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 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

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

Method for Enhancing Cell Penetration of Gd³⁺-based MRI Contrast Agents by Conjugation with Hydrophobic Fluorescent Dyes

Gadolinium ion (Gd³⁺) complexes are commonly used as magnetic resonance imaging (MRI) contrast agents to enhance signals in <i>T</i>₁-weighted MR images. Recently, several methods to achieve cell-permeation of Gd³⁺ complexes have been reported, but more general and efficient methodology is needed. In this report, we describe a novel method to achieve cell permeation of Gd³⁺ complexes by using hydrophobic fluorescent dyes as a cell-permeability-enhancing unit. We synthesized Gd³⁺ complexes conjugated with boron dipyrromethene (<b>BDP-Gd</b>) and Cy7 dye (<b>Cy7-Gd</b>), and showed that these conjugates can be introduced efficiently into cells. To examine the relationship between cell permeability and dye structure, we further synthesized a series of <b>Cy7-Gd</b> derivatives. On the basis of MR imaging, flow cytometry, and ICP-MS analysis of cells loaded with <b>Cy7-Gd</b> derivatives, highly hydrophobic and nonanionic dyes were effective for enhancing cell permeation of Gd³⁺ complexes. Furthermore, the behavior of these <b>Cy7-Gd</b> derivatives was examined in mice. Thus, conjugation of hydrophobic fluorescent dyes appears to be an effective approach to improve the cell permeability of Gd³⁺ complexes, and should be applicable for further development of Gd³⁺-based MRI contrast agents

Petasin Activates AMP-Activated Protein Kinase and Modulates Glucose Metabolism

Petasin (<b>1</b>), a natural product found in plants of the genus <i>Petasites</i>, has beneficial medicinal effects, such as antimigraine and antiallergy activities. However, whether or not <b>1</b> modulates metabolic diseases is unknown. In this study, the effects of <b>1</b> on AMP-activated protein kinase (AMPK), which is considered a pharmacological target for treating metabolic diseases, are described. It was found that an extract of <i>Petasites japonicus</i> produces an increase in the phosphorylation of AMPK in vitro, and the main active compound <b>1</b> was isolated. When this compound was administered orally to mice, activation of AMPK in the liver, skeletal muscle, and adipose tissue was observed. Moreover, pretreatment with <b>1</b> enhanced glucose tolerance following the administration of a glucose solution to normal mice. The mechanism by which <b>1</b> activates AMPK was subsequently investigated, and an increased intracellular AMP/ATP ratio in the cultured cells treated with <b>1</b> occurred. In addition, treatment with petasin inhibited mitochondrial respiratory chain complex I. Taken together, the present results indicated that <b>1</b> modulates glucose metabolism and activates AMPK through the inhibition of mitochondrial respiration. The preclinical data suggested that petasin (<b>1</b>) could be useful for the treatment of metabolic diseases in humans

Characteristics of the study participants.

<p>Characteristics of the study participants.</p

Multiple logistic regression analysis of factors associated with sarcopenia.

<p>Multiple logistic regression analysis of factors associated with sarcopenia.</p