scholarly journals Human visual gamma for color stimuli: When LGN drive is equalized, red is not special

2021 ◽  
Author(s):  
Benjamin J. Stauch ◽  
Alina Peter ◽  
Isabelle Ehrlich ◽  
Zora Nolte ◽  
Pascal Fries
Keyword(s):  
Visual Cortex ◽  
Human Subjects ◽  
Gamma Oscillations ◽  
Color Contrast ◽  
Color Processing ◽  
Thalamic Input ◽  
Early Visual Cortex ◽  
Input Source ◽  
Main Input ◽  
Input Strength

Strong gamma-band oscillations in primate early visual cortex can be induced by spatially homogeneous, high-contrast stimuli, such as color surfaces. Compared to other hues, particularly strong gamma oscillations have been reported for red stimuli. However, precortical color processing and the resultant strength of input to V1 has often not been fully controlled for. This leaves the possibility that stronger responses to some hues were due to differences in V1 input strength. We presented stimuli that had equal luminance and color contrast levels in a color coordinate system based on color responses of the lateral geniculate nucleus, the main input source for area V1. With these stimuli, we recorded magnetoencephalography in 30 human subjects. We found narrowband color-induced gamma oscillations in early visual cortex, which, contrary to previous reports, did not differ between red and green stimuli of equal L-M cone contrast. Notably, blue stimuli with contrast exclusively on the S cone axis induced very weak gamma responses, as well as smaller event-related fields and poorer change detection performance. The strength of human color gamma responses could be well explained by the strength of thalamic input induced by each hue and does not show a clear red bias when this input strength is properly equalized. 

scholarly journals Steady-State Visual Evoked Potentials Elicited from Early Visual Cortex Reflect Both Perceptual Color Space and Cone-Opponent Mechanisms

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Sae Kaneko ◽  
Ichiro Kuriki ◽  
Søren K Andersen
Keyword(s):  
Visual Cortex ◽  
Steady State ◽  
Evoked Potentials ◽  
Visual Evoked Potentials ◽  
Color Space ◽  
Color Contrast ◽  
Response Latencies ◽  
Opponent Color ◽  
Early Visual Cortex ◽  
Visual Evoked

Abstract Colors are represented in the cone-opponent signals, L-M versus S cones, at least up to the level of inputs to the primary visual cortex. We explored the hue selective responses in early cortical visual areas through recordings of steady-state visual evoked potentials (SSVEPs), elicited by a flickering checkerboard whose color smoothly swept around the hue circle defined in a cone-opponent color space. If cone opponency dominates hue representation in the source of SSVEP signals, SSVEP amplitudes as a function of hue should form a profile that is line-symmetric along the cardinal axes of the cone-opponent color space. Observed SSVEP responses were clearly chromatic ones with increased SSVEP amplitudes and reduced response latencies for higher contrast conditions. The overall elliptic amplitude profile was significantly tilted away from the cardinal axes to have the highest amplitudes in the “lime-magenta” direction, indicating that the hue representation in question is not dominated by cone-opponency. The observed SSVEP amplitude hue profile was better described as a summation of a perceptual response and cone-opponent responses with a larger weight to the former. These results indicate that hue representations in the early visual cortex, measured by the SSVEP technique, are possibly related to perceptual color contrast.

scholarly journals Color compensation in anomalous trichromats assessed with fMRI

2020 ◽  
Author(s):  
Katherine E.M. Tregillus ◽  
Zoey J. Isherwood ◽  
John E. Vanston ◽  
Stephen A. Engel ◽  
Donald I.A. MacLeod ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Neural Plasticity ◽  
Direct Evidence ◽  
Color Contrast ◽  
Response Functions ◽  
Cortical Responses ◽  
Early Visual Cortex ◽  
Color Compensation ◽  
Gain Adjustment ◽  
Contrast Response

AbstractAnomalous trichromacy is a common form of congenital color-deficiency resulting from a genetic alteration in the photopigments of the eye’s light receptors. The changes reduce sensitivity to reddish and greenish hues, yet previous work suggests that these observers may experience the world to be more colorful than their altered receptor sensitivities would predict, potentially indicating an amplification of post-receptoral signals. However, past evidence suggesting such a gain adjustment rests on subjective measures of color appearance or salience. We directly tested for neural amplification by using fMRI to measure cortical responses in color-anomalous and normal control observers. Color contrast response functions were measured in two experiments with different tasks to control for attentional factors. Both experiments showed a predictable reduction in chromatic responses for anomalous trichromats in primary visual cortex. However, in later areas V2v and V3v, chromatic responses in the two groups were indistinguishable. Our results provide direct evidence for neural plasticity that compensates for the deficiency in the initial receptor color signals and suggest that the site of this compensation is in early visual cortex.

