Image_1_Within-Subject Correlation Analysis to Detect Functional Areas Associated With Response Inhibition.PDF

<p>Functional areas in fMRI studies are often detected by brain-behavior correlation, calculating across-subject correlation between the behavioral index and the brain activity related to a function of interest. Within-subject correlation analysis is also employed in a single subject level, which utilizes cognitive fluctuations in a shorter time period by correlating the behavioral index with the brain activity across trials. In the present study, the within-subject analysis was applied to the stop-signal task, a standard task to probe response inhibition, where efficiency of response inhibition can be evaluated by the stop-signal reaction time (SSRT). Since the SSRT is estimated, by definition, not in a trial basis but from pooled trials, the correlation across runs was calculated between the SSRT and the brain activity related to response inhibition. The within-subject correlation revealed negative correlations in the anterior cingulate cortex and the cerebellum. Moreover, the dissociation pattern was observed in the within-subject analysis when earlier vs. later parts of the runs were analyzed: negative correlation was dominant in earlier runs, whereas positive correlation was dominant in later runs. Regions of interest analyses revealed that the negative correlation in the anterior cingulate cortex, but not in the cerebellum, was dominant in earlier runs, suggesting multiple mechanisms associated with inhibitory processes that fluctuate on a run-by-run basis. These results indicate that the within-subject analysis compliments the across-subject analysis by highlighting different aspects of cognitive/affective processes related to response inhibition.</p

Dynamically Allocated Hub in Task-Evoked Network Predicts the Vulnerable Prefrontal Locus for Contextual Memory Retrieval in Macaques

<div><p>Neuroimaging and neurophysiology have revealed that multiple areas in the prefrontal cortex (PFC) are activated in a specific memory task, but severity of impairment after PFC lesions is largely different depending on which activated area is damaged. The critical relationship between lesion sites and impairments has not yet been given a clear mechanistic explanation. Although recent works proposed that a whole-brain network contains hubs that play integrative roles in cortical information processing, this framework relying on an anatomy-based structural network cannot account for the vulnerable locus for a specific task, lesioning of which would bring impairment. Here, we hypothesized that (i) activated PFC areas dynamically form an ordered network centered at a task-specific “functional hub” and (ii) the lesion-effective site corresponds to the “functional hub,” but not to a task-invariant “structural hub.” To test these hypotheses, we conducted functional magnetic resonance imaging experiments in macaques performing a temporal contextual memory task. We found that the activated areas formed a hierarchical hub-centric network based on task-evoked directed connectivity, differently from the anatomical network reflecting axonal projection patterns. Using a novel simulated-lesion method based on support vector machine, we estimated severity of impairment after lesioning of each area, which accorded well with a known dissociation in contextual memory impairment in macaques (impairment after lesioning in area 9/46d, but not in area 8Ad). The predicted severity of impairment was proportional to the network “hubness” of the virtually lesioned area in the task-evoked directed connectivity network, rather than in the anatomical network known from tracer studies. Our results suggest that PFC areas dynamically and cooperatively shape a functional hub-centric network to reallocate the lesion-effective site depending on the cognitive processes, apart from static anatomical hubs. These findings will be a foundation for precise prediction of behavioral impacts of damage or surgical intervention in human brains.</p></div

Hub-centric cortical network for temporal-order judgment.

<p>(A) PPI (MIDDLE > BOTH-END). Color <i>t</i>-map of PPI is superimposed on the inflated brain. Upper and lower panels show the PPI maps for the seeds in areas 10 and 9/46d, respectively. (B, C) Two bar plots in each column show <i>z</i>-values for PPIs from area 10 (B) or area 9/46d (C) to other ipsilateral homotopic areas (gray) and PPIs from other homotopic areas to area 10 (B) or area 9/46d (C) (white). Dashed lines indicate significant <i>z</i>-value (<i>p</i> = 0.05 [FDR correction]). * <i>p</i> < 0.05 (FDR correction). (D) PPI matrix among the ten homotopic areas. Rows and columns indicate seed and target areas, respectively. Significant connectivities are enclosed by thick black lines (<i>p</i> < 0.05 [FDR correction]). (E) Betweenness centralities of each area calculated based on (D). The dashed line indicates the significance at <i>p</i> = 0.05 (randomization test [comparison with the distribution of the randomized network]). * <i>p</i> < 0.05. (F) PPI matrix among the ten homotopic areas without assumptions of directionality. The weight of the connection between A and B is evaluated as the mean value of PPI_<i>A->B</i> and PPI_<i>B->A</i>. (G) Betweenness centralities of each area calculated based on (F). The dashed line indicates significance at <i>p</i> = 0.05 (randomization test). * <i>p</i> < 0.05. (H) Anatomical connectivity matrix among the ten homotopic areas. Rows and columns indicate seed and target areas, respectively. A white (black) square indicates the presence (absence) of anatomical connection from row to column. Anatomical information is based on the CoCoMac database [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#pbio.1002177.ref041" target="_blank">41</a>,<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#pbio.1002177.ref047" target="_blank">47</a>,<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#pbio.1002177.ref048" target="_blank">48</a>]. The projections to/from areas 8Ad, SEF, and LIP listed in the matrix are categorized as those to/from areas 8A, 6DR, and POa in CoCoMac, respectively. (I) Betweenness centralities of each area calculated based on (H). The dashed line indicates significance at <i>p</i> = 0.05 (randomization test). * <i>p</i> < 0.05.</p

