Brain Mechanisms of Persuasion: How "Expert Power" Modulates Memory and Attitudes

Human behavior is affected by various forms of persuasion. The general persuasive effect of high expertise of the communicator, often referred to as "expert power", is well documented. We found that a single exposure to a combination of an expert and an object leads to a long-lasting positive effect on memory for and attitude towards the object. Using functional magnetic resonance imaging (fMRI), we probed the neural processes predicting these behavioral effects. Expert context was associated with distributed left-lateralized brain activity in prefrontal and temporal cortices related to active semantic elaboration. Furthermore, experts enhanced subsequent memory effects in the medial temporal lobe (i.e. in hippocampus and parahippocampal gyrus) involved in memory formation. Experts also affected subsequent attitude effects in the caudate nucleus involved in trustful behavior, reward processing and learning. These results may suggest that the persuasive effect of experts is mediated by modulation of caudate activity resulting in a re-evaluation of the object in terms of its perceived value. Results extend our view of the functional role of the dorsal striatum in social interaction and enable us to make the first steps toward a neuroscientific model of persuasion.neuroeconomics;social influence;attitude;expertise;persuasion;celebrities;memory encoding

Hippocampus guides adaptive learning during dynamic social interactions

How do we evaluate whether someone will make a good friend or collaborative peer? A hallmark of human cognition is the ability to make adaptive decisions based on information garnered from limited prior experiences. Using an interactive social task measuring adaptive choice (deciding who to reengage or avoid) in male and female participants, we find the hippocampus supports value-based social choices following single-shot learning. These adaptive choices elicited a suppression signal in the hippocampus, revealing sensitivity for the subjective perception of a person and how well they treat you during choice. The extent to which the hippocampus was suppressed was associated with flexibly interacting with prior generous individuals and avoiding selfish individuals. Further, we found that hippocampal signals during decision-making were related to subsequent memory for a person and the offer they made before. Consistent with the hippocampus leveraging previously executed choices to solidify a reliable neural signature for future adaptive behavior, we also observed a later hippocampal enhancement. These findings highlight the hippocampus playing a multifaceted role in socially adaptive learning

Adaptive task difficulty influences neural plasticity and transfer of training

The efficacy of cognitive training is controversial, and research progress in the field requires an understanding of factors that promote transfer of training gains and their relationship to changes in brain activity. One such factor may be adaptive task difficulty, as adaptivity is predicted to facilitate more efficient processing by creating a prolonged mismatch between the supply of, and the demand upon, neural resources. To test this hypothesis, we measured behavioral and neural plasticity in fMRI sessions before and after 10 sessions of working memory updating (WMU) training, in which the difficulty of practiced tasks either adaptively increased in response to performance or was fixed. Adaptive training resulted in transfer to an untrained episodic memory task and activation decreases in striatum and hippocampus on a trained WMU task, and the amount of training task improvement was associated with near transfer to other WMU tasks and with hippocampal activation changes on both near and far transfer tasks. These findings suggest that cognitive training programs should incorporate adaptive task difficulty to broaden transfer of training gains and maximize efficiency of task-related brain activity

Aging and functional reorganization of striatum- and Medial-Temporal Lobe-dependent memory systems

