The Effect of the Rubber Hand Illusion on Sensory Thresholds

The rubber hand illusion (RHI) causes a change in body perception and awareness as a result of the integration of simultaneously perceived visual and tactile stimulation. In the rubber hand illusion (RHI), which was first described in 1998, a realistic hand model is perceived as a part of the body and body awareness is impaired. In the RHI, the participant's real hand is positioned behind a screen so that it is out of sight; The rubber model hand is placed in the field of vision and in the appropriate position with the real hand. Brush is applied simultaneously to the same parts of the real and rubber hands. He/she perceives the rubber hand as his own and the brush starts to feel as if it is being rubbed into his own hand. This method, which causes the illusion of body belonging, has been defined as the rubber hand illusion. During the rubber hand illusion, increased activity was observed in the ventral premotor cortex, infraparietal cortex and cerebellum in functional MRI. It is suggested that this phenomenon occurs with the integration of interrelated visual, tactile and proprioceptive senses reaching the premotor cortex. Quantitative sensory tests are standardized subjective clinical sensitivity tests that require the collaboration of the person to be examined. In the tests, calibrated stimuli are applied to capture perception and pain thresholds, thus providing information about sensory thresholds. The impairment of body perception caused by RHI contributes to the multi-faceted understanding of sensory perception, higher-level cognitive processes, brain mapping and functions. In the studies; It has been suggested that the conflict between visual and proprioceptive sensory information created during the rubber hand illusion is resolved by the attenuation of somatosensory input at the cortical level. As far as we know, tactile sensory threshold from quantitative sensory tests, two-point discrimination from cortical senses, pressure pain threshold measured by the algometer, and vibration threshold variation during and after rubber hand burning, which causes changes in body perception, have not been studied before. In this study, the relationship between the RHI phenomenon and sensory thresholds will be evaluated.

Tactile sensory threshold from quantitative sensory tests, two point discrimination from cortical senses, pressure pain threshold measured by algometer will be examined during and after the rubber hand burning, which causes changes in body perception.

Semmes-Weinstein monofilaments (SWM) are widely used for reproducible testing and measurement of tactile sensory threshold. The sizes of Semmes-Weinstein monofilaments increase on a logarithmic scale. It is made with nylon (line) monofilaments of approximately the same length. To apply, monofilaments are kept perpendicular to the skin and brought into contact. When the pressure is increased and the end point of the filament reaches the forcing threshold, the filament bends. Even if pressure is continued after the filaments are bent, there is no increase in the pressure felt on the skin. For this reason, when the monofilaments are inclined, since no more pressure can be applied with that filament, it is questioned whether the patient is felt or not. Three applications should be made to the patient with the same filament.

Two point discrimination (TPD) is the ability to distinguish between two points that are brought into contact with the skin at the same time and with the same pressure, that they are actually two separate points, not one. It was described by Ernest Heinrich Weber (1846). Blunt tip static and mobile TPD is usually tested using Disk-Criminator. Two points are brought into contact with the skin with a compass-like instrument or a compass. It can randomly switch between touching and touching a point or two points in the area being tested. The person being tested is asked to say how many points he felt. The smallest distance resulting in the perception of two different stimuli is recorded as the patient's two point discrimination threshold.

Pain pressure threshold is defined as the minimum pressure value that creates a perception of pain. The test determines the amount of pressure in a particular area as soon as an ever-increasing painless pressure stimulus turns into a painful feeling of pressure. The pressure algometer (dolorimeter) used for this test is a device used to evaluate sensitivity to pain. The mechanical method using the pressure sensor provides ease of use, is harmless to the patient, and has acceptable reliability and repeatability. Light pressure is applied to the body area to be tested with the algometer. The intensity of the pressure is increased gradually. The participant is asked to say the moment he feels the sensation of pain instead of pressure during the algometric measurement. The amount of pressure that causes pain is recorded as the pressure pain threshold (PPT) in kg / cm2. It has been shown that 3 measurements are required to maximize measurement properties.

Inclusion Criteria: Healthy 18-65 years old age Exclusion Criteria: Neuropathy Presence of any known neurological or psychiatric disease Inability to cooperate with the tests to be performed Amputation and nerve damage in the upper extremities Upper extremities dysfunction due to nerve damage

Since the study is planned as a specialist thesis, the details of the study can be shared by the faculty administration.

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