Diana I. Tamir

Comparative genomics of the lactic acid bacteria

Lactic acid-producing bacteria are associated with various plant and animal niches and play a key role in the production of fermented foods and beverages. We report nine genome sequences representing the phylogenetic and functional diversity of these bacteria. The small genomes of lactic acid bacteria encode a broad repertoire of transporters for efficient carbon and nitrogen acquisition from the nutritionally rich environments they inhabit and reflect a limited range of biosynthetic capabilities that indicate both prototrophic and auxotrophic strains. Phylogenetic analyses, comparison of gene content across the group, and reconstruction of ancestral gene sets indicate a combination of extensive gene loss and key gene acquisitions via horizontal gene transfer during the coevolution of lactic acid bacteria with their habitats.

Disclosing information about the self is intrinsically rewarding

Humans devote 30–40% of speech output solely to informing others of their own subjective experiences. What drives this propensity for disclosure? Here, we test recent theories that individuals place high subjective value on opportunities to communicate their thoughts and feelings to others and that doing so engages neural and cognitive mechanisms associated with reward. Five studies provided support for this hypothesis. Self-disclosure was strongly associated with increased activation in brain regions that form the mesolimbic dopamine system, including the nucleus accumbens and ventral tegmental area. Moreover, individuals were willing to forgo money to disclose about the self. Two additional studies demonstrated that these effects stemmed from the independent value that individuals placed on self-referential thought and on simply sharing information with others. Together, these findings suggest that the human tendency to convey information about personal experience may arise from the intrinsic value associated with self-disclosure.

Neural correlates of anchoring-and-adjustment during mentalizing

Recent studies have suggested that the medial prefrontal cortex (MPFC) contributes both to understanding the mental states of others and to introspecting about ones own mind. This finding has suggested that perceivers might use their own thoughts and feelings as a starting point for making inferences about others, consistent with “simulation” or “self-projection” views of social cognition. However, perceivers cannot simply assume that others think and feel exactly as they do; social cognition also must include processes that adjust for perceived differences between self and other. Recent cognitive work has suggested that such correction occurs through a process of “anchoring-and-adjustment” by which perceivers serially tune their inferences from an initial starting point based on their own introspections. Here, we used functional MRI to test two predictions derived from this anchoring-and-adjustment view. Participants (n = 64) used a Likert scale to judge the preferences of another person and to indicate their own preferences on the same items, allowing us to calculate the discrepancy between the participants answers for self and other. Whole-brain parametric analyses identified a region in the MPFC in which activity was related linearly to this self–other discrepancy when inferring the mental states of others. These findings suggest both that the self serves as an important starting point from which to understand others and that perceivers customize such inferences by serially adjusting away from this anchor.

Individual Differences in Risk Preference Predict Neural Responses during Financial Decision-Making

We investigated the neural correlates of subjective valuations during a task involving risky choices about lotteries. Because expected value was held constant across all lotteries, decisions were influenced by subjective preferences, which manifest behaviorally as risk-seeking or risk-averse attitudes. To isolate structures encoding risk preference during choice, we probed for areas showing increased activation as a function of selected risk-level. Such response patterns were obtained in anterior (ACC) and posterior cingulate cortex (PCC), superior frontal gyrus, caudate nucleus, and substantia nigra. Behavioral results revealed the presence of risk-averse and risk-neutral individuals. In parallel, brain signals revealed modulation of activity by risk attitude during choice. Correlations between risk-seeking attitudes and neural activity during risky choice were obtained in superior and inferior frontal gyri, medial and lateral orbitofrontal cortex, and parahippocampal gyrus, while correlations with risk-averse attitudes were found in the caudate. The dynamics of neural responses relevant to each stage of the task (decision, anticipation, outcome) were investigated via timeseries and conjunction analyses. Though the networks engaged in each of the task stages were mostly distinct, regions within ACC, PCC and caudate were consistently activated during each decision-making phase. These results demonstrate (1) that subjective assessments of risk, as well as individual attitudes toward risk, play a significant role in modulating activity within brain regions recruited during decision-making, and (2) that ACC, PCC and caudate are relevant during each phase of a decision-making task requiring subjective valuations, strengthening the role of these regions in self-referential subjective valuations during choice.

Anchoring and adjustment during social inferences

Simulation theories of social cognition suggest that people use their own mental states to understand those of others-particularly similar others. However, perceivers cannot rely solely on self-knowledge to understand another person; they must also correct for differences between the self and others. Here we investigated serial adjustment as a mechanism for correction from self-knowledge anchors during social inferences. In 3 studies, participants judged the attitudes of a similar or dissimilar person and reported their own attitudes. For each item, we calculated the discrepancy between responses for the self and other. The adjustment process unfolds serially, so to the extent that individuals indeed anchor on self-knowledge and then adjust away, trials with a large amount of self-other discrepancy should be associated with longer response times, whereas small self-other discrepancy should correspond to shorter response times. Analyses consistently revealed this positive linear relationship between reaction time and self-other discrepancy, evidence of anchoring-and-adjustment, but only during judgments of similar targets. These results suggest that perceivers mentalize about similar others using the cognitive process of anchoring-and-adjustment.

