What is Somatosensation?
Somatosensation is the detection, discrimination and recognition of body sensations. Somato- comes from the Greek word “sôma, meaning “body”. It includes sub-modalities of touch sensation, such as light touch (e.g. on the surface of the skin), vibration, firm pressure and texture discrimination; proprioception, involving sensing the location and movement of body parts; and temperature sensation and nociception (the experience of pain contributes towards an adaptive function of danger detection).
The experience of sensing often involves a more complex integration of somatosensory inputs (e.g. haptic recognition of objects) or somatosensory and emotional components (e.g. pain) and may be influenced by emotional and social contexts (e.g. perception of tickle).
Sensation for Perception and Action
Sensory perception is part of our conscious experience of who we are in our environment. As human beings, without touch we cannot process the world around us. Body sensations allow us to be aware of ourselves in our own environment and make quick decisions. It allows us to perceive, explore, and interact with our environment and others, to experience pleasure and to be alerted to danger.
Sensation is important for action. The important role of sensation in motor function is particularly evident in: control of pinch grip; ability to sustain and adapt appropriate force without vision; object manipulation; combining component parts of movement such as transport and grasp; discrimination of surfaces at end of hand held objects; restraint of moving objects; and adjustment to sensory conflict conditions e.g. rough surface. Moreover, the affected limb may not be used spontaneously, despite adequate movement abilities. This may contribute to a learned non-use of the limb and further deterioration of motor function after stroke.
Sensory Impairment after Stroke
One in two people experience loss of body (somatic) sensations after stroke. The loss experienced may vary from a complete loss of all body sensations in one half of the body to difficulty with discriminating one type of sensory information, such as texture discrimination in one body part. Deficits in the discrimination and interpretation of sensory stimuli such as textures, objects and knowledge of limb position are most typical and frequently persist for many years after stroke. Some individuals may experience a hypersensitivity to touch associated with the site of lesion or that develops over time with recovery and neural growth.
Impact of sensory loss – The Lived Experience
The impact of sensory loss is best appreciated through the words of individuals who have experienced it. Rawina is a mother of two who had a stroke shortly after giving birth to her second child. Below Rawina is being interviewed using a standard depression scale rating scale. Rawina’s responses provide some insight into what it might be like to experience loss of touch sensation after stroke.
The importance of the sense touch and ongoing impact of losing that sense on one’s daily life are evident from the individual comments below:
“I may look ok and but feel all left…..and half lost”
“My right side cannot discriminate rough, smooth, rigid, or malleable, sharp or blunt, heavy or light etc. it cannot tell whether that which touches it is a hand or a tennis racket”.
“The dullness of sensation and absence of knowledge of my body’s right sided parameters .. make it frustratingly difficult to control or feel relaxed about any right sided movement”
Please see further explanations from stroke survivors of the experience of sensory loss at the Stroke Foundation enable me site:
https://enableme.org.au/en/Resources/Vision-and-senses
https://enableme.org.au/Community/Podcasts/Sensation
Sensation in the context of occupation
Our senses are part of who we are and how we perceive and interact with our environment. Given the central role of sensation in perception and action, one can appreciate how sensory capacities, or their loss, may affect a person’s occupational performance, participation, and well-being (Carey, 2014). People with sensory loss may have trouble with a range of routine daily tasks such as dressing (e.g., doing up buttons), using a fork, cooking, making a bed, money handling, using a computer, walking on uneven ground, driving, and many other daily activities.
The impact of sensory loss on hand function, performance of daily activities, and return to previous life activities may be assessed in several ways. This may include using the Hand Function Survey (Blennerhassett et al., 2010) and The Canadian Occupational Performance Measure (COPM; Law et al., 1990), with focus on activities that the person perceives to be associated with the sensory loss. In addition, client-selected activities of relevance to the person can be used to assess occupational performance outcomes and the impact of sensory loss on task performance (Carey, 2012). For example, the occupational task of relevance may be eating, which involves use of cutlery and cutting up food. Steps involved would include:
- Identifying occupational performance issues for the person;
- Identifying somatosensory demands of the task in relation to touch–texture, proprioception, and tactile object recognition; and
- Manipulating the sensory demands of the task to assess presence and impact of sensory loss on the task.
Please see references below for further details.
References:
Blennerhassett, J.M., Avery, R.M. & Carey, L.M. (2010). The test-retest reliability and responsiveness to change for the Hand Function Survey during stroke rehabilitation. Australian Occupational Therapy Journal, 57(6), 431-438. doi: 10.1111/j.1440-1630.2010.00884.x
Carey, L.M. (2012). SENSe: Helping stroke survivors regain a sense of touch: A manual for therapists. Melbourne, Australia: The Florey Institute of Neuroscience and Mental Health.
Carey, L.M. (2014). Core concepts in sensory impairment and recovery following stroke. In T. Wolf(Ed.), Stroke: Interventions to Support Occupational Performance (pp. 95-118). Bethesda, MD: AOTA Press.
Law M, Baptiste S, McColl M, Opzoomer A, Polatajko H, Pollock N. (1990). The Canadian occupational performance measure: An outcome measure for occupational therapy. Canadian Journal of Occupational Therapy, 57(2):82-7. doi: 10.1177/000841749005700207.
Reading: Carey, L.M. (2014). Core concepts in sensory impairment and recovery following stroke. In T. Wolf(Ed.), Stroke: Interventions to Support Occupational Performance (pp. 95-118). Bethesda, MD: AOTA Press.