Biomedical subjects

Iole Indovina

Publications and source records attributed to Iole Indovina.

4 recordsLinked to original sources

PubMed2006

Dissociation of stimulus relevance and saliency factors during shifts of visuospatial attention.

The control of visuospatial attention entails multiple processes, including both voluntary (endogenous) factors and stimulus-driven (exogenous) factors. Exogenous processes can be triggered by visual targets presented at a previously unattended location, thus capturing attention in a stimulus-driven manner. However, little is known about the relative role of stimulus salience and behavioral relevance for this type of spatial reorienting. Here, we directly assessed how salience and relevance affect activation of the frontoparietal attentional system, using either low-salience but task-relevant target stimuli or salient but task-irrelevant flickering checkerboards. We compared event-related functional magnetic resonance imaging responses for stimuli presented at the unattended versus attended side (invalid minus valid trials), separately for the 2 categories of visual stimuli. We found that task-relevant invalid targets activated the frontoparietal attentional network, demonstrating that this system engages when target stimuli are presented at an unattended location, even when these have a low perceptual salience. Conversely, the presentation of high-salience checkerboards in one hemifield while endogenous attention was engaged elsewhere did not activate the attentional network. These findings indicate that task relevance is critical for stimulus-driven engagement of the attentional network when attentional resources are endogenously allocated somewhere else.

Adult↗

PubMed2005

Representation of visual gravitational motion in the human vestibular cortex.

How do we perceive the visual motion of objects that are accelerated by gravity? We propose that, because vision is poorly sensitive to accelerations, an internal model that calculates the effects of gravity is derived from graviceptive information, is stored in the vestibular cortex, and is activated by visual motion that appears to be coherent with natural gravity. The acceleration of visual targets was manipulated while brain activity was measured using functional magnetic resonance imaging. In agreement with the internal model hypothesis, we found that the vestibular network was selectively engaged when acceleration was consistent with natural gravity. These findings demonstrate that predictive mechanisms of physical laws of motion are represented in the human brain.

Acceleration↗

PubMed2004

Occipital-parietal interactions during shifts of exogenous visuospatial attention: trial-dependent changes of effective connectivity.

We studied neural interactions between brain areas involved in exogenous (stimulus-driven) control of visuospatial attention. With event-related functional magnetic resonance imaging (fMRI), we investigated changes of connectivity during shifts of spatial attention from an attended location to a previously unattended target location. Using a 3-T scanner, fMRI data were acquired from three healthy volunteers. According to a central visual cue, participants directed endogenous spatial attention to the left or the right visual hemifield for blocks of 56 s. Peripheral visual targets were presented unpredictably in either the attended hemifield (valid trials, 80%) or in the unattended hemifield (invalid trials, 20%) and participants performed a two-alternative forced-choice discrimination task with the target, irrespective of cue validity. In accordance with previous results, we found that the temporal-parietal junction (TPJ) mediates the shift of spatial attention toward stimuli presented at the unattended side (i.e., invalid trials). We critically studied the interaction between occipital areas responding to the visual stimuli and other brain regions in order to find regions functionally coupled with the occipital cortex during invalid trials. We found that the coupling between occipital areas processing visual stimuli and the TPJ selectively increased during invalid trials. Our results highlight how changes of connectivity between brain areas can describe attentional processes such as stimulus-driven shifts of spatial attention.

Adult↗

PubMed2003

Quantitative NumART2* mapping in functional MRI studies at 1.5 T.

Quantitative mapping of the effective transverse relaxation time, T2* and proton density was performed in a motor activation functional MRI (fMRI) study using multi-echo, echo planar imaging (EPI) and NumART2* (Numerical Algorithm for Real time T2*). Comparisons between NumART2* and conventional single echo EPI with an echo time of 64 ms were performed for five healthy participants examined twice. Simulations were also performed to address specific issues associated with the two techniques, such as echo time-dependent signal variation. While the single echo contrast varied with the baseline T2* value, relative changes in T2* remained unaffected. Statistical analysis of the T2* maps yielded fMRI activation patterns with an improved statistical detection relative to conventional EPI but with less activated voxels, suggesting that NumART2* has superior spatial specificity. Two effects, inflow and dephasing, that may explain this finding were investigated. Particularly, a statistically significant increase in proton density was found in a brain area that was detected as activated by conventional EPI but not by NumART2* while no such changes were observed in brain areas that showed stimulus correlated signal changes on T2* maps.

Algorithms↗