The default network distinguishes construals of proximal versus distal events

Humans enjoy a singular capacity to imagine events that differ from the “here-and-now.” Recent cognitive neuroscience research has linked such simulation processes to the brains “default network.” However, extant cognitive theories suggest that perceivers reliably simulate only relatively proximal experiences—those that seem nearby, soon, likely to happen, or relevant to a close other. Here, we test these claims by examining spontaneous engagement of the default network while perceivers consider experiencing events from proximal and distal perspectives. Across manipulations of perspective in four dimensions, two regions of the default network—medial prefrontal cortex and retrosplenial cortex—were more active for proximal than distal events, supporting cognitive accounts that perceivers only richly simulate experiences that seem immediate and that perceivers represent different dimensions of distance similarly. Moreover, stable individual differences in default activity when thinking about distal events correlated with individual variability in an implicit measure of psychological distance, suggesting that perceivers naturally vary in their tendency to simulate far-off or unlikely experiences.

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.

Neural evidence that three dimensions organize mental state representation: Rationality, social impact, and valence

Significance This study uses advanced functional neuroimaging analyses to test both existing and novel psychological theories about how we understand others’ minds. Analyses show that three dimensions—rationality, social impact, and valence—account for almost half of the variation in the neural representation of mental states, the most comprehensive theory to date regarding our ability to think about others’ minds. These findings both inform long-standing debates within social psychology about theory of mind and generate testable predictions about how our neural hardware supports our ability to mentalize. How do people understand the minds of others? Existing psychological theories have suggested a number of dimensions that perceivers could use to make sense of others’ internal mental states. However, it remains unclear which of these dimensions, if any, the brain spontaneously uses when we think about others. The present study used multivoxel pattern analysis (MVPA) of neuroimaging data to identify the primary organizing principles of social cognition. We derived four unique dimensions of mental state representation from existing psychological theories and used functional magnetic resonance imaging to test whether these dimensions organize the neural encoding of others’ mental states. MVPA revealed that three such dimensions could predict neural patterns within the medial prefrontal and parietal cortices, temporoparietal junction, and anterior temporal lobes during social thought: rationality, social impact, and valence. These results suggest that these dimensions serve as organizing principles for our understanding of other people.

Multivariate Pattern Analysis of Functional Magnetic Resonance Imaging Data Reveals Deficits in Distributed Representations in Schizophrenia

BACKGROUND Multivariate pattern analysis is an alternative method of analyzing functional magnetic resonance imaging (fMRI) data, which is capable of decoding distributed neural representations. We applied this method to test the hypothesis of the impairment in distributed representations in schizophrenia. We also compared the results of this method with traditional general linear model (GLM)-based univariate analysis. METHODS Nineteen schizophrenia and 15 control subjects viewed two runs of stimuli-exemplars of faces, scenes, objects, and scrambled images. To verify engagement with stimuli, subjects completed a 1-back matching task. A multivoxel pattern classifier was trained to identify category-specific activity patterns on one run of fMRI data. Classification testing was conducted on the remaining run. Correlation of voxelwise activity across runs evaluated variance over time in activity patterns. RESULTS Patients performed the task less accurately. This group difference was reflected in the pattern analysis results with diminished classification accuracy in patients compared with control subjects, 59% and 72%, respectively. In contrast, there was no group difference in GLM-based univariate measures. In both groups, classification accuracy was significantly correlated with behavioral measures. Both groups showed highly significant correlation between interrun correlations and classification accuracy. CONCLUSIONS Distributed representations of visual objects are impaired in schizophrenia. This impairment is correlated with diminished task performance, suggesting that decreased integrity of cortical activity patterns is reflected in impaired behavior. Comparisons with univariate results suggest greater sensitivity of pattern analysis in detecting group differences in neural activity and reduced likelihood of nonspecific factors driving these results.

Mental Simulation and Meaning in Life

Mental simulation, the process of self-projection into alternate temporal, spatial, social, or hypothetical realities is a distinctively human capacity. Numerous lines of research also suggest that the tendency for mental simulation is associated with enhanced meaning. The present research tests this association specifically examining the relationship between two forms of simulation (temporal and spatial) and meaning in life. Study 1 uses neuroimaging to demonstrate that enhanced connectivity in the medial temporal lobe network, a subnetwork of the brains default network implicated in prospection and retrospection, correlates with self-reported meaning in life. Study 2 demonstrates that experimentally inducing people to think about the past or future versus the present enhances self-reported meaning in life, through the generation of more meaningful events. Study 3 demonstrates that experimentally inducing people to think specifically versus generally about the past or future enhances self-reported meaning in life. Study 4 turns to spatial simulation to demonstrate that experimentally inducing people to think specifically about an alternate spatial location (from the present location) increases meaning derived from this simulation compared to thinking generally about another location or specifically about ones present location. Study 5 demonstrates that experimentally inducing people to think about an alternate spatial location versus ones present location enhances meaning in life, through meaning derived from this simulation. Study 6 demonstrates that simply asking people to imagine completing a measure of meaning in life in an alternate location compared with asking them to do so in their present location enhances reports of meaning. This research sheds light on an important determinant of meaning in life and suggests that undirected mental simulation benefits psychological well-being.