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Nature Neuroscience Jun 2014Responses of sensory neurons differ across repeated measurements. This variability is usually treated as stochasticity arising within neurons or neural circuits....
Responses of sensory neurons differ across repeated measurements. This variability is usually treated as stochasticity arising within neurons or neural circuits. However, some portion of the variability arises from fluctuations in excitability due to factors that are not purely sensory, such as arousal, attention and adaptation. To isolate these fluctuations, we developed a model in which spikes are generated by a Poisson process whose rate is the product of a drive that is sensory in origin and a gain summarizing stimulus-independent modulatory influences on excitability. This model provides an accurate account of response distributions of visual neurons in macaque lateral geniculate nucleus and cortical areas V1, V2 and MT, revealing that variability originates in large part from excitability fluctuations that are correlated over time and between neurons, and that increase in strength along the visual pathway. The model provides a parsimonious explanation for observed systematic dependencies of response variability and covariability on firing rate.
Topics: Action Potentials; Animals; Female; Macaca fascicularis; Macaca mulatta; Macaca nemestrina; Male; Neurons; Photic Stimulation; Visual Cortex; Visual Pathways
PubMed: 24777419
DOI: 10.1038/nn.3711 -
AJNR. American Journal of Neuroradiology May 2022DTI studies of patients with primary open-angle glaucoma have demonstrated that glaucomatous degeneration is not confined to the retina but involves the entire visual...
BACKGROUND AND PURPOSE
DTI studies of patients with primary open-angle glaucoma have demonstrated that glaucomatous degeneration is not confined to the retina but involves the entire visual pathway. Due to the lack of direct biologic interpretation of DTI parameters, the structural nature of this degeneration is still poorly understood. We used neurite orientation dispersion and density imaging (NODDI) to characterize the microstructural changes in the pregeniculate optic tracts and the postgeniculate optic radiations of patients with primary open-angle glaucoma, to better understand the mechanisms underlying these changes.
MATERIALS AND METHODS
T1- and multishell diffusion-weighted scans were obtained from 23 patients with primary open-angle glaucoma and 29 controls. NODDI parametric maps were produced from the diffusion-weighted scans, and probabilistic tractography was used to track the optic tracts and optic radiations. NODDI parameters were computed for the tracked pathways, and the measures were compared between both groups. The retinal nerve fiber layer thickness and visual field loss were assessed for the patients with glaucoma.
RESULTS
The optic tracts of the patients with glaucoma showed a higher orientation dispersion index and a lower neurite density index compared with the controls (< .001 and = .001, respectively), while their optic radiations showed a higher orientation dispersion index only (= .003).
CONCLUSIONS
The pregeniculate visual pathways of the patients with primary open-angle glaucoma exhibited a loss of both axonal coherence and density, while the postgeniculate pathways exhibited a loss of axonal coherence only. Further longitudinal studies are needed to assess the progression of NODDI alterations in the visual pathways of patients with primary open-angle glaucoma across time.
Topics: Diffusion Magnetic Resonance Imaging; Diffusion Tensor Imaging; Glaucoma, Open-Angle; Humans; Leukoaraiosis; Neurites; Visual Pathways; White Matter
PubMed: 35450857
DOI: 10.3174/ajnr.A7495 -
Philosophical Transactions of the Royal... Oct 2016Studies are described which are intended to improve our understanding of the primary measurements made in non-invasive neural imaging. The blood oxygenation... (Review)
Review
Studies are described which are intended to improve our understanding of the primary measurements made in non-invasive neural imaging. The blood oxygenation level-dependent signal used in functional magnetic resonance imaging (fMRI) reflects changes in deoxygenated haemoglobin. Tissue oxygen concentration, along with blood flow, changes during neural activation. Therefore, measurements of tissue oxygen together with the use of a neural sensor can provide direct estimates of neural-metabolic interactions. We have used this relationship in a series of studies in which a neural microelectrode is combined with an oxygen micro-sensor to make simultaneous co-localized measurements in the central visual pathway. Oxygen responses are typically biphasic with small initial dips followed by large secondary peaks during neural activation. By the use of established visual response characteristics, we have determined that the oxygen initial dip provides a better estimate of local neural function than the positive peak. This contrasts sharply with fMRI for which the initial dip is unreliable. To extend these studies, we have examined the relationship between the primary metabolic agents, glucose and lactate, and associated neural activity. For this work, we also use a Doppler technique to measure cerebral blood flow (CBF) together with neural activity. Results show consistent synchronously timed changes such that increases in neural activity are accompanied by decreases in glucose and simultaneous increases in lactate. Measurements of CBF show clear delays with respect to neural response. This is consistent with a slight delay in blood flow with respect to oxygen delivery during neural activation.This article is part of the themed issue 'Interpreting BOLD: a dialogue between cognitive and cellular neuroscience'.
