Biological Psychology Practical Class 4: Proprioception PDF

4. Proprioception (joint position sense and balance) Proprioception refers to our ability to perceive the position and movement of our body parts, to localize ourselves in space, and to sense force, heaviness and the tension of our muscles from an internal perspective (i.e., in the absence o...

4. Proprioception (joint position sense and balance) Proprioception refers to our ability to perceive the position and movement of our body parts, to localize ourselves in space, and to sense force, heaviness and the tension of our muscles from an internal perspective (i.e., in the absence of visual information). We can feel the position of our hands even with eyes closed; we are able to touch our nose with our index finger - this task is often used by doctors to assess if proprioception is still intact. Certain mechanoreceptors, dubbed proprioceptors, form the basis of this sense. They are located primarily in our locomotor system: muscle spindle receptors are sensitive to stretching, Golgi tendon organs respond to the tension of the tendons, and joint receptors signal the actual position of joints. Moreover, mechanoreceptors in our skin and centrally generated signals, such as the sense of effort (also called efferent copy), that is used to predict the consequence of the motor command, can also contribute to proprioception. The importance of proprioception is demonstrated clearly by studying patients whose nerves that carry proprioceptive afferent information are damaged. They lose the ability to control their movements smoothly and properly, even when visual information is available. In the absence of visual information, they are totally unaware of the position of their limbs. From a psychological perspective, they often feel that their body is not theirs anymore, i.e., they loss the sense of ownership. Information originating from proprioceptors is utilized at different levels of movement control, from elementary automatic responses (e.g. the knee jerk reflex) to more complex automatic and conscious (intentional) regulation. In the latter cases, it typically becomes integrated with information from other sensory modalities. For example, keeping the balance when standing on one leg requires such integration. We rely on visual information to a great extent (the task is more difficult with closed eyes), but vestibular, proprioceptive and even tactile input from the soles is also used. Balancing ability can also be assessed by measuring how well one can keep a stable posture, often without visual information, and/or on an unstable surface on two legs (Fig 4.1). Balancing ability is an important factor of motor functioning, and a predictor of sport performance and fall-related injuries of elderly people. Fig 4.1. Various assessments of the ability to maintain a stable standing posture; (from left to right): (standard) integration of all available information; (proprioception) relying mainly on proprioceptive input (including tactile information from the soles); (vision) relying mainly on visual information (blurred tactile input); (vestibular) relying primarily on vestibular information (no visual input and blurred tactile input). Source (including normative data): https://balancetrackingsystems.com/wp-content/uploads/2020/06/BTS-Normative-CTSIB-Data- 2020.pdf Also, integration of information from different sensory modalities can be demonstrated with the so-called rubber hand illusion (RHI). To evoke the illusion, the experimenter covers one of the participants' hand, and places a rubber hand in front of the participant, visually replacing the real hand. Then the seen rubber hand is stimulated (i.e. stroked with a paintbrush) at the same time and in the same place as the unseen real hand (Fig 4.2). Because of the synchrony of tactile and visual information, most of the participants will report a modification in the feeling of body ownership: they feel that the rubber hand is their own hand, whereas body ownership with respect to their own hand becomes lost. In other words, synchronous tactile and visual information can overwrite proprioceptive information. 2 Fig 4.2. Basic experimental setup for the evokation of the rubber hand illusion. Synchronous stimulation of the unseen real hand and the seen rubber hand can lead to the feeling that the rubber hand is the own hand (replacement of body ownership). Source: de Haan, A. M., Van Stralen, H. E., Smit, M., Keizer, A., Van der Stigchel, S., & Dijkerman, H. C. (2017). No consistent cooling of the real hand in the rubber hand illusion. Acta Psychologica, 179, 68–77. A proportion of proprioceptive information reaches conscious awareness. If we focus on our body, for example when learning a new motor skill, we can perceive proprioceptive information. However, there are considerable individual differences in the acuity of this perception, which is called proprioceptive accuracy. This ability can be measured in various ways. One of the most widely used methods is the joint position reproduction test, where the joint/body part is guided to a certain position, and one has to reproduce this position with the same or with the contralateral body part with eyes closed (Fig 4.3). There are other techniques, such as measuring ones' ability to detect passive motion, or assessing how accurately one is able to reproduce or discriminate between different levels of force, muscle tension, movement velocity and trajectory, and the weight and size of different objects. Proprioceptive accuracy is positively associated with motor performance. It deteriorates with aging, and is compromised in many movement disorders (e.g. Parkinson’s disease, cerebral palsy). Measuring proprioceptive accuracy can be an important tool for sport selection and for assessing the risk of fall-related and sport injuries. One can improve proprioceptive accuracy with proprioceptive training, that results in an improved movement regulation. Thus, proprioceptive training is often utilized in the field of rehabilitation and athletic training. 3 Fig 4.3. A simple device for the assessment of proprioceptive accuracy with respect to the elbow joint. Presented position (angle) must be reproduces with the same or with the contralateral arm. From a psychological perspective, proprioceptive input plays an important role in the emotional experience too. Concerning the actual position of multiple joints, taking different body positions can result in a change in the emotional state. For example, an expansive body pose (i.e. power posing) can result in an improved self-reported feeling of power, and even behavioral and hormonal changes. With reducing muscle tension, which is an important part of many relaxation techniques (e.g. autogenic training, progressive relaxation; see also Chapter 3), stress and anxiety can be reduced. Also, the activation of arm flexor muscles, that are associated with approaching objects, results in a more positive judgement of neutral stimuli. In a similar vein, activating arm extensor muscles is associated with avoiding objects, and results in a more negative judgement of neutral stimuli. Goals of the class: Demonstration of the rubber hand illusion, the assessment of proprioceptive accuracy (knee and/or elbow joint) and balance (BTracksSTM BalancePlate system) 4