Decreased Default Mode Network connectivity correlates with age-associated structural and cognitive changes

Ageing entails cognitive and motor decline as well as brain changes such as loss of gray (GM) and white matter (WM) integrity, neurovascular and functional connectivity alterations. Regarding connectivity, reduced resting-state fMRI connectivity between anterior and posterior nodes of the Default Mode Network (DMN) relates to cognitive function and has been postulated to be a hallmark of ageing. However, the relationship between age-related connectivity changes and other neuroimaging-based measures in ageing is fragmentarily investigated. In a sample of 116 healthy elders we aimed to study the relationship between antero-posterior DMN connectivity and measures of WM integrity, GM integrity and cerebral blood flow (CBF), assessed with an arterial spin labeling sequence. First, we replicated previous findings demonstrating DMN connectivity decreases in ageing and an association between antero-posterior DMN connectivity and memory scores. The results showed that the functional connectivity between posterior midline structures and the medial prefrontal cortex was related to measures of WM and GM integrity but not to CBF. Gray and WM correlates of anterio-posterior DMN connectivity included, but were not limited to, DMN areas and cingulum bundle. These results resembled patterns of age-related vulnerability which was studied by comparing the correlates of antero-posterior DMN with age-effect maps. These age-effect maps were obtained after performing an independent analysis with a second sample including both young and old subjects. We argue that antero-posterior connectivity might be a sensitive measure of brain ageing over the brain. By using a comprehensive approach, the results provide valuable knowledge that may shed further light on DMN connectivity dysfunctions in ageing

Down-Regulation of Negative Emotional Processing by Transcranial Direct Current Stimulation: Effects of Personality Characteristics

Evidence from neuroimaging and electrophysiological studies indicates that the left dorsolateral prefrontal cortex (DLPFC) is a core region in emotional processing, particularly during down-regulation of negative emotional conditions. However, emotional regulation is a process subject to major inter-individual differences, some of which may be explained by personality traits. In the present study we used transcranial direct current stimulation (tDCS) over the left DLPFC to investigate whether transiently increasing the activity of this region resulted in changes in the ratings of positive, neutral and negative emotional pictures. Results revealed that anodal, but not cathodal, tDCS reduced the perceived degree of emotional valence for negative stimuli, possibly due to an enhancement of cognitive control of emotional expression. We also aimed to determine whether personality traits (extraversion and neuroticism) might condition the impact of tDCS. We found that individuals with higher scores on the introversion personality dimension were more permeable than extraverts to the modulatory effects of the stimulation. The present study underlines the role of the left DLPFC in emotional regulation, and stresses the importance of considering individual personality characteristics as a relevant variable, although replication is needed given the limited sample size of our study

Multimodal characterization and modulation of large-scale memory networks: Implications for cognitive aging

[cat][eng

Down-regulation of negative emotional processing by transcranial direct current stimulation: effects of personality characteristics

Evidence from neuroimaging and electrophysiological studies indicates that the left dorsolateral prefrontal cortex (DLPFC) is a core region in emotional processing, particularly during down-regulation of negative emotional conditions. However, emotional regulation is a process subject to major inter-individual differences, some of which may be explained by personality traits. In the present study we used transcranial direct current stimulation (tDCS) over the left DLPFC to investigate whether transiently increasing the activity of this region resulted in changes in the ratings of positive, neutral and negative emotional pictures. Results revealed that anodal, but not cathodal, tDCS reduced the perceived degree of emotional valence for negative stimuli, possibly due to an enhancement of cognitive control of emotional expression. We also aimed to determine whether personality traits (extraversion and neuroticism) might condition the impact of tDCS. We found that individuals with higher scores on the introversion personality dimension were more permeable than extraverts to the modulatory effects of the stimulation. The present study underlines the role of the left DLPFC in emotional regulation, and stresses the importance of considering individual personality characteristics as a relevant variable, although replication is needed given the limited sample size of our study

Stimulus presentation protocol and examples of pictures used in the study.

<p>Before the presentation of each picture a white cross was shown on the screen for 4 seconds, followed by a positive, negative or neutral picture for 3 seconds, requiring emotional rating by the subject. Then another cross was presented for 4 seconds. Note that although the example contains pictures of the three emotional valences (positive, neutral, negative), during the experiment only one picture corresponding to a single emotional valence was presented at each time.</p

Comparison of tasks A and B in terms of the representation of valence and arousal dimensions.

<p>Each task consists of 180 stimuli, as described in the main text. Values are given in mean (SD).</p

Modulation of personality measures on tDCS effects.

<p>The scatterplot depicts a negative correlation between increasing scores of the extraversion dimension of personality (represented in the <i>x</i>-coordinate) and the tDCS-induced effects (represented in the <i>y</i>-coordinate) evaluated by the mean change of rating in negative emotional pictures between real and sham tDCS. Note that the tDCS modulation is higher the more the subjects manifest themselves as introverts.</p

Changes induced by real tDCS in the scores of emotional evaluations compared to sham tDCS.

<p>The values correspond to the mean change of rating between sham and real tDCS (and standard errors of mean), both anodal and cathodal, for each valence category. Only ratings for the negative emotional pictures under anodal left DLPFC were significantly different from sham (* p = 0.036, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022812#pone-0022812-t003" target="_blank">table 3</a>).</p

Experimental design.

<p>Each subject underwent sham and active stimulation on two different days in a counterbalanced design (see panel A). Two equivalent emotional processing tasks were used (A and B in the figure), which were randomized within subjects. For real tDCS, 20 min of 1mA was continuously applied whereas for the sham stimulation the current stimulator was turned only during the first 30 seconds, to mimic the somatic sensations without actually affecting the underlying cerebral cortex (see panel B).</p

Mean scores (and SD or p values) on mood variables (STAI, PANAS and VAS questionnaires).

<p>Only a significant Pre-Post decrease in nervousness VAS rating was found.</p