Callosal Connections of Primary Visual Cortex Predict the Spatial Spreading of Binocular Rivalry Across the Visual Hemifields

In binocular rivalry, presentation of different images to the separate eyes leads to conscious perception alternating between the two possible interpretations every few seconds. During perceptual transitions, a stimulus emerging into dominance can spread in a wave-like manner across the visual field. These traveling waves of rivalry dominance have been successfully related to the cortical magnification properties and functional activity of early visual areas, including the primary visual cortex (V1). Curiously however, these traveling waves undergo a delay when passing from one hemifield to another. In the current study, we used diffusion tensor imaging (DTI) to investigate whether the strength of interhemispheric connections between the left and right visual cortex might be related to the delay of traveling waves across hemifields. We measured the delay in traveling wave times (ΔTWT) in 19 participants and repeated this test 6 weeks later to evaluate the reliability of our behavioral measures. We found large interindividual variability but also good test–retest reliability for individual measures of ΔTWT. Using DTI in connection with fiber tractography, we identified parts of the corpus callosum connecting functionally defined visual areas V1–V3. We found that individual differences in ΔTWT was reliably predicted by the diffusion properties of transcallosal fibers connecting left and right V1, but observed no such effect for neighboring transcallosal visual fibers connecting V2 and V3. Our results demonstrate that the anatomical characteristics of topographically specific transcallosal connections predict the individual delay of interhemispheric traveling waves, providing further evidence that V1 is an important site for neural processes underlying binocular rivalry

Auditory Motion Capturing Ambiguous Visual Motion

In this study, it is demonstrated that moving sounds have an effect on the direction in which one sees visual stimuli move. During the main experiment sounds were presented consecutively at four speaker locations inducing left or rightward auditory apparent motion. On the path of auditory apparent motion, visual apparent motion stimuli were presented with a high degree of directional ambiguity. The main outcome of this experiment is that our participants perceived visual apparent motion stimuli that were ambiguous (equally likely to be perceived as moving left or rightward) more often as moving in the same direction than in the opposite direction of auditory apparent motion. During the control experiment we replicated this finding and found no effect of sound motion direction on eye movements. This indicates that auditory motion can capture our visual motion percept when visual motion direction is insufficiently determinate without affecting eye movements

Feature-Based Attention Affects Direction-Selective fMRI Adaptation in hMT+

Functional magnetic resonance adaptation has been successfully used to reveal direction-selective responses in the human motion complex (hMT+). Here, we aimed at further investigating direction-selective as well as position-selective responses of hMT+ by looking at how these responses are affected by feature-based attention. We varied motion direction and position of 2 consecutive random-dot stimuli. Participants had to either attend to the direction or the position of the stimuli in separate runs. We show that direction selectivity in hMT+ as measured by functional magnetic resonance imaging (fMRI) adaptation was strongly influenced by task set. Attending to the motion direction of the stimuli lead to stronger direction-selective fMRI adaptation than attending to their position. Position selectivity, on the other hand, was largely unaffected by attentional focus. Interestingly, the change in the direction-selective adaptation profile across tasks could not be explained by inheritance from earlier areas. The response pattern in the early retinotopic cortex was stable across conditions. In conclusion, our results provide further evidence for the flexible coding of direction information in hMT+ depending on task demand

Tumor Necrosis Factor-α Contributes to Ischemia- and Reperfusion-Induced Endothelial Activation in Isolated Hearts

During myocardial reperfusion, polymorphonuclear neutrophil (PMN) adhesion involving the intercellular adhesion molecule-1 (ICAM-1) may lead to aggravation and prolongation of reperfusion injury. We studied the role of early tumor necrosis factor-α (TNF-α) cleavage and nuclear factor-κB (NF-κB) activation on ICAM-1 expression and venular adhesion of PMN in isolated hearts after ischemia (15 minutes) and reperfusion (30 to 480 minutes). NF-κB activation (electromobility shift assay) was found after 30 minutes of reperfusion and up to 240 minutes. ICAM-1 mRNA, assessed by Northern blot, increased during the same interval. Functional effect of newly synthesized adhesion molecules was found by quantification (in situ fluorescence microscopy) of PMN, given as bolus after ischemia, which became adherent to small coronary venules (10 to 50 mm in diameter). After 480 minutes of reperfusion, ICAM-1–dependent PMN adhesion increased 2.5-fold compared with PMN adhesion obtained during acute reperfusion. To study the influence of NF-κB on PMN adhesion, we inhibited NF-κB activation by transfection of NF-κB decoy oligonucleotides into isolated hearts using HJV-liposomes. Decoy NF-κB but not control oligonucleotides blocked ICAM-1 upregulation and inhibited the subacute increase in PMN adhesion. Similar effects were obtained using BB 1101 (10 μg), an inhibitor of TNF-α cleavage enzyme. These data suggest that ischemia and reperfusion in isolated hearts cause liberation of TNF-α, activation of NF-κB, and upregulation of ICAM-1, an adhesion molecule involved in inflammatory response after ischemia and reperfusion