Bisherige Forschung hat zwischen zwei Gedächtnissystemen unterschieden: dem sog. deklarativen Gedächtnis (DG), welches sich durch die Fähigkeit vergangene Lebensereignisse bewusst zu erinnern auszeichnet und mit dem lobus temporalis medialis (MTL) in Verbindung steht, und dem prozeduralen Gedächtnis (PG), welches erlernte Fertigkeiten beinhaltet und mit dem Corpus striatum assoziiert ist. Weitere Studien haben ergeben, dass Alterung von neurologischen Schäden in beiden Systemen, erhöhter Aktivität im MTL und einer relativ geringeren Beeinträchtigung des PG begleitet ist. Hyperaktivität im MTL wurde dabei sowohl mit verbesserten als auch verschlechterten Gedächtnisleistungen in Verbindung gebracht. Die hier vorgelegte Dissertation befasst sich mit dem Einfluss von Alterung auf die Beziehungen zwischen o. g. Hirnnetzwerken und prozeduralen bzw. deklarativen Gedächtnisfähigkeiten. Studie I zeigte, dass Altersunterschiede in einer prozeduralen Gedächtnisaufgabe graduell im Verlaufe des Trainings entstehen und vmtl. mit negativen Einflüssen von Alterung auf den Übergang von PG zu DG in Zusammenhang stehen. Zwei striatal-dopaminerge genetische Polymorphismen, rs907094 auf DARPP-32 und VNTR auf DAT, wirkten sich dabei auf das DG älterer aber nicht jüngerer Erwachsener aus. In Studie II wurden Beeinträchtigungen im neuronalen Vorhersagefehler, einem neuronales Lernsignal im Striatum, in älteren Probanden gefunden. Studie III konnte teilweise intaktes PG in einer räumlichen Gedächtnisaufgabe demonstrieren, wobei der Polymorphismus rs17070145 auf WWC1, der sich auf Lanzeitpotenzierung im MTL auswirkt, diese Altersunterschiede modulierte. In Studie IV wurden neuronale Repräsentationen und Komputationen während einer räumlichen Gedächtnisaufgabe untersucht. Während jüngere Probanden in dieser Studie Anzeichen von MTL-basiertem DG zeigten, zeigten ältere Teilnehmer Evidenz von PG. Die neuronalen Signaturen älterer Erwachsener wurden jedoch am stärksten im MTL beobachtet.Previous research has distinguished between a declarative memory system that stores flexible representations and is subserved by the medial-temporal lobe (MTL) and a procedural memory system that expresses past experiences through skills and is based mainly on the striatum. Investigations into age-related changes in these memory systems indicated a complex pattern of neural degradation in both systems, elevated MTL activity as well as partially spared procedural memory functions in older adults. A literature review further suggests that MTL overactivity can be caused by factors which are either beneficial or detrimental for memory. The present dissertation investigated the effects of human aging on the relations of brain functions to declarative and procedural memory. In Study I, age differences in a procedural memory task gradually emerged over the course of training and were linked to negative effects of aging on the transition from procedural to declarative memory. In addition, this study showed that striatal dopaminergic genetic polymorphisms, rs907094 on DARPP-32 and VNTR on DAT, affected declarative knowledge in older but not younger adults. Study II indicated that prediction error signals in the human brain, a neural computation associated with striatal learning functions, were partially impaired in older adults. Study III demonstrated partially intact procedural memory in older adults in a spatial memory task, whereby age differences were modulated by a polymorphism influencing long-term potentiation in the MTL (rs17070145 on WWC1). Finally, Study IV showed hat that neural representations and computations subserving spatial memory qualitatively differed between younger and older adults. The performance and neural activation of younger adults showed unique properties of MTL-dependent declarative memory. Older adults, in contrast, showed behavioral and neural indications of procedural memory but the localization of the neural signatures peaked in the MTL

