly. Then the two somatic individuals approached each other, merged, and the vertigo disappeared”

–  Skworzoff described that, “one patient saw herself for a moment in the daylight,” another patient “saw and felt every day his own double” and also reported sensations of flying

Source: Lopez, 2013


■  GVS creates a perceived motion in the absence of physical motion –  This then represents a dissociation between perceived self-location and physical

body location ■  Proposed that this represents partial disembodiment similar to OBE in neurological disorders

■  Indirect evidence of vestibular contribution: –  OBE more frequent in persons who are lying down (73%) ■  Suggests contribution of vestibular gravitational signals

Source: Lopez, 2013


■  Mechanism (leading to OBE) –  “Triple Sensory Misintegration” –  Support for model: ■  Vestibular symptoms often in OBE caused by neurological disorder –  Brain areas often damaged in these patients overlap with vestibular cortex

–  In vestibular dysfunction: ■  May be due to sensory mismatch created by vertigo attacks

Source: Lopez, 2013

AGENCY Clinical description, experimental evidence, and neurophysiological

hypothesis


■  Many patients with vestibular dysfunction report experience of “not being in control of their self”

■  Often report that their actions do not match their intentions

■  Patients may perceive instability and dizziness despite not exhibiting evident signs of postural imbalance

Source: Lopez, 2013


■  Role of vestibular signals relating to agency has not been specifically tested

■  In healthy subjects: –  CVS evoked feeling of “not being in control of the self” –  GVS altered ability to perform and predict hand movements

Source: Lopez, 2013


■  Altered sense of agency may be due to vestibular organs incorrectly encoding consequences of actions

■  Patients tend to: –  Underestimate body displacements –  Misinterpret direction of body movements ■  Reveals crucial role of vestibular signals in spatial updating during whole-body motion

■  Agency based on congruent sensory feedback from one’s actions

■  Vestibular dysfunctions likely to produce spatiotemporal mismatch between motor commands and feedback from action

Source: Lopez, 2013

DEPERSONALIZATION AND DEREALIZATION (DD)

Clinical description, experimental evidence, and neurophysiological hypothesis


■  Encompasses previous sections

■  Patient descriptions: –  “I feel like I’m outside myself. I feel like I’m not in myself.” –  “I am not actually being there or having anything to do with my body.” –  Also report sensations of “deja-vu,” “body feels strange,” feeling “spacy” or “spaced-

out”

Source: Lopez, 2013


■  In healthy subjects –  CVS increased frequency of: ■  “Surroundings seem strange and unreal” ■  “Time seems to pass very slowly” ■  “Body feels strange/different in some way”

Source: Lopez, 2013


■  “Discrepancy between vestibular and other body-related signals may deteriorate the experience of the body and surroundings, leading to DD”

■  Various sensory dysfunctions (vestibular, visual, auditory) increase DD symptoms

■  PET study showed that DD related to same brain regions activated by CVS/GVS

■  Shown that vestibular neuritis alters metabolism in “very similar” brain regions

■  “This anatomical overlap strongly suggests that vestibular dysfunction disorganizes brain metabolism, multisensory integration, and eventually structure and connections in the multisensory temporoparietal cortex, and this may be the underlying mechanism of DD in vestibular patients”

Source: Lopez, 2013

CONCLUSIONS

QUESTIONS?

References

1)  Gallagher S. How the body shapes the mind. New York, NY: Clarendon Press; 2005.

2)  Lopez C, Schreyer H-M, Preuss N, Mast FW. Vestibular stimulation modifies the body schema. Neuropsychologica. 2012;50:1830-1837.

3)  Lopez C. A neuroscientific account of how vestibular disorders impair bodily self-consciousness. Frontiers in Integrative Neuroscience. 2013;7(91):1-8.

4)  Dieguez S, Staub F, Bogousslavsky J. (2007). “Asomatognosia,” in The Behavioral and Cognitive Neurology of Stroke, eds J. Bogousslavsky and O. Godefroy (New York:Cambridge University Press), 215–253.

a neuroscientific view of the effect of vestibular dysfunction on bodily self-consciousness

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