Topics: Animals; Brain Mapping; Cats; Cerebrovascular Circulation; Glucose; Lactic Acid; Magnetic Resonance Imaging; Neurons; Oxygen; Visual Pathways
PubMed: 27574310
DOI: 10.1098/rstb.2015.0357 -
NeuroImage May 2022Despite decades of research, our understanding of the relationship between color and form processing in the primate ventral visual pathway remains incomplete. Using fMRI...
Despite decades of research, our understanding of the relationship between color and form processing in the primate ventral visual pathway remains incomplete. Using fMRI multivoxel pattern analysis, we examined coding of color and form, using a simple form feature (orientation) and a mid-level form feature (curvature), in human ventral visual processing regions. We found that both color and form could be decoded from activity in early visual areas V1 to V4, as well as in the posterior color-selective region and shape-selective regions in ventral and lateral occipitotemporal cortex defined based on their univariate selectivity to color or shape, respectively (the central color region only showed color but not form decoding). Meanwhile, decoding biases towards one feature or the other existed in the color- and shape-selective regions, consistent with their univariate feature selectivity reported in past studies. Additional extensive analyses show that while all these regions contain independent (linearly additive) coding for both features, several early visual regions also encode the conjunction of color and the simple, but not the complex, form feature in a nonlinear, interactive manner. Taken together, the results show that color and form are encoded in a biased distributed and largely independent manner across ventral visual regions in the human brain.
Topics: Animals; Brain Mapping; Humans; Magnetic Resonance Imaging; Pattern Recognition, Visual; Photic Stimulation; Visual Cortex; Visual Pathways
PubMed: 35122966
DOI: 10.1016/j.neuroimage.2022.118941 -
Annual Review of Vision Science Sep 2018Inferior temporal cortex (IT) is a key part of the ventral visual pathway implicated in object, face, and scene perception. But how does IT work? Here, I describe an... (Review)
Review
Inferior temporal cortex (IT) is a key part of the ventral visual pathway implicated in object, face, and scene perception. But how does IT work? Here, I describe an organizational scheme that marries form and function and provides a framework for future research. The scheme consists of a series of stages arranged along the posterior-anterior axis of IT, defined by anatomical connections and functional responses. Each stage comprises a complement of subregions that have a systematic spatial relationship. The organization of each stage is governed by an eccentricity template, and corresponding eccentricity representations across stages are interconnected. Foveal representations take on a role in high-acuity object vision (including face recognition); intermediate representations compute other aspects of object vision such as behavioral valence (using color and surface cues); and peripheral representations encode information about scenes. This multistage, parallel-processing model invokes an innately determined organization refined by visual experience that is consistent with principles of cortical development. The model is also consistent with principles of evolution, which suggest that visual cortex expanded through replication of retinotopic areas. Finally, the model predicts that the most extensively studied network within IT-the face patches-is not unique but rather one manifestation of a canonical set of operations that reveal general principles of how IT works.
Topics: Animals; Color Perception; Facial Recognition; Humans; Models, Neurological; Temporal Lobe; Visual Cortex; Visual Pathways; Visual Perception
PubMed: 30059648
DOI: 10.1146/annurev-vision-091517-034202 -
Neurology(R) Neuroimmunology &... Mar 2020
Topics: Afferent Pathways; Gray Matter; Humans; Optic Neuritis; Visual Pathways
PubMed: 32229640
DOI: 10.1212/NXI.0000000000000667 -
Neuropsychologia Oct 2017A dominant view in the cognitive neuroscience of object vision is that regions of the ventral visual pathway exhibit some degree of category selectivity. However, recent... (Review)
Review
A dominant view in the cognitive neuroscience of object vision is that regions of the ventral visual pathway exhibit some degree of category selectivity. However, recent findings obtained with multivariate pattern analyses (MVPA) suggest that apparent category selectivity in these regions is dependent on more basic visual features of stimuli. In which case a rethinking of the function and organization of the ventral pathway may be in order. We suggest that addressing this issue of functional specificity requires clear coding hypotheses, about object category and visual features, which make contrasting predictions about neuroimaging results in ventral pathway regions. One way to differentiate between categorical and featural coding hypotheses is to test for residual categorical effects: effects of category selectivity that cannot be accounted for by visual features of stimuli. A strong method for testing these effects, we argue, is to make object category and target visual features orthogonal in stimulus design. Recent studies that adopt this approach support a feature-based categorical coding hypothesis according to which regions of the ventral stream do indeed code for object category, but in a format at least partially based on the visual features of stimuli.