scholarly journals Stimulus-specific plasticity in human visual gamma-band activity and functional connectivity

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Benjamin J Stauch ◽  
Alina Peter ◽  
Heike Schuler ◽  
Pascal Fries
Keyword(s):  
Visual Cortex ◽  
Human Subjects ◽  
Gamma Band ◽  
Stimulus Repetition ◽  
Oscillatory Dynamics ◽  
Early Visual Cortex ◽  
Neuronal Processing ◽  
Plastic Changes ◽  
Gamma Band Activity ◽  
Band Activity

Under natural conditions, the visual system often sees a given input repeatedly. This provides an opportunity to optimize processing of the repeated stimuli. Stimulus repetition has been shown to strongly modulate neuronal-gamma band synchronization, yet crucial questions remained open. Here we used magnetoencephalography in 30 human subjects and find that gamma decreases across ≈10 repetitions and then increases across further repetitions, revealing plastic changes of the activated neuronal circuits. Crucially, increases induced by one stimulus did not affect responses to other stimuli, demonstrating stimulus specificity. Changes partially persisted when the inducing stimulus was repeated after 25 minutes of intervening stimuli. They were strongest in early visual cortex and increased interareal feedforward influences. Our results suggest that early visual cortex gamma synchronization enables adaptive neuronal processing of recurring stimuli. These and previously reported changes might be due to an interaction of oscillatory dynamics with established synaptic plasticity mechanisms.

scholarly journals Neural Correlates of Sustained Spatial Attention in Human Early Visual Cortex

2007 ◽  
Vol 97 (1) ◽  
pp. 229-237 ◽  
Author(s):  
Michael A. Silver ◽  
David Ress ◽  
David J. Heeger
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Visual Stimulation ◽  
Human Subjects ◽  
Delay Period ◽  
Cortical Areas ◽  
Time Period ◽  
Variable Duration ◽  
Early Visual Cortex ◽  
Perceptual Performance

Attention is thought to enhance perceptual performance at attended locations through top-down attention signals that modulate activity in visual cortex. Here, we show that activity in early visual cortex is sustained during maintenance of attention in the absence of visual stimulation. We used functional magnetic resonance imaging (fMRI) to measure activity in visual cortex while human subjects performed a visual detection task in which a variable-duration delay period preceded target presentation. Portions of cortical areas V1, V2, and V3 representing the attended part of the visual field exhibited sustained increases in activity throughout the delay period. Portions of these cortical areas representing peripheral, unattended parts of the visual field displayed sustained decreases in activity. The data were well fit by a model that assumed the sustained neural activity was constant in amplitude over a time period equal to that of the actual delay period for each trial. These results demonstrate that sustained attention responses are present in early visual cortex (including primary visual cortex), in the absence of a visual stimulus, and that these responses correlate with the allocation of visuospatial attention in both the spatial and temporal domains.

Spectral Properties of Induced and Evoked Gamma Oscillations in Human Early Visual Cortex to Moving and Stationary Stimuli

2009 ◽  
Vol 102 (2) ◽  
pp. 1241-1253 ◽  
Author(s):  
J. B. Swettenham ◽  
S. D. Muthukumaraswamy ◽  
K. D. Singh
Keyword(s):  
Visual Cortex ◽  
Stimulus Presentation ◽  
Gamma Oscillations ◽  
Induced Response ◽  
Stimulus Motion ◽  
Time Frequency ◽  
Beta Power ◽  
Visual Areas ◽  
Gamma Power ◽  
Early Visual Cortex

