Prismatic adaptation changes visuospatial representation in the inferior parietal lobule.

Prismatic adaptation has been shown to induce a realignment of visuoproprioceptive representations and to involve parietocerebellar networks. We have investigated in humans how far other types of functions known to involve the parietal cortex are influenced by a brief exposure to prismatic adaptation. Normal subjects underwent an fMRI evaluation before and after a brief session of prismatic adaptation using rightward deviating prisms for one group or after an equivalent session using plain glasses for the other group. Activation patterns to three tasks were analyzed: (1) visual detection; (2) visuospatial short-term memory; and (3) verbal short-term memory. The prismatic adaptation-related changes were found bilaterally in the inferior parietal lobule when prisms, but not plain glasses, were used. This effect was driven by selective changes during the visual detection task: an increase in neural activity was induced on the left and a decrease on the right parietal side after prismatic adaptation. Comparison of activation patterns after prismatic adaptation on the visual detection task demonstrated a significant increase of the ipsilateral field representation in the left inferior parietal lobule and a significant decrease in the right inferior parietal lobule. In conclusion, a brief exposure to prismatic adaptation modulates differently left and right parietal activation during visual detection but not during short-term memory. Furthermore, the visuospatial representation within the inferior parietal lobule changes, with a decrease of the ipsilateral hemifield representation on the right and increase on the left side, suggesting thus a left hemispheric dominance

Multiple Networks for Interhemispheric Integration in the Visual Brain: fMRI BOLD Response Increases with EEG Synchronization

2006.05.6-12, ISMRM 2006, International Society for Magnetic Resonance in Medicine, 14th Scientific Meeting, Seattle, Washington, USA. Book of abstracts ELECTRONIC POSTER DISCUSSION: The Future of BOLD? Resting State Signals and Multiple Modalities: Electronic Poste

A Brief Exposure to Leftward Prismatic Adaptation Enhances the Representation of the Ipsilateral, Right Visual Field in the Right Inferior Parietal Lobule.

A brief exposure to rightward prismatic adaptation (PA) was shown to shift visual field representation within the inferior parietal lobule (IPL) from the right to the left hemisphere. This change in hemispheric dominance could be interpreted as (1) a general effect of discrepancy in visuomotor alignment caused by PA or (2) a direction-specific effect of rightward PA. To test these hypotheses, we compared the effects of rightward and leftward PA on visual representation in normal human subjects. Three groups of normal subjects underwent an fMRI evaluation using a simple visual detection task before and after brief PA exposure using leftward- or rightward-deviating prisms or no prisms (L-PA, R-PA, neutral groups). A two-way ANOVA group × session revealed a significant interaction suggesting that PA-induced modulation is direction specific. <i>Post hoc</i> analysis showed that L-PA enhanced the representation of the right visual field within the right IPL. Thus, a brief exposure to L-PA enhanced right hemispheric dominance within the ventral attentional system, which is the opposite effect of the previously described shift in hemispheric dominance following R-PA. The direction-specific effects suggest that the underlying neural mechanisms involve the fine-tuning of specific visuomotor networks. The enhancement of right hemispheric dominance following L-PA offers a parsimonious explanation for neglect-like symptoms described previously in normal subjects

A record of eruption and intrusion at a fast spreading ridge axis : axial summit trough of the East Pacific Rise at 9–10°N

