Children with developmental disabilities, like cerebral palsy, may have a dysfunctional sensory system. This means that one or more of their senses are either over- reactive or under- reactive to stimuli. These sensory problems may be the underlying reason for such behaviors as rocking, spinning, and hand-flapping. Although the receptors for the senses are located in the peripheral nervous system, it is believed that the problem derives from a neurological dysfunction in the central nervous system (the brain).
Sensory integration is an innate neurobiological process and refers to the integration and interpretation of the sensory stimuli from the environment by the brain. Sensory integrative dysfunction is a disorder in which sensory input is not integrated or organized appropriately in the brain and may produce varying degrees of problems in development, information processing, and behavior. A general theory of sensory integration and treatment has been developed from studies in the neurosciences and those pertaining to physical development and neuromuscular function.
Sensory integration focuses primarily on three basic senses: tactile, vestibular, and proprioception. Their interconnections start forming before birth and continue to develop as the person matures and interacts with the environment. The three senses are not only interconnected but are also connected with other systems in the central nervous system. Although these three sensory systems are less familiar than vision and audition, they are critical to our basic survival. The interconnection between these three senses is complex. Basically, they allow us to experience, interpret, and respond to different stimuli in our environment.
The tactile system provides us with information about touch sensations such as pressure, vibration, movement, temperature and pain. We get tactile information through sensory receptors located in the skin. These play an important role in perceiving the environment as well as protective reactions for survival. Dysfunction in the tactile system can be seen in withdrawing when being touched, refusing to eat certain foods or to wear certain types of clothing, complaining about having one’s hair or face washed, avoiding getting one’s hands dirty (i.e., glue, sand, mud, finger-paint), and using one’s finger tips rather than whole hands to manipulate objects. A dysfunctional tactile system may lead to a misperception of touch or pain (hyper- or hyposensitive) and may lead to self-imposed isolation, general irritability, distractibility, and hyperactivity. Tactile defensiveness is a condition in which an individual is extremely sensitive to light touch.
Theoretically, when the tactile system is immature and working improperly, abnormal neural signals are sent to the cortex in the brain which can interfere with other brain processes. This, in turn, causes the brain to be overly stimulated and may lead to excessive brain activity, which can neither be turned off nor organized. This type of over-stimulation in the brain can make it difficult for an individual to organize one’s behavior and concentrate and may lead to a negative emotional response to touch sensations.
The vestibular system refers to structures within the inner ear (the semi-circular canals) that detect movement and changes in the position of the head. For example, the vestibular system tells you when your head is upright or tilted (even with your eyes closed). Dysfunction within this system may manifest itself in two different ways. Some children may be hypersensitive to vestibular stimulation and have fearful reactions to ordinary movement activities (e.g., swings, slides, ramps, inclines). They may also have trouble learning to climb or descend stairs or hills; and they may be apprehensive walking or crawling on uneven or unstable surfaces. As a result, they seem fearful in space. In general, these children appear clumsy.
On the other extreme, the child may actively seek very intense sensory experiences such as excessive body whirling, jumping, and/or spinning. This type of child demonstrates signs of a hypo-reactive vestibular system; that is, they are trying continuously to stimulate their vestibular systems.
Proprioception is the sensation of joint motion and acceleration, it the sensory feedback mechanism for motor control and posture. When proprioception is functioning efficiently, an individual’s body position is automatically adjusted in different situations; for example, the proprioceptive system is responsible for providing the body with the necessary signals to allow us to sit properly in a chair and to step off a curb smoothly. It also allows us to manipulate objects using fine motor movements, such as writing with a pencil, using a spoon to drink soup, and buttoning one’s shirt. Some common signs of proprioceptive dysfunction are clumsiness, a tendency to fall, a lack of awareness of body position in space, odd body posturing, minimal crawling when young, difficulty manipulating small objects (buttons, snaps), eating in a sloppy manner, and resistance to new motor movement activities.
Another dimension of proprioception is praxis or motor planning. This is the ability to plan and execute different motor tasks. In order for this system to work properly, it must rely on obtaining accurate information from the sensory systems and then organizing and interpreting this information efficiently and effectively.
Any dysfunction in these three systems can lead to many unwanted effects. A child may be over- or under-responsive to sensory input, activity level may be either unusually high or unusually low, and a child may be in constant motion or total apathy. Gross or fine motor coordination problems are also common when these three systems have this dysfunction. Easy distraction of attention, impulsive and aggressive behaviors are often in many children.
Evaluation and treatment of basic sensory integrative processes is performed by occupational therapists or physical therapists. The therapist’s general goals are:
1) to provide the child with sensory information which helps organize the central nervous system,
2) to assist the child in modulating sensory information,
3) to assist the child in processing a more organized response to sensory stimuli.