Dar Meshi

Hippocampal neurogenesis is not required for behavioral effects of environmental enrichment

Environmental enrichment increases adult hippocampal neurogenesis and alters hippocampal-dependent behavior in rodents. To investigate a causal link between these two observations, we analyzed the effect of enrichment on spatial learning and anxiety-like behavior while blocking adult hippocampal neurogenesis. We report that environmental enrichment alters behavior in mice regardless of their hippocampal neurogenic capability, providing evidence that the newborn cells do not mediate these effects of enrichment.

Genomewide Linkage Disequilibrium Mapping of Severe Bipolar Disorder in a Population Isolate

Genomewide association studies may offer the best promise for genetic mapping of complex traits. Such studies in outbred populations require very densely spaced single-nucleotide polymorphisms. In recently founded population isolates, however, extensive linkage disequilibrium (LD) may make these studies feasible with currently available sets of short tandem repeat markers, spaced at intervals as large as a few centimorgans. We report the results of a genomewide association study of severe bipolar disorder (BP-I), using patients from the isolated population of the central valley of Costa Rica. We observed LD with BP-I on several chromosomes; the most striking results were in proximal 8p, a region that has previously shown linkage to schizophrenia. This region could be important for severe psychiatric disorders, rather than for a specific phenotype.

The Emerging Neuroscience of Social Media

Social media use is a global phenomenon, with almost two billion people worldwide regularly using these websites. As Internet access around the world increases, so will the number of social media users. Neuroscientists can capitalize on the ubiquity of social media use to gain novel insights about social cognitive processes and the neural systems that support them. This review outlines social motives that drive people to use social media, proposes neural systems supporting social media use, and describes approaches neuroscientists can use to conduct research with social media. We close by noting important directions and ethical considerations of future research with social media.

How Expert Advice Influences Decision Making

People often use expert advice when making decisions in our society, but how we are influenced by this advice has yet to be understood. To address this, using functional magnetic resonance imaging, we provided expert and novice advice to participants during an estimation task. Participants reported that they valued expert advice more than novice advice, and activity in the ventral striatum correlated with this valuation, even before decisions with the advice were made. When using advice, participants compared their initial opinion to their advisor’s opinion. This comparison, termed the “opinion difference”, influenced advice utilization and was represented in reward-sensitive brain regions. Finally, the left lateral orbitofrontal cortex integrated both the size of the opinion difference and the advisor’s level of expertise, and average activity in this area correlated with mean advice utilization across participants. Taken together, these findings provide neural evidence for how advice engenders behavioral change during the decision-making process.

Sharing self-related information is associated with intrinsic functional connectivity of cortical midline brain regions.

Human beings are social animals and they vary in the degree to which they share information about themselves with others. Although brain networks involved in self-related cognition have been identified, especially via the use of resting-state experiments, the neural circuitry underlying individual differences in the sharing of self-related information is currently unknown. Therefore, we investigated the intrinsic functional organization of the brain with respect to participants’ degree of self-related information sharing using resting state functional magnetic resonance imaging and self-reported social media use. We conducted seed-based correlation analyses in cortical midline regions previously shown in meta-analyses to be involved in self-referential cognition: the medial prefrontal cortex (MPFC), central precuneus (CP), and caudal anterior cingulate cortex (CACC). We examined whether and how functional connectivity between these regions and the rest of the brain was associated with participants’ degree of self-related information sharing. Analyses revealed associations between the MPFC and right dorsolateral prefrontal cortex (DLPFC), as well as the CP with the right DLPFC, the left lateral orbitofrontal cortex and left anterior temporal pole. These findings extend our present knowledge of functional brain connectivity, specifically demonstrating how the brain’s intrinsic functional organization relates to individual differences in the sharing of self-related information.

Eye movements reset visual perception

Human vision uses saccadic eye movements to rapidly shift the sensitive foveal portion of our retina to objects of interest. For vision to function properly amidst these ballistic eye movements, a mechanism is needed to extract discrete percepts on each fixation from the continuous stream of neural activity that spans fixations. The speed of visual parsing is crucial because human behaviors ranging from reading to driving to sports rely on rapid visual analysis. We find that a brain signal associated with moving the eyes appears to play a role in resetting visual analysis on each fixation, a process that may aid in parsing the neural signal. We quantified the degree to which the perception of tilt is influenced by the tilt of a stimulus on a preceding fixation. Two key conditions were compared, one in which a saccade moved the eyes from one stimulus to the next and a second simulated saccade condition in which the stimuli moved in the same manner but the subjects did not move their eyes. We find that there is a brief period of time at the start of each fixation during which the tilt of the previous stimulus influences perception (in a direction opposite to the tilt aftereffect)--perception is not instantaneously reset when a fixation starts. Importantly, the results show that this perceptual bias is much greater, with nearly identical visual input, when saccades are simulated. This finding suggests that, in real-saccade conditions, some signal related to the eye movement may be involved in the reset phenomenon. While proprioceptive information from the extraocular muscles is conceivably a factor, the fast speed of the effect we observe suggests that a more likely mechanism is a corollary discharge signal associated with eye movement.

