Hemifield columns co-opt ocular dominance column structure in human achiasma

In the absence of an optic chiasm, visual input to the right eye is represented in primary visual cortex (V1) in the right hemisphere, while visual input to the left eye activates V1 in the left hemisphere. Retinotopic mapping In V1 reveals that in each hemisphere left and right visual hemifield representations are overlaid (Hoffmann et al., 2012). To explain how overlapping hemifield representations in V1 do not impair vision, we tested the hypothesis that visual projections from nasal and temporal retina create interdigitated left and right visual hemifield representations in V1, similar to the ocular dominance columns observed in neurotypical subjects (Victor et al., 2000). We used high-resolution fMRI at 7 T to measure the spatial distribution of responses to left- and right-hemifield stimulation in one achiasmic subject. T_2-weighted 2D Spin Echo images were acquired at 0.8 mm isotropic resolution. The left eye was occluded. To the right eye, a presentation of flickering checkerboards alternated between the left and right visual fields in a blocked stimulus design. The participant performed a demanding orientation-discrimination task at fixation. A general linear model was used to estimate the preference of voxels in V1 to left- and right-hemifield stimulation. The spatial distribution of voxels with significant preference for each hemifield showed interdigitated clusters which densely packed V1 in the right hemisphere. The spatial distribution of hemifield-preference voxels in the achiasmic subject was stable between two days of testing and comparable in scale to that of human ocular dominance columns. These results are the first in vivo evidence showing that visual hemifield representations interdigitate in achiasmic V1 following a similar developmental course to that of ocular dominance columns in V1 with intact optic chiasm

Papez Circuit Activation Observed with Functional Imaging During Semantic List Learning in Healthy Adults

Brain Behavior and Cognitive Sciencehttp://deepblue.lib.umich.edu/bitstream/2027.42/63994/1/schallmo_michael-paul_2009.pd

Identifying separate components of surround suppression

xii,301 hlm

Abnormal contextual modulation of visual contour detection in patients with schizophrenia.

Schizophrenia patients demonstrate perceptual deficits consistent with broad dysfunction in visual context processing. These include poor integration of segments forming visual contours, and reduced visual contrast effects (e.g. weaker orientation-dependent surround suppression, ODSS). Background image context can influence contour perception, as stimuli near the contour affect detection accuracy. Because of ODSS, this contextual modulation depends on the relative orientation between the contour and flanking elements, with parallel flankers impairing contour perception. However in schizophrenia, the impact of abnormal ODSS during contour perception is not clear. It is also unknown whether deficient contour perception marks genetic liability for schizophrenia, or is strictly associated with clinical expression of this disorder. We examined contour detection in 25 adults with schizophrenia, 13 unaffected first-degree biological relatives of schizophrenia patients, and 28 healthy controls. Subjects performed a psychophysics experiment designed to quantify the effect of flanker orientation during contour detection. Overall, patients with schizophrenia showed poorer contour detection performance than relatives or controls. Parallel flankers suppressed and orthogonal flankers enhanced contour detection performance for all groups, but parallel suppression was relatively weaker for schizophrenia patients than healthy controls. Relatives of patients showed equivalent performance with controls. Computational modeling suggested that abnormal contextual modulation in schizophrenia may be explained by suppression that is more broadly tuned for orientation. Abnormal flanker suppression in schizophrenia is consistent with weaker ODSS and/or broader orientation tuning. This work provides the first evidence that such perceptual abnormalities may not be associated with a genetic liability for schizophrenia

Contour Detection Thresholds.

<p>Mean contour detection thresholds are plotted for 28 healthy controls (circles), 13 first-degree relatives (squares), and 25 patients with schizophrenia (triangles) for the Parallel (red), Random (gray), and Orthogonal (blue) conditions. Example contours with 4.5° jitter (bottom) and 31.5° jitter (top) are shown along the y-axis. Error bars are S.E.M. Double asterisk indicates significant differences in Random condition thresholds between schizophrenia patients and both healthy controls and first-degree relatives, single asterisk indicates a significant difference in Orthogonal condition thresholds between patients and relatives. Corrected for multiple comparisons via Tukey’s HSD, <i>p</i> < 0.05.</p