Blindsight relies on a functional connection between hMT+ and the lateral geniculate nucleus, not the pulvinar

<div><p>When the primary visual cortex (V1) is damaged, the principal visual pathway is lost, causing a loss of vision in the opposite visual field. While conscious vision is impaired, patients can still respond to certain images; this is known as ‘blindsight’. Recently, a direct anatomical connection between the lateral geniculate nucleus (LGN) and human motion area hMT+ has been implicated in blindsight. However, a functional connection between these structures has not been demonstrated. We quantified functional MRI responses to motion in 14 patients with unilateral V1 damage (with and without blindsight). Patients with blindsight showed significant activity and a preserved sensitivity to speed in motion area hMT+, which was absent in patients without blindsight. We then compared functional connectivity between motion area hMT+ and a number of structures implicated in blindsight, including the ventral pulvinar. Only patients with blindsight showed an intact functional connection with the LGN but not the other structures, supporting a specific functional role for the LGN in blindsight.</p></div

Seed region correlation maps for LGN and ventral pulvinar, in patients and controls.

<p>‘Seed regions’ are <b>(A)</b> LGN in the damaged hemisphere (left in controls), <b>(B)</b> ventral pulvinar in the damaged hemisphere (left in controls), <b>(C)</b> LGN in the undamaged hemisphere (right in controls), <b>(D)</b> ventral pulvinar in the undamaged hemisphere (right in controls). Results are shown separately for controls (left column), blindsight-positive patients (middle column), and blindsight-negative patients (right column). Mixed effects analyses, displayed on average high-resolution structural scans transformed to MNI space (radiological convention). Shaded blue areas are binarized Jülich-defined probabilistic maps of hMT+. LGN, lateral geniculate nucleus; MNI, Montreal Neurological Institute.</p

Seed region correlation maps for human motion area (hMT+), in patients and controls.

<p>‘Seed region’ is <b>(A)</b> hMT+ in the damaged hemisphere (left in controls) and <b>(B)</b> hMT+ in the undamaged hemisphere (right in controls). Results shown separately for controls (left column), blindsight-positive patients (middle column), and blindsight-negative patients (right column). Upper rows show axial slices through early visual cortex and hMT+; lower rows show coronal slices through LGN. Mixed effects analyses, displayed on average high-resolution structural scans, transformed to MNI space (radiological convention). Shaded green areas are binarized Jülich-defined probabilistic maps of LGN. LGN, lateral geniculate nucleus; MNI, Montreal Neurological Institute.</p

Functional connectivity of the visual pathways in patients and controls.

<p><b>(A)</b> Correlation of LGN and V1 in the same (undamaged) hemisphere over the entire fMRI timeseries, after stimulus-evoked activity has been regressed out. <b>(B)</b> Correlation of hMT+ bilaterally. Box plots show Fischer-corrected mean correlation coefficients comparing participant group ± SEM. Statistical symbols represent significance levels for one sample t-tests against baseline (zero): ε <i>p</i> ≤ 0.0001, * <i>p</i> < 0.001. Scatterplots are individual examples of fMRI signal in ROI1 versus ROI2. Each point represents a single fMRI volume. Plots for patients in <b>panel A</b> are correlations in the contralesional hemisphere. BS+ is blindsight positive, and BS- blindsight negative. Underlying data can be found in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2005769#pbio.2005769.s009" target="_blank">S2 Data</a>. fMRI, functional MRI; LGN, lateral geniculate nucleus; ROI, region of interest; SEM, standard error of the mean; V1, primary visual cortex.</p

fMRI responses to motion for patients with V1 lesions and controls.

<p>Results are shown separately for <b>(A)</b> blindsight-positive patients, <b>(B)</b> blindsight-negative patients, and <b>(C)</b> healthy controls. <b>(i)</b> Significant activity for moving versus static dots in the blind right hemifield of patients with left V1 lesions and <b>(ii)</b> the blind left hemifield of patients with right V1 lesions. Mixed effects analyses, <i>P</i> < 0.001 uncorrected for a priori regions of interest, elsewhere cluster-corrected <i>p</i> < 0.01. Shaded blue areas are binarized Jülich-defined probabilistic maps of hMT+, radiological convention. <b>(iii)</b> Mean contralateral hMT+ signal change averaged across all five stimulus conditions, comparing sighted (blue) and blind (red) hemifields ± SEM. In controls, ‘Left HF’ refers to left hemifield, ‘Right HF’ is right hemifield. * significant activity above baseline <i>p</i> < 0.05, ψ <i>p</i> ≤ 0.001, ns = not significant. <i>P</i> values are from <i>t</i> tests. <b>(iv)</b> Mean signal change in contralateral hMT+ as a function of stimulus speed, shown separately for each hemifield (blue squares are sighted hemifield, red diamonds are blind hemifield). Responses to static stimuli are dotted (left/sighted hemifield) or dashed (right/blind hemifield) lines. Underlying data for iii and iv can be found in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2005769#pbio.2005769.s008" target="_blank">S1 Data</a>. fMRI, functional MRI; SEM, standard error of the mean; V1, primary visual cortex.</p

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

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

Mean classification accuracy to cylinders.

<p>A: Mean classification accuracy to a cylinder (in left or right visual field) in the 100 most activated voxels V1 and other retinotopic visual areas (B–G). The white bars show the classification based on attended or unattended condition. Light gray bars indicate the classification of an attended cylinder rotating in a clockwise or counter-clockwise direction. Dark gray bars show the classification of the unattended cylinder rotating in the same or different direction as the attended cylinder. The black line at 0.5 indicates chance performance. Black error bars indicate Bonferroni-corrected 95% confidence intervals obtained by iterating the classification 10000 times. Red lines indicate Bonferroni-corrected 95% confidence intervals of the empirical null distribution obtained by iterating the classification with permuted labels 10000 times. Asterices indicate significant classification accuracy.</p

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