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q10T07, doi:10.1029/2008GC002354.High-resolution side-scan sonar, near-bottom multibeam bathymetry, and deep-sea photo and bathymetry traverses are used to map the axial summit trough (AST) at the East Pacific Rise between 9 and 10°N. We define three ridge axis morphologic types: no AST, narrow AST, and wide AST, which characterize distinct ridge crest domains spanning tens of kilometers along strike. Near-bottom observations, modeling of deformation above intruding dikes, and comparisons to the geologic and geophysical structure of the ridge crest are used to develop a revised model of AST genesis and evolution. This model helps constrain the record of intrusive and extrusive magmatism and styles of lava deposition along the ridge crest at time scales from hundreds to tens of thousands of years. The grabens in the narrow-AST domain (9°43′–53′N) are consistent with deformation above the most recent (<10) diking events beneath the ridge crest. Frequent high–effusion rate extrusive volcanism in this domain (several eruptions every ∼100 years) overprints near-axis deformation and maintains a consistent AST width. The most recent eruption at the ridge crest occurred in this area and did not significantly modify the physical characteristics of the AST. The grabens in the wide-AST domain (9°23′–43′N) originated with similar dimensions to the narrow AST. Spreading, driven primarily by the intrusion of shallow dikes within a narrow axial zone, causes the initial graben bounding faults to migrate away from the axis. Infrequent extrusive volcanism (several eruptions every ∼1000 years) fills a portion of the subsidence that accumulates over time but does not significantly modify the width of the AST. Outside of these domains, lower–effusion rate constructional volcanism without efficient drain-back fills and erases the signature of the AST. The relative frequency of intrusive versus extrusive magmatic events controls the morphology of the ridge crest and appears to remain constant over millennial time scales within the domains we have identified; however, over longer time scales (∼10–25 ka), domain-specific intrusive-to-extrusive ratios do not appear to be fixed in space, resulting in a fairly consistent volcanic accretion over the length scale of the second-order ridge segment between 9°N and 10°N.This work was supported by NSF grants OCE-0525863 to D. Fornari and S. A. Soule; OCE-0732366 to S. A. Soule; and OCE-9819261 to H. Schouten, M. Tivey, and D. Fornari and by CNRS to J. Escartın

fMRI responses in medial frontal cortex that depend on the temporal frequency of visual input.

Functional networks in the human brain have been investigated using electrophysiological methods (EEG/MEG, LFP, and MUA) and steady-state paradigms that apply periodic luminance or contrast modulation to drive cortical networks. We have used this approach with fMRI to characterize a cortical network driven by a checkerboard reversing at a fixed frequency. We found that the fMRI signals in voxels located in occipital cortex were increased by checkerboard reversal at frequencies ranging from 3 to 14 Hz. In contrast, the response of a cluster of voxels centered on basal medial frontal cortex depended strongly on the reversal frequency, consistently exhibiting a peak in the response for specific reversal frequencies between 3 and 5 Hz in each subject. The fMRI signals at the frontal voxels were positively correlated indicating a homogeneous cluster. Some of the occipital voxels were positively correlated to the frontal voxels apparently forming a large-scale functional network. Other occipital voxels were negatively correlated to the frontal voxels, suggesting a functionally distinct network. The results provide preliminary fMRI evidence that during visual stimulation, input frequency can be varied to engage different functional networks

A brief exposure to rightward prismatic adaptation changes resting-state network characteristics of the ventral attentional system.

A brief session of rightward prismatic adaptation (R-PA) has been shown to alleviate neglect symptoms in patients with right hemispheric damage, very likely by switching hemispheric dominance of the ventral attentional network (VAN) from the right to the left and by changing task-related activity within the dorsal attentional network (DAN). We have investigated this very rapid change in functional organisation with a network approach by comparing resting-state connectivity before and after a brief exposure i) to R-PA (14 normal subjects; experimental condition) or ii) to plain glasses (12 normal subjects; control condition). A whole brain analysis (comprising 129 regions of interest) highlighted R-PA-induced changes within a bilateral, fronto-temporal network, which consisted of 13 nodes and 11 edges; all edges involved one of 4 frontal nodes, which were part of VAN. The analysis of network characteristics within VAN and DAN revealed a R-PA-induced decrease in connectivity strength between nodes and a decrease in local efficiency within VAN but not within DAN. These results indicate that the resting-state connectivity configuration of VAN is modulated by R-PA, possibly by decreasing its modularity

An fMRI study of error monitoring in Montessori and traditionally-schooled children.

The development of error monitoring is central to learning and academic achievement. However, few studies exist on the neural correlates of children's error monitoring, and no studies have examined its susceptibility to educational influences. Pedagogical methods differ on how they teach children to learn from errors. Here, 32 students (aged 8-12 years) from high-quality Swiss traditional or Montessori schools performed a math task with feedback during fMRI. Although the groups' accuracies were similar, Montessori students skipped fewer trials, responded faster and showed more neural activity in right parietal and frontal regions involved in math processing. While traditionally-schooled students showed greater functional connectivity between the ACC, involved in error monitoring, and hippocampus following correct trials, Montessori students showed greater functional connectivity between the ACC and frontal regions following incorrect trials. The findings suggest that pedagogical experience influences the development of error monitoring and its neural correlates, with implications for neurodevelopment and education