Internal sensory stress and discomfort/pain in autism

The following is an editorial written by my good friend Steve Edelson ( It recently appeared published in Autism Research Review International (Volume 30, Number 4), a quarterly publication of the Autism Research Institute.  Steve gave me permission to reblog the same.

Abnormalities in sensory perception are now recognized as contributors to diagnosis in autism spectrum disorder. In those individuals capable of communicating it may be a reason why they may not be able to fully disclose internal discomfort. As an example,  the pain of a gastritis may be manifested by  head banging, thus leaving the physician to guess as to any possible underlying pathology.

The reason(s) for misinterpretation of sensory perception are not known. In his editorial, Steve mentions several possible explanations from the literature, some of which are mine.  At present we are pursing 2 main avenues to identify any possible  underlying mechanisms. First we are interested in autonomic dysregulation in autism. The autonomic system is that part of the central nervous system that regulates body functions for which we have no conscious control, e.g., heart rate. Many individuals with autism display marked dysfunction of the autonomic system. This alteration may well alter the way we perceive how our body reacts to the environment. Second, our research has also shown that the nervous system of individuals with autism is assembled differently from neurotypicals. In autism, modules of the brain called minicolumns are structures so that they are not properly functionally separated from their neighbors.  This decreases contrast while exaggerating some noise signals.

EDITORIAL: Stephen M. Edelson, Ph.D.
Internal sensory stress and discomfort/pain

Many individuals on the autism spectrum suffer from recurring or chronic discomfort and/or pain. On occasion, parents and physicians suspect that an individual may be suffering from a medical problem, but pinpointing the source of pain is difficult. As a result, physicians may order laboratory testing, x-rays, and in extreme cases, exploratory surgery.

It is often assumed these individuals have difficulty verbally articulating or physically pointing to or touching the location of their discomfort or pain. However, research on sensory issues, along with reports from adults with autism and their parents, suggests that their lack of expression of discomfort or pain could be a result of diminished or dulled internal sensations rather than a cognitive issue of not understanding the task of identifying the location of the pain. For some people with autism, internal discomfort may feel more intense for the same underlying medical problems than it does in neurotypical individuals.

Types of Sensory Processing

Dr. Lucy J. Miller, a pioneering researcher in sensory processing, and her colleagues have demonstrated that those on the autism spectrum respond to sensory stimulation in distinct ways. Using a standardized physiologic 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 of those on the autism spectrum were under sensitive and had a diminished response to sensation. In contrast, others were hyper-sensitive and exhibited an enhanced reaction to the same sensory stimuli.

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 organs of the body and includes feelings of pain, muscle tension, bladder tension, hunger, and much more. In her new book titled Interoception: The Eight 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 interoceptive awareness:

Interoceptive underresponsivity.  Similar to Miller’s findings, “interoceptive underresponsivity” 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 on the autism spectrum 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 those on the spectrum who did not show outward signs of discomfort or pain while suffering from a ruptured appendix, impacted stools in the gastrointestinal tract, or a severe ear infection.

Interoceptive responsivity.  Consistent with Miller’s findings, “interoceptive responsivity” refers to hypersensitivity or over-responsiveness; thus, internal sensations may actually be enhanced.  Dr. Micah Mazurek and her colleagues found that children on the autism 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 locate (discriminate) details of this feeling. An example would be someone who feels anxious but is unable to decipher what sensations might be related to this anxiety.

Possible Reasons for Difficulties in Interoception

Research in several areas, including neurology, metabolism, biochemistry, occupational therapy (sensory-based) and even nutrition, may shed light on interoceptive challenges. Focuses of investigation include:

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 other individuals. 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 individuals with autism. Dr. Casanova has suggested different reasons for hypersensitivity and hyposensitivity in these individuals. Basically, the threshold of reactivity to a sensory stimulus is lower in those with autism. Thus, a relatively weak stimulus would cause more neural firing (i.e., action potential) and lead to increased sensitivity or hyper-reactivity. However, hyposensitivity would occur as a result of additional neural firing (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 associated with providing 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 dampens the pain and leads to pleasurable feelings (from the endorphins). Another possibility, proposed by many practitioners and researchers, is a partial breakdown of casein and gluten proteins in an inflamed and “leaky” gut, which in turn 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 such as developing figures that show organs which can be  pointed to showing “what hurts;” 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 individuals on the autism spectrum react (or fail to react) to a medical condition typically associated discomfort or pain, physicians will better to able to diagnose and treat these individuals.

2 responses to “Internal sensory stress and discomfort/pain in autism

  1. Decades of multidisciplinary research indicated a four sending neuron axon initial segment space-time event action potential velocity manifold, with simple illustrated math, likely explaining bipolar disorder pathologies. (Newton, JR, Med. Hypotheses 1999,vol 52) This is currently strongly supported by multiple significant gene-imaging studies, e.g., (Thompson et al., 2014 reviewed common variants and structures.) This simplest nerve net manifold likely explains current abnormal sensory-motor timing factors, and dynamic spectrums of neuropsychiatric manifold dyscoordination, including autisms.


  2. Interesting blog. One current line of research in my lab is looking at endogenous opioid/endorphin molecules in an animal model of self injurious behavior. We are examining specific brain regions (as opposed to the previous CSF based studies) and have some interesting patterns of altered expression for both ligands and receptors in multiple brain regions (we are currently writing this up, so I will refrain from details).

    Liked by 1 person

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