A quarterly publication of the Autism Research Institute

The Autism Research Review International is quarterly publication of the Autism Research Institute

Fall, 2016 | Number 4, Volume 30

Editorial – Internal sensory stress and discomfort or pain

by Stephen M. Edelson, Ph.D.

Many individuals on the autism spectrum suffer from recurring or chronic discomfort or pain. On occasion, parents and physicians suspect that someone may be suffering from a medical problem, but it can be very difficult to pinpoint the source. As a result, physicians may order laboratory testing, x-rays, and in extreme cases, exploratory surgery. 

It is often assumed that these people have difficulty communicating their discomfort or pain verbally or physically (e.g., touching, pointing). However, research on sensory issues, along with reports from adults with autism and their parents, suggests that the lack of expression of discomfort or pain could be a result of diminished or dulled internal sensations. Alternately, internal discomfort or pain may be perceived as being more intense than it is by neurotypical individuals with the same underlying medical problems. 

Types of Sensory Processing 

Dr. Lucy J. Miller, a pioneering researcher in sensory processing, and her colleagues have demonstrated that those on the spectrum respond to sensory stimulation in distinct ways. Using a standardized procedure to evaluate sensory processing called the Sensory Challenge Protocol, Miller and her colleagues measured sympathetic neural activity associated with various types of external stimulation. Their findings revealed that many on the spectrum were hyposensitive and had a diminished response to sensory sensations. In contrast, others were hypersensitive, exhibiting an enhanced reaction to the same sensory stimuli. 

Interoception is a relatively new area of interest among those in the sensory processing field. It refers to the perception of sensory-related stimulation within the body and includes feelings of pain, muscle tension, bladder tension, hunger, and much more. In her new book, Interoception: The Eighth Sensory System, Kelly Mahler, M.S., OTR/L, reviews a range of research surrounding interoception and links this research to the common experiences of people with autism. Mahler describes three types of difficulty with interoceptive awareness: 

Interoceptive underresponsivity. This refers to hyposensitivity or diminished sensations. Thus, these individuals may feel little or no discomfort or pain while suffering from a medical condition. Consistent with this description, a study by Fiene and Brownlow (2015) involving 74 adults with autism and 228 controls found that those on the spectrum had much lower levels of “sensing internal bodily states.” At the Autism Research Institute, we have heard reports of people who did not show outward signs of discomfort or pain while suffering from issues such as a ruptured appendix, impacted stools in the gastrointestinal tract, or a severe ear infection. 

Interoceptive responsivity. This refers to hypersensitivity or over-responsiveness; thus, internal sensations may actually be enhanced. Dr. Micah Mazurek and her colleagues found that children on the spectrum were over-responsive as well as anxious as a result of pain-associated gastrointestinal problems. Furthermore, Dr. Edward Carr and his colleagues found that behavioral challenges in the classroom occurred more often on “sick” days as well as days of menstrual discomfort. The behaviors noted included property destruction, meltdowns, aggression, stereotypies, and self-injurious behavior. 

Interoceptive discrimination difficulty. A third type of interoception, termed “discrimination difficulty,” refers to an individual who has a “vague” or “general” feeling of an internal sensation but cannot provide details of this feeling. An example would be someone who feels anxious but is unable to determine that this anxiety is a result of some form of discomfort or pain. 

Possible Reasons for Difficulties in Interoception 

Research in several areas, including neurology, metabolism, biochemistry, and even nutrition, may shed light on interoceptive challenges. Focuses of investigation include: 

Interoception is a relatively new area of interest among those in the sensory processing field. Interoception refers to the perception of sensory-related stimulation within the body and includes feelings of pain, muscle tension, bladder tension, hunger, and much more.

Insula. The insula is located deep within the cerebral cortex, within the lateral sulcus. The lateral sulcus separates the temporal and parietal lobes and is known to be responsible for internal sensations, emotional regulation, and autonomic nervous system control. Research on the insula in autism has documented hypo-connectivity in some individuals, and hyper-connectivity in others. In addition, one study found reduced gray matter in the insula of those with autism. 

Minicolumns. Research conducted by Dr. Manuel Casanova and others has documented impaired minicolumns in the neocortex, including sensory regions, in people with autism. Dr. Casanova has suggested different reasons for hypersensitivity and hyposensitivity. Basically, the threshold of reactivity to a sensory stimulus is lower in those with autism. Thus, a relatively weak stimulus would cause more neural fi ring (i.e., action potential) and lead to increased sensitivity or hyper-reactivity. However, hyposensitivity would occur as a result of additional neural fi ring (i.e., noise) due to stimulation from adjacent neurons or minicolumns. This would make the stimulus in question less distinguishable and lead to reduced sensitivity or hypo-reactivity (i.e., low signal-to-noise ratio). 

Metabolism. There has been much discussion yet little research on the possible connection between mitochondrial impairment and sensory dysfunction. A recent study by Dr. Richard Frye and his colleagues found that a unique form of mitochondrial impairment was related to the occurrence of severe repetitive behaviors. Repetitive behaviors have often been assumed to provide self-stimulation to a hyposensitive sensory system. They may also serve the opposite purpose, reducing sensory input by redirecting one’s attention away from the source of discomfort or pain. ARI is collaborating with Drs. Frye and Miller to further understand the possible relationship between mitochondrial impairment and sensory processing. 

Biochemistry. The endorphin theory of autism, originally proposed by Dr. Jaak Panksepp, proposes that endorphins, which are endogenous opiate-like substances, may lead to diminished sensations within the body. As a way to handle severe pain, the body releases endorphins during behaviors such as self-injury, which in turn dampen the pain and lead to pleasurable feelings. Another possibility, proposed by many practitioners and researchers, is a partial breakdown of casein and gluten proteins in an inflamed and “leaky” gut that allows these proteins to seep into the bloodstream. These endorphin-like peptides, casomorphin and gluteomorphin, then circulate throughout the body, leading to a dulling of sensory sensations as well as feelings of pleasure. 

Nutrition. Certain deficiencies may lead to sensory hypersensitivity. For example, sound sensitivity may be a result of a magnesium deficiency; bone pain may be caused by a vitamin D deficiency; and itchy eyes (which may lead to eye pressing or poking) may be a result of a calcium deficiency. 

ARI’s Upcoming Study on Interoception 

The Autism Research Institute is currently orchestrating a multidisciplinary study to develop communication strategies that will allow individuals on the spectrum to indicate areas of discomfort and pain. Experts in sensory processing will provide input regarding various means of expression (or lack of expression); behavioral experts in functional communication will help figure out ways to teach individuals how to express themselves; and physicians will provide input regarding the types of medical conditions associated with interoceptive problems. 

We hope that by working collaboratively, we can increase awareness of the sensory and medical issues often associated with autism as well as develop a common language to better communicate within the sensory, medical, and behavioral fields. By understanding how those on the autism spectrum react (or fail to react) to a medical condition typically associated with discomfort or pain, physicians will be better able to diagnose and treat these individuals.