Michael Leon
Professor Emeritus, Recalled, Neurobiology and Behavior
School of Biological Sciences
School of Biological Sciences
Ph.D., University of Chicago
ORCiD: 0000-0003-2684-6955
University of California, Irvine
2205 McGaugh Hall
Mail Code: 4550
Irvine, CA 92697
2205 McGaugh Hall
Mail Code: 4550
Irvine, CA 92697
Research Interests
Environmental Enrichment
Academic Distinctions
Associate dean for undergraduate education in the School of Biological Sciences.
Research Abstract
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.
This 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.
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.
This 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.
Awards and Honors
2014 D.G. Marquis Behavioral Neuroscience Award from the American Psychological Association
2011 Healthcare Technology Acceleration Award from the California HealthCare Foundation, Booz Allen Hamilton and the Robert Wood Johnson Foundation
2007 UC Irvine Professor of the Year
2007 Excellence in Teaching Award, the School of Biological Sciences
1981-1991 Research Scientist Development Award, NIMH
2011 Healthcare Technology Acceleration Award from the California HealthCare Foundation, Booz Allen Hamilton and the Robert Wood Johnson Foundation
2007 UC Irvine Professor of the Year
2007 Excellence in Teaching Award, the School of Biological Sciences
1981-1991 Research Scientist Development Award, NIMH
Short Biography
Michael Leon received his PhD from the University of Chicago and joined the professoriate at the age of 24. He is currently Professor emeritus in the Department of Neurobiology and Behavior at the University of California Irvine. He also is a member of the Center for the Neurobiology of Learning and Memory, as well as the Institute for Memory Impairments and Neurological Disorders at UCI. Dr. Leon has received multiple awards for teaching, including the Professor of the Year Award as the best teacher on the UCI campus. He has received the Research Scientist Development Award from the National Institute for Mental Health for his work on the neurobiology of early learning, the D.G. Marquis Award from the American Psychological Association for developing an effective treatment for children with autism, and the Healthcare Technology Acceleration Award from the California HealthCare Foundation for his work on body weight normalization. A recent analysis from the Stanford University ranked him among the top 2% of scientists in the world.
Publications
Cleland, T., Johnson, B.A., Leon, M., and Linster, C. Relational representation in the olfactory system. Proceedings of the National Academy of Sciences, U.S.A. 2007, 104, 1953-1958
Leon, M. and Johnson, B.A. Is there a space-time continuum in olfaction? Cellular and Molecular Life Sciences, 2009, 66, 2135-2150.
Johnson, B.A., Xu, Z., Ali, S.S., and Leon, M. Spatial representations of odorants in olfactory bulbs of rats and mice: Similarities and differences in chemotopic organization. Journal of Comparative Neurology, 2009, 514, 658-673.
Johnson, B.A., and Leon, M. Glomerular map. Encyclopedia of Neuroscience. (Binder, M.D., Hirokawa, N., and Windhorst, U., Eds.) Springer-Verlag, Berlin Heidelberg, 2009, 1745-1748.
Johnson, B.A., Ong, J., and Leon, M. Glomerular activity patterns evoked by natural odor objects in the rat olfactory bulb are related to patterns evoked by major odorant components. Journal of Comparative Neurology, 2010, 518, 1542–1555.
Johnson, B.A., Woo, C., Zeng, Y., Hingco, E.E., Ong, J., and Leon, M. Prolonged stimulus exposure reveals prolonged neurobehavioral response patterns. Journal of Comparative Neurology, 2010, 518, 1617-1629.
Aronoff, E., Hillyer, R., & Leon, M. (2016). Environmental Enrichment Therapy for Autism: Outcomes with Increased Access. Neural Plasticity, 2016, 2734915.
Woo, C.C. and Leon, M. Environmental enrichment as an effective treatment for autism: A randomized controlled trial. Behavioral Neuroscience, 2013, 127:487-97.
Woo, C.C., Donnelly, J.H., Steinberg-Epstein, R., & Leon, M. (2015). Environmental enrichment as a therapy for autism: A clinical trial replication and extension. Behavioral Neuroscience, 129, 412-422.
Leon, M. and Woo, C.C. (2018). Environmental enrichment and successful aging. Frontiers in Neurobiology and Behavior, 12, 155.
Leon M, Woo C. Environmental enrichment and successful aging. Front Behav Neurosci. 2018; 12:155.
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.
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. Effect of olfactory enrichment for older adults. JAMA Otolaryngol Head Neck Surg. 2024; 150(11):1044.
Leon M, Troscianko ET, Woo CC. Inflammation and olfactory loss are associated with at least 139 medical conditions. Front Mol Neurosci. 2024; 17:1455418.
Professional Societies
Graduate Programs
Neurobiology and Behavior
Research Centers
Center for Neurobiology of Learning and Memory
Institute for Memory Impairments and Neurological Disorders
Link to this profile
https://faculty.uci.edu/profile/?facultyId=2146
https://faculty.uci.edu/profile/?facultyId=2146
Last updated
01/11/2025
01/11/2025