Sensory stimulation therapy

By 2025, it is estimated that 34 million people in the United States will have dementia. It is extremely important, then, that we establish an effective treatment for people with such symptoms to either reduce, or diminish dementia altogether. In modern-day treatment not involving pharmacological treatment, psychosocial therapies are a great intervention. With psychosocial therapies such as massage, aromatherapy, multi-sensory stimulation, music therapy, and reality orientation, treatment of dementia and dementia related diseases has become possible in a less traditional yet non-pharmacological form.[1] It was once believed that the brain was largely unchanging and that its function was decided at a young age.[2] Along this train of thought, cognitive loss from strokes and ageing were viewed as unrecoverable. Functional Localization is a theory which suggests that each section of the brain has a specific function, and that loss of a section equates to permanent loss of function. Traditional models even specialize between hemispheres of the brain and describe "artistic and logical sections of the brain." This fatalistic outlook has been dramatically challenged by the recent paradigm of Brain Plasticity.

Brain plasticity refers to the ability of the brain to restructure itself, form new connections, or adjust the strength of existing connections.[3] The current paradigm allow for conceptualization of brain that is capable of change. Various researchers are using this concept to develop new therapies for conditions that were previously viewed as permanent; for example Paul Bach-y-Rita has worked on devices to give sight to blind individuals, and alleviate a feeling of falling in a patient that has lost function of the vestibular apparatus.

It has been found that many senses have some plastic nature about them. Even auditory cognition has been shown to have some potential for recovery after stroke. A recent study by Sarkamo et al. has shown that listening to music and audio books during early recovery from stroke can result in improved cognition.[4]

This paradigm has opened doors into the previously believed to be impossible; recovery from strokes, reduced cognitive ageing.

CT scan slice of the brain showing a right-hemispheric ischemic stroke (left side of image).

A stroke can be caused by a few different situations, but the basic result is the same. Blood flow to a section of the brain is stopped, which results in rapid depletion of oxygen and other nutrients in the starved section. The starved section of brain tissue quickly begins to die, and results in a lesion in the brain. The resulting lesion can be traced loss of various cognitive functions depending on the location and area of damage.[5]

It is common for stroke patients to suffer from muscle weakness and loss of muscle function. Some natural recovery has been observed, however training based in advances in neuroscience have shown the most dramatic improvements. These investigational therapies focus on repetition of basic tasks with limited appendages. It is generally found that more intensive remedial function therapies result in the greater restoration to function.[6] fMRI and PET scan studies have shown that after as little as 3 weeks of the intensive training programs there are statistical differences between the experimental group and controls, with observable improvements in muscle control.[7] Although these methods have opened doors for improved quality of life for stroke patients, the training methods are very time, and attention intensive. It would be a powerful tool if one could find a system that does not have massive attention requirements.

During ageing many brain functions decline and some are lost, this is referred to as cognitive aging. In the most extreme cases one might think about the catastrophic results of Alzheimer's Disease. Age is the largest risk factor for Alzheimer's disease. However, due to lack of knowledge and successful research in this field, little is known about the rates of clinical decline and brain atrophy.[1] This disease is associated with neuronal death. However more general ageing considers loss of synaptic strength over neuronal death.[8] When considering this situation the machinery for proper functioning of the brain is still present, but is in disarray. It has been shown that as much as a 46% decrease in dendrite spine number and density can occur in humans over 50 years old when compared to older participants.[9]

The cortical homunculus, or the visual representation of how your brain sees your body, was discovered by Wilder Penfield

The cortical homunculus, or the visual representation of how your brain sees your body, was discovered by Wilder Penfield. a world-famous brain surgeon. Upon ending his career as part of the McGill medical faculty, he served as the director of Neurological Institute.

The Somatosensory systemis the part of our sensory system that deals with touch. We wouldn't be able to feel things like temperatures, pain, pressure, vibration, and skin rash without the unwavering help of our somatosensory system.[10] The peripheral nervous system has the ability to understand touch, pressure, vibration, limb position, heat, Cold, and Pain. This information is sent through the peripheral nervous system, to the spinal cord where it is finally processed by the brain. One of the key structures in processing this information is the primary somatosensory cortex, which is located in the parietal lobe. The primary somatosensory cortex is known to have subsections that process information from different sections, and the area of the cortex for each section is related to its acuity. This observation is often shown symbolically through a Homunculus.[11]

Sensory Stimulation utilizes rapid stimulation of nerves in a section of skin to drive neuronal changes in the participant. The nerves are electrically stimulated in a fashion referred to as coactivation.[12][13] In both cases the participant's limb, often hand, is constrained in a device that has a section that applies the stimulation. The participant is allowed to go about their daily activities, and many do not mind the presence of the device.[12] These degree of reorganization is often measured through two point discrimination thresholds, which measure the smallest distance between two points that can be felt by the subject.

It has been shown that the use of this technique can rest as much as 30 years of sensory loss.[12] In the study by Dinse et al., 28 patients between the ages of 66 to 86 tested similarly to participants 30 years younger than themselves after treatment. These participants had the device attached for 3 hours while undergoing stimulation. Other studies have used shorter periods of stimulation and achieved similar results.[14]

Sensory Stimulation Therapy is a developing technique aimed at recovering sensory loss after strokes and restoring losses from ageing. It has not been proven that sensory stimulation therapy can actually improve brain plasticity, nor cognitive function. The paradigm of brain plasticity marked a fundamental change in the way that the brain is understood, and considered for future therapies.[2] SS takes advantage of this paradigm and the senses are presented with simple stimulation to cause changes inside the brain. In this particular situation a section of skin is stimulated either through electrical or physical means. Signals are sent through the peripheral nervous system to the somatosensory cortex.[12][13] These signals are then the impetus for changes inside the brain. It has been shown that the adjustment of frequency in this technique can be used to induce either Long Term Potentiation or Long Term Depression.[15] In the case of LTP as much as 30 years of sensory loss has been shown to be recoverable in relatively short time periods.[12] SS has been paired with Use Dependant Plasticity training systems and it has been shown that enhanced recovery is produced from the combination.[14] One of the striking advantages of this technique is that it is not necessary for the participant to pay attention to the stimulus in order to gain benefit from the therapy.[12] This technique opens many interesting doors for future therapies. A potential challenge for this technique is that there is little transfer of gains from one section of skin to another.

Many studies have been conducted, most with some kind of positive conclusion however, further studies need to be conducted sensory stimulation in dementia in order to prove or disprove any theories.[19]

• Multisensory integration
• Sensory processing disorder
• Sensory integration therapy