Autism spectrum disorder (ASD) is expressed as a social-behavioral imbalance that often involves communication difficulties, maladaptive behaviors, cognitive dysfunction, anxiety, motor (movement) problems, seizures, and gastrointestinal distress. Commonly, individuals with ASD experience some form of atypical sensory responsiveness, including sensory over-sensitivity, sensory unresponsiveness, or sensory-seeking behaviors.

In animal models of autism, increases in both sensory stimulation and motor activity have been shown to result in many benefits, including improvements in learning and memory, reduction in aggressive behavior, decreased anxiety, and reduction of repetitive behaviors.

We have translated this approach to humans, and we have been studying the benefits of increased sensory-motor activity in children with ASD. In a clinical trial, we examined the effects of sensory-motor enrichment in children with ASD, age 3-12, and found that 42% of the children receiving the sensory- motor enrichment had a clinically significant improvement on the Childhood Autism Rating Scale (CARS). In addition, statistically significant improvements in cognition were observed in the sensory-motor enrichment group compared to the control group. Finally, 69% of parents in the sensory-motor enrichment group and 31% of parents in the control group reported improvement in their child over the 6-month study (2015).

In a second randomized clinical trial, Sensory Enrichment Therapy was again used to treat 3-6 year-old children with classic autism, Woo, Donnelly, Steinberg-Epstein & Leon (2015) again found significant improvements in the cognitive scores of enriched children using the Leiter-R, with enriched children gaining 8.42 IQ points, while the standard-care group gained 1.53 IQ points over 6 months, a statistically significant difference.  A significant improvement for the enriched children was also found in receptive language, using the Reynell Developmental Language Scales, another objective test of symptom improvement.  Enriched children gained 7.42 points on the receptive language scale, whereas the standard-care group had an average increase of 3.63 points on that assessment.

Cognitive loss in older adults is a growing issue in our society, and there is a need to develop inexpensive, simple, effective in-home treatments. Our study was conducted to explore the use of olfactory enrichment at night to improve cognitive ability in healthy older adults.

Male and female older adults (N = 43), age 60–85, were enrolled in the study and randomly assigned to an Olfactory Enriched or Control group. Individuals in the enriched group were exposed to 7 different odorants a week, one per night, for 2 h, using an odorant diffuser. Individuals in the control group had the same experience with de minimis amounts of odorant. Neuropsychological assessments and fMRI scans were administered at the beginning of the study and after 6 months.

A statistically significant 226% improvement was observed in the enriched group compared to the control group on the Rey Auditory Verbal Learning Test and improved functioning was observed in the left uncinate fasciculus, as assessed by mean diffusivity. Minimal olfactory enrichment administered at night produces improvements in both cognitive and neural functioning. Thus, olfactory enrichment provides an effective and low-effort pathway to improved brain health.

Olfactory loss accompanies at least 139 neurological, somatic, and congenital/hereditary conditions. This observation leads to the question of whether these associations are correlations or whether they are ever causal.

Temporal precedence and prospective predictive power suggest that olfactory loss is causally implicated in many medical conditions. The causal relationship between olfaction with memory dysfunction deserves particular attention because this sensory system has the only direct projection to memory centers.

Mechanisms that may underlie the connections between medical conditions and olfactory loss include inflammation as well as neuroanatomical and environmental factors, and all 139 of the medical conditions listed here are also associated with inflammation. Olfactory enrichment shows efficacy for both prevention and treatment, potentially mediated by decreasing inflammation.

Recent publications

Woo CC, Miranda B, Sathishkumar M, Dehkordi-Vakil F, Yassa MA, Leon M. Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults. Front Neurosci. 2023; 17:1200448.

Leon M, Troscianko ET, Woo CC. Inflammation and olfactory loss are associated with at least 139 medical conditions. Front Mol Neurosci. 2024; 17:1455418.

Leon M, Woo CC. Olfactory loss is a predisposing factor for depression, while olfactory enrichment is an effective treatment for depression. Front Neurosci. 2022; 16:1013363.

Leon M, Woo C. Environmental enrichment and successful aging. Front Behav Neurosci. 2018; 12:155.

Leon M. Effect of olfactory enrichment for older adults. JAMA Otolaryngol Head Neck Surg. 2024; 150(11):1044.

Aronoff E, Hillyer R, Leon M. Environmental enrichment therapy for autism: outcomes with increased access. Neural Plast. 2016;2016:2734915.

Woo CC, Donnelly JH, Steinberg-Epstein R, Leon M. Environmental enrichment as a therapy for autism: A clinical trial replication and extension. Behav Neurosci. 2015; Aug;129(4):412-22.

Woo CC, Leon M. Environmental enrichment as an effective treatment for autism: a randomized controlled trial. Behav Neurosci. 2013; 127(4):487-97.