Biology subjects

Murray, S. O.

Publications and source records attributed to Murray, S. O..

4 recordsLinked to original sources

bioRxiv2023

Cortical Surface Area Relates to Distinct Computational Properties in Human Visual Perception

Understanding the relationship between cortical structure and function is essential for elucidating the neural basis of human behavior. However, the impact of cortical structural features on the computational properties of neural circuits remains poorly understood. In this study, we demonstrate that a simple structural feature - cortical surface area (SA) - relates to specific computational properties underlying human visual perception. By combining psychophysical, neuroimaging, and computational modeling approaches, we show that differences in SA in the parietal and frontal cortices are associated with distinct patterns of behavior in a motion perception task. These behavioral differences can be accounted for by specific parameters of a divisive normalization model, suggesting that SA in these regions contributes uniquely to the spatial organization of cortical circuitry. Our findings provide novel evidence linking cortical structure to distinct computational properties and offer a framework for understanding how cortical architecture can impact human behavior.

neuroscience↗

bioRxiv2019

Weaker neural suppression in autism

Increased neural excitation resulting from weakened inhibition is a leading hypothesis for the pathophysiology of autism. However, experimental support in humans remains equivocal. Alternatively, modulatory processes that suppress neural responses but do not specifically rely on inhibition may be impacted in ASD. Leveraging well-characterized suppressive neural circuits in the visual system, we used behavioral and fMRI tasks to demonstrate a significant reduction in neural suppression in young adults with ASD compared to neurotypical controls. We further tested the mechanism of this suppression by measuring levels of the inhibitory neurotransmitter GABA, and found no differences in GABA between groups. We show how a computational model that incorporates divisive normalization, as well as narrower top-down gain (that could result, for example, from a narrower window of attention), can explain our observations and divergent previous findings. Thus, weaker neural suppression in ASD may be attributable to differences in top-down processing, but not to differences in GABA levels.

neuroscience↗

bioRxiv2018

The time course of different surround suppression mechanisms

What we see depends on the spatial context in which it appears. Previous work has linked the reduction of perceived stimulus contrast in the presence of surrounding stimuli to the suppression of neural responses in early visual cortex. It has also been suggested that this surround suppression depends on at least two separable neural mechanisms, one low-level and one higher-level, which can be differentiated by their response characteristics. In a recent study, we found evidence consistent with these two suppression mechanisms using psychophysical measurements of perceived contrast. Here, we used EEG to demonstrate for the first time that neural responses in the human occipital lobe also show evidence of two separable suppression mechanisms. Eighteen adults (10 female and 8 male) each participated in a total of 3 experimental sessions, in which they viewed visual stimuli through a mirror stereoscope. The first session was used to definitively identify the C1 component, while the second and third comprised the main experiment. ERPs were measured in response to center gratings either with no surround, or with surrounding gratings oriented parallel or orthogonal, and presented either in the same eye (monoptic) or opposite eye (dichoptic). We found that the earliest ERP component (C1; [~]60 ms) was suppressed in the presence of surrounding stimuli, but that this suppression did not depend on surround configuration, suggesting a low-level suppression mechanism which is not tuned for relative orientation. A later response component (N1; [~]160 ms) showed stronger surround suppression for parallel and monoptic stimulus configurations, consistent with our earlier psychophysical results and a higher-level, binocular, orientation-tuned suppression mechanism. We conclude that these two surround suppression mechanisms have distinct response time courses in the human visual system, which can be differentiated using electrophysiology.

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↗