Responses to interocular disparity correlation in the human cerebral cortex

Purpose: Perceiving binocular depth relies on the ability of our visual system to precisely match corresponding features in the left and right eyes. Yet how the human brain extracts interocular disparity correlation is poorly understood. Methods: We used functional magnetic resonance imaging (fMRI) to characterize brain regions involved in processing interocular disparity correlation. By varying the amount of interocular correlation of a disparity-defined random-dot-stereogram, we concomitantly controlled the perception of binocular depth and measured the percent Blood-Oxygenation-Level-Dependent (%BOLD)-signal in multiple regions-of-interest in the human occipital cortex and along the intraparietal sulcus. Results: A linear support vector machine classification analysis applied to cortical responses showed patterns of activation that represented different disparity correlation levels within regions-of-interest in the visual cortex. These also revealed a positive trend between the difference in disparity correlation and classification accuracy in V1, V3 and lateral occipital cortex. Classifier performance was significantly related to behavioural performance in dorsal visual area V3. Cortical responses to random-dot-stereogram stimuli were greater in the right compared to the left hemisphere. Conclusions: Our results show that multiple regions in the cerebral cortex are sensitive to changes in interocular disparity correlation, and that dorsal area V3 may play an important role in the early transformation of binocular disparity to depth perception

GABA and glutamate in hMT+ link to individual differences in residual visual function after occipital stroke

BACKGROUND: Damage to the primary visual cortex following an occipital stroke causes loss of conscious vision in the contralateral hemifield. Yet, some patients retain the ability to detect moving visual stimuli within their blind field. The present study asked whether such individual differences in blind field perception following loss of primary visual cortex could be explained by the concentration of neurotransmitters γ-aminobutyric acid (GABA) and glutamate or activity of the visual motion processing, human middle temporal complex (hMT+). METHODS: We used magnetic resonance imaging in 19 patients with chronic occipital stroke to measure the concentration of neurotransmitters GABA and glutamate (proton magnetic resonance spectroscopy) and functional activity in hMT+ (functional magnetic resonance imaging). We also tested each participant on a 2-interval forced choice detection task using high-contrast, moving Gabor patches. We then measured and assessed the strength of relationships between participants’ residual vision in their blind field and in vivo neurotransmitter concentrations, as well as visually evoked functional magnetic resonance imaging activity in their hMT+. Levels of GABA and glutamate were also measured in a sensorimotor region, which served as a control. RESULTS: Magnetic resonance spectroscopy-derived GABA and glutamate concentrations in hMT+ (but not sensorimotor cortex) strongly predicted blind-field visual detection abilities. Performance was inversely related to levels of both inhibitory and excitatory neurotransmitters in hMT+ but, surprisingly, did not correlate with visually evoked blood oxygenation level–dependent signal change in this motion-sensitive region. CONCLUSIONS: Levels of GABA and glutamate in hMT+ appear to provide superior information about motion detection capabilities inside perimetrically defined blind fields compared to blood oxygenation level–dependent signal changes—in essence, serving as biomarkers for the quality of residual visual processing in the blind-field. Whether they also reflect a potential for successful rehabilitation of visual function remains to be determined

Microfabricated Probes for Studying Brain Chemistry: A Review

Probe techniques for monitoring in vivo chemistry (e.g., electrochemical sensors and microdialysis sampling probes) have significantly contributed to a better understanding of neurotransmission in correlation to behaviors and neurological disorders. Microfabrication allows construction of neural probes with high reproducibility, scalability, design flexibility, and multiplexed features. This technology has translated well into fabricating miniaturized neurochemical probes for electrochemical detection and sampling. Microfabricated electrochemical probes provide a better control of spatial resolution with multisite detection on a single compact platform. This development allows the observation of heterogeneity of neurochemical activity precisely within the brain region. Microfabricated sampling probes are starting to emerge that enable chemical measurements at high spatial resolution and potential for reducing tissue damage. Recent advancement in analytical methods also facilitates neurochemical monitoring at high temporal resolution. Furthermore, a positive feature of microfabricated probes is that they can be feasibly built with other sensing and stimulating platforms including optogenetics. Such integrated probes will empower researchers to precisely elucidate brain function and develop novel treatments for neurological disorders.Microfabricated neurochemical probes: Microfabrication technology emerges as an important tool for developing miniature, high precision probes for electrochemical detection and sampling from live brain tissues. This review describes advances and perspectives in adapting microfabrication to create the next generation of neurochemical probes.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144231/1/cphc201701180_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144231/2/cphc201701180.pd