Brain regions activated in MIDDLE minus BOTH-END contrast.

<p>Significant peaks at a voxel level of <i>p</i> < 0.05 corrected by FWE. Coordinates are listed in monkey bicommissural space [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#pbio.1002177.ref026" target="_blank">26</a>,<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#pbio.1002177.ref028" target="_blank">28</a>,<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#pbio.1002177.ref034" target="_blank">34</a>].</p><p>† Significant only at a voxel level of <i>p</i> < 0.001 corrected by false discovery rate (FDR).</p><p>‡ Significant only at a voxel level of <i>p</i> < 0.005 corrected by FDR.</p><p>* Homotopic area.</p><p># Nonhomotopic area but the area used for the PPI analysis with a larger set of areas in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#pbio.1002177.s011" target="_blank">S10 Fig</a> (see <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#sec010" target="_blank">Materials and Methods</a>).</p><p>10, area 10; 46, area 46; 9/46v, area 9/46 ventral part; 9/46d, area 9/46 dorsal part; 44/45B, area 44/45B; SEF, supplementary eye field; 8Ad, area 8A dorsal part; 8Av, area 8A ventral part; SMA, supplementary motor area; PMd, dorsal premotor area; PMv, ventral premotor area; 24c, area 24c; LIP, lateral intraparietal area; 5, area 5; S1, primary somatosensory cortex; 30, area 30; 23b, area 23b; TEa, area TEa; TPO, area TPO; PGa, area PGa; TEpd, area TEpd; TEO, area TEO; TFO, area TFO; V4, visual area 4; V3v, visual area 3 ventral part; Hip, hippocampus; Cd, caudate nucleus; SC, superior colliculus; ant, anterior; post, posterior; mid, middle.</p><p>Brain regions activated in MIDDLE minus BOTH-END contrast.</p

Temporal-order judgment task and behavioral performance of monkeys.

<p>(A) Trial structure in the temporal-order judgment task. In each trial, monkeys pulled a joystick to initiate the trial (Warning), after which a list of stimuli was presented serially (Cue). After a delay (Delay), two stimuli from the list were presented simultaneously (Choice). The monkeys were required to select the stimulus that had been presented more recently in the list. The time parameters and trial structure for monkey H are shown here. The stimuli were selected from a 1,200-picture pool of natural and artificial objects (from Microsoft Clip Art or HEMERA Photo-Object database) in a pseudorandom order. The images provided in this figure are representations only and were not used in the experiment. (B) Percentages of correct responses (upper) and reaction times (lower) for each monkey during scanning sessions. The dashed line indicates the chance level. Error bars indicate standard deviation (SD) across sessions. * <i>p</i> < 10⁻⁴, <i>t</i>-test. † <i>p</i> < 10⁻⁴, †† <i>p</i> < 10⁻⁵, ††† <i>p</i> < 10⁻⁷, paired <i>t</i>-test.</p

Brain regions active for temporal-order judgment.

