Using High Spatial Resolution to Improve BOLD fMRI Detection at 3T.

For different functional magnetic resonance imaging experiments using blood oxygenation level-dependent (BOLD) contrast, the acquisition of T2*-weighted scans at a high spatial resolution may be advantageous in terms of time-course signal-to-noise ratio and of BOLD sensitivity when the regions are prone to susceptibility artifacts. In this study, we explore this solution by examining how spatial resolution influences activations elicited when appetizing food pictures are viewed. Twenty subjects were imaged at 3 T with two different voxel volumes, 3.4 μl and 27 μl. Despite the diminution of brain coverage, we found that high-resolution acquisition led to a better detection of activations. Though known to suffer to different degrees from susceptibility artifacts, the activations detected by high spatial resolution were notably consistent with those reported in published activation likelihood estimation meta-analyses, corresponding to taste-responsive regions. Furthermore, these regions were found activated bilaterally, in contrast with previous findings. Both the reduction of partial volume effect, which improves BOLD contrast, and the mitigation of susceptibility artifact, which boosts the signal to noise ratio in certain regions, explained the better detection noted with high resolution. The present study provides further evidences that high spatial resolution is a valuable solution for human BOLD fMRI, especially for studying food-related stimuli

How is salt taste intensity encoded within the human brain? The responses of BOLD fMRI using food models

Functional MRI (fMRI) allows understanding the mechanisms by which sensations induced by food cues are perceived and processed within the brain, under the influence of various external (e.g. visual stimuli) and internal factors (e.g. body state). In particular, it allows analyzing at neurophysiological level how food formulations influence their sensory qualities and the pleasure experienced. Here, we used fMRI to infer several neural correlates of the perceived salty intensity produced by rewarding food models. Subjects received different savory solutions on their tongue using an MR-compatible gustatometer. The activations were mapped from smoothed high-resolution data, an imaging protocol providing good functional sensitivity in the gustatory cortex [1]. Two primary areas for taste processing were presumed in the human brain, intercepting the operculo-insular cortex and the lesser-known postcentral gyrus. We found highly significant neural correlates of salt taste intensity at the base of the postcentral gyrus bilaterally and to a lesser extent in the insula and the overlying operculi. This finding suggests that both primary areas were involved in salt taste intensity coding in human brain, which contrasts with previous results obtained with unpleasant salty solutions. We speculate that it may result from the use of rewarding food models, making it necessary to take specific account of the stimulation context for mimicking the brain’s integration of sensory rewards during normal feeding.[1] Iranpour J, Morrot G, Claise B, Jean B, Bonny J-M. Using high resolution to improve BOLD fMRI detection in gustatory cortices. Human Brain Mapping. Submitted

Voxel volume, magnetic field strength and echo time of studies included in the meta-analyses [28, 29] on the neural correlates of processing visual food cues.

<p>Voxel volume, magnetic field strength and echo time of studies included in the meta-analyses [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141358#pone.0141358.ref028" target="_blank">28</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141358#pone.0141358.ref029" target="_blank">29</a>] on the neural correlates of processing visual food cues.</p

Locations (MNI) of activated brain regions at the group level for the contrast between viewing food and non-food pictures obtained from HR data.

<p>The reported clusters were thresholded at the same <i>p</i> < 0.001 (uncorrected for multiple comparisons). <i>Q</i>_FDR indicates the level of FDR on clusters.</p

Metrics characterizing the fMRI activations at the individual level obtained in the two conditions of acquisition, LR and HR.

<p>Metrics characterizing the fMRI activations at the individual level obtained in the two conditions of acquisition, LR and HR.</p

Graphical outline of the stimulation protocol used in this fMRI experiment.

<p>Stimuli were presented according to a block design involving food-related and non-food-related blocks. During the presentation of food images, participants were asked to imagine the taste of the viewed food, as if they were actually eating it. Each image was separated by a fixation cross and a rest period was placed between two blocks.</p

Group statistical parametric maps for the comparison of significantly activated regions detected under LR and HR conditions for the contrast between viewing food and non-food pictures.

<p>Activations were successively shown in the OFC (y = 35/39), anterior insula (y = 3/6), amygdala (y = 0) and insula (y = -5/-9) using a voxel-wise p<0.001 uncorrected threshold, with an extent threshold of 5 voxels (neurologic orientation, right-on-right). Under such conditions, the activations observable in the left amygdala and right OFC with LR do not resist to the <i>Q</i>_FDR < 0.05 threshold used in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141358#pone.0141358.t002" target="_blank">Table 2</a>.</p

Masks showing the voxels contributing to the group analysis for the two conditions.

<p>Masks showing the voxels contributing to the group analysis for the two conditions.</p