Effects of visual attention on stereoscopic depth perception in the human visual cortex

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Mapping the visual world to the human brain

The visual maps measured non-invasively in the brain of human and non-human primates reliably reflect the underlying neuronal responses recorded with invasive electrodes

Comparison of neurochemical and BOLD signal contrast response functions in the human visual cortex

We investigated the relationship between neurochemical and hemodynamic responses as a function of image contrast in the human primary visual cortex (V1). Simultaneously acquired BOLD-fMRI and single voxel proton MR spectroscopy signals were measured in V1 of 24 healthy human participants of either sex at 7-Tesla field strength, in response to presentations (64 s blocks) of different levels of image contrast (3, 12.5, 50, 100%). Our results suggest that complementary measures of neurotransmission and energy metabolism are in partial agreement: BOLD and glutamate signals were linear with image contrast, however a significant increase in glutamate concentration was evident only at the highest intensity level. In contrast, GABA signals were steady across all intensity levels. These results suggest that neurochemical concentrations are maintained at lower ranges of contrast levels, which match the statistics of natural vision, and that high stimulus intensity may be critical to increase sensitivity to visually modulated glutamate siganls in the early visual cortex using MR spectroscopy

Effects of Spatial and Feature Attention on Disparity-Rendered Structure-From-Motion Stimuli in the Human Visual Cortex

<div><p>An important advance in the study of visual attention has been the identification of a non-spatial component of attention that enhances the response to similar features or objects across the visual field. Here we test whether this non-spatial component can co-select individual features that are perceptually bound into a coherent object. We combined human psychophysics and functional magnetic resonance imaging (fMRI) to demonstrate the ability to co-select individual features from perceptually coherent objects. Our study used binocular disparity and visual motion to define disparity structure-from-motion (dSFM) stimuli. Although the spatial attention system induced strong modulations of the fMRI response in visual regions, the non-spatial system’s ability to co-select features of the dSFM stimulus was less pronounced and variable across subjects. Our results demonstrate that feature and global feature attention effects are variable across participants, suggesting that the feature attention system may be limited in its ability to automatically select features within the attended object. Careful comparison of the task design suggests that even minor differences in the perceptual task may be critical in revealing the presence of global feature attention.</p></div

Stimuli and experimental paradigm.

<p>A: Structure-from-motion cylinders disambiguated by binocular disparity are perceived as rotating counter-clockwise (bottom left) or clockwise (bottom right) as controlled by the disparity of the right and left-wards moving surfaces (adapted from Dodd et al., 2001). B: Schematic diagram of the behavioral task used in the MRI-scanner, illustrating an example trial where attention is cued to the right side. For cued cylinders, participants reported whether the speed of rotation in the 1^st and 2^nd interval was different, while uncued cylinders were ignored.</p

Cortical responses to cylinders.

<p>A: Cortical responses to cylinders disambiguated by disparity under attended (open) and unattended (filled) conditions compared to a baseline of static dots with zero-disparity. B: Average BOLD response to attended cylinders disambiguated by disparity under clockwise (light gray) and counter-clockwise (dark gray) conditions compared to a baseline of static dots with zero-disparity. C: Average BOLD response to unattended cylinder when rotating in the same (light gray) or different (dark gray) directions to the attended cylinder compared to the baseline. All errors are ± s.e.m. averaged across left and right hemispheres and two scans within participant sessions.</p

Spatial attention increased BOLD response to cylinders.

<p>Icons on the top show a schematic view of the stimulus screen from the perspective of the participant. Left half of figure shows responses to two cylinders compared to a baseline composed of two fields of static zero-disparity dots, with attention directed to the left cylinder. The right half of the figure shows the same conditions with attention directed to the right cylinder. Borders of visual areas (white lines) were defined using standard retinotopic mapping. All data were fully cluster-corrected at p<0.05. The color bar indicates significance levels of activation maps with a z-statistic ranging from 2.3–12. The key gives the orientation of the flat patch in relation to the dorsal, ventral and medial axis. Light gray areas mark gyri, dark gray areas sulci.</p