Topics: Brain Mapping; Humans; Pattern Recognition, Visual; Photic Stimulation; Visual Cortex; Visual Pathways
PubMed: 28619529
DOI: 10.1016/j.neuropsychologia.2017.06.010 -
The Journal of Neuroscience : the... Aug 2019Visual information reaches the cerebral cortex through parallel ON and OFF pathways that signal the presence of light and dark stimuli in visual scenes. We have... (Comparative Study)
Comparative Study
Visual information reaches the cerebral cortex through parallel ON and OFF pathways that signal the presence of light and dark stimuli in visual scenes. We have previously demonstrated that optical blur reduces visual salience more for light than dark stimuli because it removes the high spatial frequencies from the stimulus, and low spatial frequencies drive weaker ON than OFF cortical responses. Therefore, we hypothesized that sustained optical blur during brain development should weaken ON cortical pathways more than OFF, increasing the dominance of darks in visual perception. Here we provide support for this hypothesis in humans with anisometropic amblyopia who suffered sustained optical blur early after birth in one of the eyes. In addition, we show that the dark dominance in visual perception also increases in strabismic amblyopes that have their vision to high spatial frequencies reduced by mechanisms not associated with optical blur. Together, we show that amblyopia increases visual dark dominance by 3-10 times and that the increase in dark dominance is strongly correlated with amblyopia severity. These results can be replicated with a computational model that uses greater luminance/response saturation in ON than OFF pathways and, as a consequence, reduces more ON than OFF cortical responses to stimuli with low spatial frequencies. We conclude that amblyopia affects the ON cortical pathway more than the OFF, a finding that could have implications for future amblyopia treatments. Amblyopia is a loss of vision that affects 2-5% of children across the world and originates from a deficit in visual cortical circuitry. Current models assume that amblyopia affects similarly ON and OFF visual pathways, which signal light and dark features in visual scenes. Against this current belief, here we demonstrate that amblyopia affects the ON visual pathway more than the OFF, a finding that could have implications for new amblyopia treatments targeted at strengthening a weak ON visual pathway.
Topics: Adolescent; Adult; Amblyopia; Brain; Cerebral Cortex; Darkness; Eye; Female; Fixation, Ocular; Humans; Light; Male; Middle Aged; Neuronal Plasticity; Photic Stimulation; Psychophysics; Thalamus; Vision, Monocular; Visual Acuity; Visual Pathways; Young Adult
PubMed: 31189574
DOI: 10.1523/JNEUROSCI.3215-18.2019 -
Neuroscience Bulletin Sep 2020
Topics: Animals; Humans; Vision, Binocular; Visual Cortex; Visual Pathways
PubMed: 32367252
DOI: 10.1007/s12264-020-00506-6 -
Frontiers in Neural Circuits 2019Understanding the mechanisms of vision in health and disease requires knowledge of the anatomy and physiology of the eye and the neural pathways relevant to visual... (Review)
Review
Understanding the mechanisms of vision in health and disease requires knowledge of the anatomy and physiology of the eye and the neural pathways relevant to visual perception. As such, development of imaging techniques for the visual system is crucial for unveiling the neural basis of visual function or impairment. Magnetic resonance imaging (MRI) offers non-invasive probing of the structure and function of the neural circuits without depth limitation, and can help identify abnormalities in brain tissues . Among the advanced MRI techniques, manganese-enhanced MRI (MEMRI) involves the use of active manganese contrast agents that positively enhance brain tissue signals in T1-weighted imaging with respect to the levels of connectivity and activity. Depending on the routes of administration, accumulation of manganese ions in the eye and the visual pathways can be attributed to systemic distribution or their local transport across axons in an anterograde fashion, entering the neurons through voltage-gated calcium channels. The use of the paramagnetic manganese contrast in MRI has a wide range of applications in the visual system from imaging neurodevelopment to assessing and monitoring neurodegeneration, neuroplasticity, neuroprotection, and neuroregeneration. In this review, we present four major domains of scientific inquiry where MEMRI can be put to imperative use - deciphering neuroarchitecture, tracing neuronal tracts, detecting neuronal activity, and identifying or differentiating glial activity. We deliberate upon each category studies that have successfully employed MEMRI to examine the visual system, including the delivery protocols, spatiotemporal characteristics, and biophysical interpretation. Based on this literature, we have identified some critical challenges in the field in terms of toxicity, and sensitivity and specificity of manganese enhancement. We also discuss the pitfalls and alternatives of MEMRI which will provide new avenues to explore in the future.
Topics: Animals; Brain; Contrast Media; Humans; Magnetic Resonance Imaging; Manganese; Neuroimaging; Neurosciences; Ophthalmology; Visual Pathways
PubMed: 31156399
DOI: 10.3389/fncir.2019.00035