By Anna Tarasova ’19
Hypersensitivity to sensory stimuli is frequently an aspect of autism spectrum disorders (ASD), and can lead to defensiveness against touch and other sensory stimuli. This can contribute to hyperactivity and lead to inattention, learning difficulties, sleep disturbances, anxiety, and many other symptoms of autism. Although the mechanism of this phenomenon has long been unknown, Dr. Cynthia He and her colleagues at UCLA have found that it may be caused by the inability of neurons in the somatosensory cortex of the brain to adapt to repetitive stimulation.
Dr. He explored the phenomenon of tactile defensiveness using a model of 14-16-day-old Fmr1 knockout (KO) mice. Fmr1 KO is commonly associated with Fragile X Syndrome (FXS), an ASD. Young mice specifically were used because FXS presents in humans within their first year of life. The mice were determined to be hypersensitive to whisker stimulation, presenting with an exaggerated response. Three potential hypotheses for the hypersensitivity were tested: somatosensory neurons fire more frequently than normal in this type of mice, a higher proportion of neurons respond to stimulation, and neurons have decreased adaptation to repetitive sensory stimuli. The third hypothesis was found to be the most plausible. In normal mice, neuronal response to a later set of whisker stimulations was lowered compared to neuronal response to an initial set. However, in Fmr1 KO mice, neuronal response did not decrease between the two sets. This result persisted in an adult mouse group. However, the adult mice avoided the stimulus rather than affecting an exaggerated response like the young mice.
Knowing the mechanisms involved in autism-associated hypersensitivity could help researchers develop a treatment that would affect multiple aspects of the disorder, since this symptom is involved in modulating attention, learning difficulties, depression, and many other parts of ASD.
- C. He et al., Tactile defensiveness and impaired adaptation of neuronal activity in the Fmr1 knockout mouse model of autism. The Journal of Neuroscience, 2017. doi: 10.1523/JNEUROSCI.0651-17.2017