Accepting unfairness by a significant other is associated with reduced connectivity between medial prefrontal and dorsal anterior cingulate cortex

ABSTRACT Conflict is a ubiquitous feature of interpersonal relationships, yet many of these relationships preserve their value following conflict. Our ability to refrain from punishment despite the occurrence of conflict is a characteristic of human beings. Using a combination of behavioral and neuroimaging techniques, we show that prosocial decision-making is modulated by relationship closeness. In an iterated social exchange, participants were more likely to cooperate with their partner compared to an unknown person by accepting unfair exchanges. Importantly, this effect was not influenced by how resources were actually being shared with one’s partner. The medial prefrontal cortex (MPFC) was activated when the partner, rather than the unknown person, behaved unfairly and, in the same context, the MPFC demonstrated greater functional connectivity with the dorsal anterior cingulate cortex (DACC). MPFC–DACC connectivity was inversely associated with participants’ tendency to “forgive” their partner for unfairness as well as performance outside the scanner on a behavioral measure of forgiveness. We conclude that relationship closeness modulates a neural network comprising the MPFC/DACC during economic exchanges.

So Close to a Deal: Spatial-Distance Cues Influence Economic Decision-Making in a Social Context.

Social distance (i.e., the degree of closeness to another person) affects the way humans perceive and respond to fairness during financial negotiations. Feeling close to someone enhances the acceptance of monetary offers. Here, we explored whether this effect also extends to the spatial domain. Specifically, using an iterated version of the Ultimatum Game in a within-subject design, we investigated whether different visual spatial distance-cues result in different rates of acceptance of otherwise identical monetary offers. Study 1 found that participants accepted significantly more offers when they were cued with spatial closeness than when they were cued with spatial distance. Study 2 replicated this effect using identical procedures but different spatial-distance cues in an independent sample. Importantly, our results could not be explained by feelings of social closeness. Our results demonstrate that mere perceptions of spatial closeness produce analogous–but independent–effects to those of social closeness.

The Use of Recommendations on Physician Rating Websites: The Number of Raters Makes the Difference When Adjusting Decisions

ABSTRACT Physician rating websites allow users to check physicians’ profiles, write reviews, or rate their performance. The opinion of other users regarding a physician can affect our decision to visit her/him. To investigate the specific role of the number of users rating a physician when choosing a physician with support of these platforms, we used a Judge-Advisor System in which participants answered their likelihood to visit a physician before and after seeing the recommendations of others. Within the experiment, three conditions were presented: high and low number of reviewers recommending a physician, and no recommendations. We found that the participants’ likelihood to visit a physician varied with respect to the displayed physician characteristics on the platform. Importantly, after the recommendation of others was presented, participants’ likelihood to visit the physician changed significantly. The participants’ adjusted response was significantly closer to the recommendation coming from a higher number of users, which indicate that this online, social media cue influences our decision to visit physicians. Comments and ratings on physician ratings are generally positive, but we show that negative ratings have a direct negative influence in the decision to visit a physician. We suggest administrators of these platforms to pay special attention to the content that users upload.

Individual differences in social desirability are associated with white-matter microstructure of the external capsule

Humans tend to present themselves in a positive light to gain social approval. This behavioral trait, termed social desirability, is important for various types of social success. Surprisingly, investigation into the neural underpinnings of social desirability has been limited and focused only on interindividual differences in dopamine receptor binding. These studies revealed reduced dopamine receptor binding in the striatum of individuals who are high in trait social desirability. Interestingly, high dopamine signaling has been associated with low white-matter integrity, irrespective of social desirability. Based on these findings, we hypothesized that a positive association exists between trait social desirability and the white-matter microstructure of the external capsule, which carries fibers to the striatum from the prefrontal cortex. To test this hypothesis, we collected diffusion tensor imaging data and examined the relationship between fractional anisotropy of the external capsule and participants’ social desirability—our analysis revealed a positive association. As a second exploratory step, we examined the association between social desirability and white-matter microstructure throughout the whole brain. Our whole-brain analysis revealed associations within multiple major white-matter tracts, demonstrating that socially desirable behavior relies on connectivity between distributed brain regions.