In two experiments, magnetoencephalography (MEG) was used to investigate the effects of motion on gamma oscillations in human early visual cortex. When presented centrally, but not peripherally, stationary and moving gratings elicited several evoked and induced response components in early visual cortex. Time-frequency analysis revealed two nonphase locked gamma power increases—an initial, rapidly adapting response and one sustained throughout stimulus presentation and varying in frequency across observers from 28 to 64 Hz. Stimulus motion raised the sustained gamma oscillation frequency by a mean of ∼10 Hz. The largest motion-induced frequency increases were in those observers with the lowest gamma response frequencies for stationary stimuli, suggesting a possible saturation mechanism. Moderate gamma amplitude increases to moving versus stationary stimuli were also observed but were not correlated with the magnitude of the frequency increase. At the same site in visual cortex, sustained alpha/beta power reductions and an onset evoked response were observed, but these effects did not change significantly with the presence of motion and did not correlate with the magnitude of gamma power changes. These findings suggest that early visual areas encode moving and stationary percepts via activity at higher and lower gamma frequencies, respectively.

scholarly journals Superimposed gratings induce diverse response patterns of gamma oscillations in primary visual cortex

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bin Wang ◽  
Chuanliang Han ◽  
Tian Wang ◽  
Weifeng Dai ◽  
Yang Li ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Field Potential ◽  
Gamma Oscillations ◽  
Neural Mechanisms ◽  
Model Parameters ◽  
Response Patterns ◽  
Region Difference ◽  
High Gamma ◽  
Spiking Activity

AbstractStimulus-dependence of gamma oscillations (GAMMA, 30–90 Hz) has not been fully understood, but it is important for revealing neural mechanisms and functions of GAMMA. Here, we recorded spiking activity (MUA) and the local field potential (LFP), driven by a variety of plaids (generated by two superimposed gratings orthogonal to each other and with different contrast combinations), in the primary visual cortex of anesthetized cats. We found two distinct narrow-band GAMMAs in the LFPs and a variety of response patterns to plaids. Similar to MUA, most response patterns showed that the second grating suppressed GAMMAs driven by the first one. However, there is only a weak site-by-site correlation between cross-orientation interactions in GAMMAs and those in MUAs. We developed a normalization model that could unify the response patterns of both GAMMAs and MUAs. Interestingly, compared with MUAs, the GAMMAs demonstrated a wider range of model parameters and more diverse response patterns to plaids. Further analysis revealed that normalization parameters for high GAMMA, but not those for low GAMMA, were significantly correlated with the discrepancy of spatial frequency between stimulus and sites’ preferences. Consistent with these findings, normalization parameters and diversity of high GAMMA exhibited a clear transition trend and region difference between area 17 to 18. Our results show that GAMMAs are also regulated in the form of normalization, but that the neural mechanisms for these normalizations might differ from those of spiking activity. Normalizations in different brain signals could be due to interactions of excitation and inhibitions at multiple stages in the visual system.

Visual Cortex Alterations in Early and Late Blind Subjects During Tactile Perception

Perception ◽  
2021 ◽  
Vol 50 (3) ◽  
pp. 249-265
Author(s):  
A. Ankeeta ◽  
S. Senthil Kumaran ◽  
Rohit Saxena ◽  
Sada N. Dwivedi ◽  
Naranamangalam R. Jagannathan
Keyword(s):  
Visual Cortex ◽  
Children And Adolescents ◽  
Age Of Onset ◽  
Human Subjects ◽  
Functional Results ◽  
Blood Oxygen Level Dependent ◽  
Tactile Perception ◽  
Blood Oxygen Level ◽  
Sensory Motor ◽  
Post Hoc

Involvement of visual cortex varies during tactile perception tasks in early blind (EB) and late blind (LB) human subjects. This study explored differences in sensory motor networks associated with tactile task in EB and LB subjects and between children and adolescents. A total of 40 EB subjects, 40 LB subjects, and 30 sighted controls were recruited in two subgroups: children (6–12 years) and adolescents (13–19 years). Data were acquired using a 3T MR scanner. Analyses of blood oxygen level dependent (BOLD), functional connectivity (FC), correlation, and post hoc test for multiple comparisons were carried out. Difference in BOLD activity was observed in EB and LB groups in visual cortex during tactile perception, with increased FC of visual with dorsal attention and sensory motor networks in EB. EB adolescents exhibited increased connectivity with default mode and salience networks when compared with LB. Functional results correlated with duration of training, suggestive of better performance in EB. Alteration in sensory and visual networks in EB and LB correlated with duration of tactile training. Age of onset of blindness has an effect in cross-modal reorganization of visual cortex in EB and multimodal in LB in children and adolescents.

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