<p>(A) Activity related to temporal-order judgment revealed by the contrast of MIDDLE minus BOTH-END. An activation map is superimposed on the inflated brain: top, lateral view; bottom, anterior view. Inset shows the atlas of the macaque prefrontal cortex based on Petrides (2005) [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#pbio.1002177.ref004" target="_blank">4</a>] and Petrides (1994) [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002177#pbio.1002177.ref046" target="_blank">46</a>]. <i>ps</i>, principal sulcus; <i>as sup</i>, superior branch of arcuate sulcus; <i>as inf</i>, inferior branch of arcuate sulcus. (B–D) Activation map is superimposed on transverse sections (B), coronal sections (C), and sagittal sections (D). LIP, lateral intraparietal area; SEF, supplementary eye field; Hip, hippocampus; <i>ips</i>, intraparietal sulcus; <i>sts</i>, superior temporal sulcus.</p

Dynamic reallocation of functional hub in response to demands of the delayed matching-to-sample task.

<p>(A) Trial structure in the DMS task. The monkeys were required to select the stimulus that had been presented as a sample stimulus. The stimuli of natural and artificial objects were chosen from Microsoft Clip Art or HEMERA Photo-Object database. The images provided in this figure are representations only and were not used in the experiment. (B) Percentages of correct responses (upper) and reaction times (lower) for each monkey. Behavioral performance of all the trials in the DMS task (yellow) is compared with that in the temporal-order judgment task (gray). The dashed line indicates the chance level. Error bars indicate SD across sessions. * <i>p</i> < 0.0003, † <i>p</i> < 0.002, <i>t</i>-test. (C) Brain regions active for the DMS task. Activation map is superimposed on coronal sections. (D) PPI matrix among the 15 homotopic areas identified in the DMS task. Rows and columns indicate seed and target regions, respectively. Significant connectivities are enclosed by thick black lines (<i>p</i> < 0.05 [FDR correction]). (E) Betweenness centralities of each area calculated based on (D). The dashed line indicates the significance at <i>p</i> < 0.05 (randomization test). * <i>p</i> < 0.05. (F) Anatomical connectivity matrix among the homotopic areas. Rows and columns indicate seed and target areas, respectively. A white (black) square indicates the presence (absence) of anatomical connection from row to column. Anatomical information is based on CoCoMac database. The areas to which the same labels are given in CoCoMac database area merged respectively. (G) Betweenness centralities of each area calculated based on (F). The dashed line indicates significance at <i>p</i> = 0.05 (randomization test). * <i>p</i> < 0.05.</p

Current amplitude dependence of the response magnitude of the cerebellar activation.

<p>(<b>a</b>) Average time course of the cerebellar activation in response to an individual EM block. The shaded region indicates the EM block. For each time course, the baseline signal [mean of 2 frames (5 sec) before the onset of EM block] was subtracted before averaging. Error bars indicate standard error (SE). Red, 750 µA (240 blocks). Green, 500 µA (264 blocks). Blue, 250 µA (240 blocks). (<b>b</b>) Response magnitude for each current amplitude. Colored lines indicate data for individual monkeys (gray solid line, Monkey 1; gray dotted line, Monkey 2). Error bars indicate SE. *, <i>P</i><0.02. **, <i>P</i><0.0002. ***, <i>P</i><10⁻⁸.</p

List of BOLD activations in the cerebellum.

<p>List of the coordinates of the peaks of EM-evoked BOLD activations in the cerebellum for two monkeys (Monkey 1, 250 µA, 30 runs; Monkey 2, 500 µA, 9 runs). Significance level was set at <i>P</i><0.05 (corrected). Activated regions with volumes ≥6 mm³ (2.1 original voxels) are included. Cb4, cerebellar lobule 4. Cb5, cerebellar lobule 5. Cb6, cerebellar lobule 6. Cop, copula pyramidis. Crus2, crus2 of ansiform lobule. DPFl, dorsal paraflocculus. PM, paramedian lobule. Anatomical areas are labeled by referring to the Paxinos et al. brain atlas <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047515#pone.0047515-Paxinos1" target="_blank">[22]</a>.</p

BOLD activations in the cerebellum induced by electrical stimulation of S1.

<p>(<b>a</b>)–(<b>b</b>) A representative <i>t</i>-score map of BOLD activation in Monkey 1 in one session (250 µA, 30 runs). (a) BOLD activation at the site of EM. In Monkey 1, right S1 was stimulated (arrow). (b) BOLD activations in the cerebellum. Cb5, cerebellar lobule V. Cop, copula myramidis. (<b>c</b>)–(<b>d</b>) A representative <i>t</i>-score map of BOLD activation in Monkey 2 in one session (500 µA, 9 runs). Conventions are the same as in (a) and (b). (c) BOLD activation at the site of EM. In Monkey 2, left S1 was stimulated (arrow). (d) BOLD activations in the cerebellum.</p