Kolodny, T. | bioRxiv Science

bioRxiv2018

Disrupted neural adaptation in autism spectrum disorder

There has been long-standing speculation that autism spectrum disorder (ASD) involves an increase in excitation relative to inhibition. However, there is little direct evidence of increased neural excitation in humans with ASD. Here we provide a potential explanation for this discrepancy: we show that increased neural excitation emerges only after repeated stimulation, manifesting as a deficit in neural adaptation. We measured fMRI responses induced by repeated audio-visual stimulation and button presses in early sensory-motor cortical areas. Across all cortical areas we show reduced adaptation in individuals with ASD compared to neurotypical individuals. The degree of adaptation is correlated between cortical areas and with button-press reaction times across subjects. These findings suggest that increased neural excitation in ASD, manifesting as dysregulated neural adaptation, is domain-general and behaviorally-relevant.

neuroscience↗

bioRxiv2018

Glutamatergic facilitation of neural responses in MT enhances motion perception in humans

There is large individual variability in human neural responses and perceptual abilities. The factors that give rise to these individual differences, however, remain largely unknown. To examine these factors, we separately measured fMRI responses to moving gratings in the motion-selective region MT, and perceptual duration thresholds for motion direction discrimination within the same group of male and female subjects. Further, we acquired MR spectroscopy data that allowed us to quantify an index of neurotransmitter levels in the region surrounding MT. We show that individual differences in the Glx (glutamate + glutamine) signal in the MT region are associated with both higher fMRI responses and improved psychophysical task performance. Our results suggest that individual differences in baseline levels of glutamate within MT contribute to motion perception by increasing neural responses in this region.\n\nSignificanceWhat factors govern the relationship between neural activity and behavior? Our results suggest that one such factor is the level of glutamate, an excitatory neurotransmitter, within a particular region of cortex. By measuring an index of glutamate in vivo using magnetic resonance spectroscopy, we show that human subjects with more glutamate in the visual motion area known as MT also have larger fMRI responses (an index of neural activity) in this region. Further, people with more glutamate in MT can accurately perceive moving images presented more briefly within a behavioral task. Our findings point to an important role for glutamate levels in determining the relationship between neural responses and behavior during visual motion perception.

neuroscience↗