Introduction 

Ferguson explains that up to 91% of autistic people experience GI difficulties, highlighting the importance of studying GI issues in relation to autism (2:40). Two of the most common GI issues in autism are constipation and irritable bowel syndrome (3:50). Ferguson asserts that altered autonomic nervous system response to stress in autism is linked to these conditions. The speaker outlines the autonomic nervous system (ANS), which controls smooth muscles like those used in breathing and digestion. The ANS is composed of the parasympathetic (PYM) (i.e., rest and digest) and the sympathetic (SYM) (i.e., fight, flight, freeze) branches. Ferguson explains that our bodies strive for a balance between these two systems (7:16). He emphasizes that intestine function is inhibited when the SYM is activated and posits that this could be why individuals with high-stress responses are often constipated (6:40). Ferguson presents numerous studies supporting the assertion that ANS imbalances are associated with GI and behavior difficulties in autism.  

Study 1: GI and stress relationship in autism 

This study correlated stress response scores with GI issues in autistic children and adolescents. Baseline cortisol (stress hormone) levels were compared to levels after participants dipped their hands in cold water. They correlated this stress response to GI problems and found that Lower GI issues (e.g., abdominal pain and constipation) positively correlated with cortisol levels (8:12). The study also found a positive correlation between Upper GI issues and inflammation (10:00). Ferguson states that these results suggest that autistic individuals with lower GI issues will likely have high cortisol response to stressors (9:40).  

Study 2: Psychophysiological associations 

The presenter explains that heart rate variability (HRV) measures the balance between the PYM and SYM. This study correlated HRV scores with Lower GI issues in autistic children and adolescents. Findings showed HRV response to stressors is much higher than average in autistic individuals who have anxiety. The same relationship exists between regressive autism and HRV (12:00). Ferguson therefore asserts that co-occurring anxiety disorders or regressions in autism alter the relationship between the PYM and the GI tract. This transformed relationship, he continues, is likely the cause of many GI issues in autism (13:05).  

Study 3: GI problems, problem behavior, and internalizing symptoms in autism 

This study aimed to look at the relationship between GI problems, problem behaviors, and internalizing symptoms (e.g., anxiety) in autism. The speaker outlines study methods (14:11) and explains how they correlated scores across two age groups (15:43). Results showed that overall, younger children (ages 2 – 5) have more dietary problems than the older group (ages 6 – 18). However, for both groups, the following data was presented (16:30): 

• 65% experienced constipation 

• 50% experienced stomach aches or pain 

• 29% experienced diarrhea 

• 23% experienced nausea 

• 93% were not taking GI medication 

• 53% were taking medications for other reasons (ADHD, aggression) 

The study also assessed whether or not GI symptoms predict internalizing or externalizing symptoms (i.e., anxiety or problem behaviors) (18:44). Researchers found that the younger children acted out more with aggression while the older group had more internalized symptoms. This relationship, he continues, is compounded when an individual is minimally or non-verbal (20:20). Ferguson therefore asserts that GI issues must be addressed in this population, especially in those with communication difficulties (21:44).  

Study 4: Electrodermal activity and problem behaviors in autism  

Electrodermal activity, or sweating, is an indicator of stress. This study aimed to see if sweating predicts problem behaviors (22:45). Participants wore sweat monitors, and researchers observed their behaviors in an educational setting (26:00). Results showed (27:10) that there is a rise in skin conductance lasting an average of about 10 minutes leading up to problem behaviors (29:45). This change in conductance is called the anticipatory rise, and it occurred before problem behaviors in 60% of observations (28:30). Ferguson posits that this anticipatory rise is likely the result of discomfort or pain and that it presents an opportunity for caretakers to intervene in the stress response. He outlines two clinical trials using propranolol to treat anxiety (31:15) and constipation (35:10). 

Study 5: Effects of propranolol on the relationship between GI issues and amygdalar reactivity 

The amygdala is a part of the central nervous system responsible for ANS activation. This study examined the effect of three medications on amygdalar response to emotional faces using fMRI technology (36:20). Participants took three 12-day sessions of different medications: placebo, nadolol, and propranolol. Propranolol is the only one known to penetrate the blood-brain barrier. At the end of each session, participants completed a face-matching task to activate the amygdala (39:00). Researchers correlated GI issues to fMRI results. They found that with the first two medications (placebo and nadolol), there was a statistically significant positive relationship between GI symptoms and amygdalar activity. Contrastingly, after 12 days of propranolol, there was no relationship between GI symptoms and amygdalar activity (40:14). Therefore, Ferguson posits that GI stress is related to the central nervous system. He notes the limitations of this study (42:10).  

What’s next? 

The presenter describes Transcutaneous Vagus Nerve Stimulation (tVNS) and its potential in treating atypical PYM activation and GI issues in autism. tVNS is a small device that fits in the ear and stimulates the vagus nerve, which is part of the PYM (rest and digest) system. This stimulation helps the body calm down (43:00). Ferguson underscores the difference between blocking SYM activity (i.e., propranolol) and stimulating the PYM (tVNS). He summarizes the presentation and reiterates that GI issues in autism are often associated with an enhanced stress response. This is particularly true for Lower GI issues like constipation. GI symptoms, he continues, have also been associated with internalizing symptoms (i.e., anxiety) and problem behaviors. Stress response activation may often proceed problem behaviors in autism, and much more research is needed on new treatment strategies. Ferguson provides thanks and acknowledgments before the Q&A.