Sleep-dependent consolidation in multiple memory systems

Before newly formed memories can last for the long-term, they must undergo a period of consolidation. It has been shown that sleep facilitates this process. One hypothesis about how this may occur is that learning-related neuronal activity is replayed during following sleep periods. Such a reactivation of neural activity patterns has been repeatedly shown in the hippocampal formation in animals. Hippocampally-induced reactivation can also be observed in other brain areas like the neocortex and basal ganglia. On the behavioral level, sleep has been found to benefit performance on a broad range of memory tasks that rely on different neural systems. Up to now, however, it is unclear whether the same mechanisms mediate effects of sleep on consolidation in different memory systems. In this thesis, we investigated both the effects and the mechanisms of sleep-dependent consolidation in multiple memory systems. We find that sleep benefits performance on a broad range of procedural and declarative memory tasks (studies 1 and 2). These beneficial effects of sleep go beyond a reduction of retroactive interference as effected by quiet wakeful meditation (study 1). In study 2, we demonstrate that the processes underlying these beneficial effects of sleep are different for different memory systems. We assessed performance on typical declarative and procedural memory tasks during one week after participants slept or were sleep deprived for one night after learning. Sleep-dependent consolidation of hippocampal and non-hippocampal memory follows different time-courses. Hippocampal memory shows a benefit of sleep only one day after learning. Performance after sleep deprivation recovers following the next night of sleep, so that no enduring effect of sleep can be observed. However, sleep deprivation before recall does not impair performance. For non-hippocampal memory, on the other hand, long-term benefits of sleep after learning can be observed even after four days. Here, delayed sleep cannot rescue performance. This indicates a dissociation between two sleep-related consolidation mechanisms, which rely on distinct neuronal processes. We studied the neuronal processes underlying sleep effects on declarative memory in study 3, where we investigate learning-related electrophysiological activity in the sleeping brain. With the help of multivariate pattern classification algorithms, we show that brain activity during sleep contains information about the kind of visual stimuli that were learned earlier. We thus find that learned material is actively reprocessed during sleep. In a next step, we examined whether procedural memory can also benefit from reactivation during sleep. We find that a procedural memory task that has been found to activate the hippocampus can be strengthened by externally cueing the reactivation process during sleep. Similar to study 2, this indicates that it is not the traditional distinction between declarative and procedural memory that determines how memories are consolidated during sleep. Rather, memory systems, and in particular hippocampal contribution, decide the sleep-dependent consolidation process. In the first four studies, we examined how sleep affects memory in different memory systems. In our last study, we went one step further and investigated whether multiple memory systems can also interact during consolidation in sleep. We devised a task during which both implicit and explicit memory develop during learning. Results show that sleep not only strengthens implicit and explicit memory individually, it also integrates these formerly separate representations of the learning task. Implicit and explicit memory are negatively correlated immediately after training. Sleep renders this association positive and allows cooperation between the two memory traces. We observe this change both in behavior, using structural equation modeling, and on the level of brain activity, measured by fMRI. After sleep, the hippocampus is more strongly activated during recall of implicit memory, whereas the caudate nucleus shows stronger activity during explicit memory recall. Moreover, both regions show correlated stimulus-induced responses in a task that allows memory systems cooperation. These results provide conclusive evidence that sleep not only strengthens memory, but also reorganizes the contributing neural circuits. In this way, sleep actually changes the quality of the memory representation

Functional MRI investigations of overlapping spatial memories and flexible decision-making in humans

Thesis (Ph.D.)--Boston UniversityResearch in rodents and computational modeling work suggest a critical role for the hippocampus in representing overlapping memories. This thesis tested predictions that the hippocampus is important in humans for remembering overlapping spatial events, and that flexible navigation of spatial routes is supported by key prefrontal and striatal structures operating in conjunction with the hippocampus. The three experiments described in this dissertation used functional magnetic resonance imaging (fMRI) in healthy young people to examine brain activity during context-dependent navigation of virtual maze environments. Experiment 1 tested whether humans recruit the hippocampus and orbitofrontal cortex to successfully retrieve well-learned overlapping spatial routes. Participants navigated familiar virtual maze environments during fMRI scanning. Brain activity for flexible retrieval of overlapping spatial memories was contrasted with activity for retrieval of distinct non-overlapping memories. Results demonstrate the hippocampus is more strongly recruited for planning and retrieval of overlapping routes than non-overlapping routes, and the orbitofrontal cortex is recruited specifically for context-dependent navigational decisions. Experiment 2 examined whether the hippocampus, orbitofrontal cortex, and striatum interact cooperatively to support flexible navigation of overlapping routes. Using a functional connectivity analysis of fMRI data, we compared interactions between these structures during virtual navigation of overlapping and non-overlapping mazes. Results demonstrate the hippocampus interacts with the caudate more strongly for navigating overlapping than non-overlapping routes. Both structures cooperate with the orbitofrontal cortex specifically during context-dependent decision points, suggesting the orbitofrontal cortex mediates translation of contextual information into the flexible selection of behavior. Experiment 3 examined whether the hippocampus and caudate contribute to forming context-dependent memories. fMRI activity for learning new virtual mazes which overlap with familiar routes was compared with activity for learning completely distinct routes. Results demonstrate both the hippocampus and caudate are preferentially recruited for learning mazes which overlap with existing route memories. Furthermore, both areas update their responses to familiar route memories which become context-dependent, suggesting complementary roles in both learning and updating overlapping representations. Together, these studies demonstrate that navigational decisions based on overlapping representations rely on a network incorporating hippocampal function with the evaluation and selection of behavior in the prefrontal cortex and striatum

A coordinate-based meta-analysis of music-evoked emotions

Since the publication of the first neuroscience study investigating emotion with music about two decades ago, the number of functional neuroimaging studies published on this topic has increased each year. This research interest is in part due to the ubiquity of music across cultures, and to music's power to evoke a diverse range of intensely felt emotions. To support a better understanding of the brain correlates of music-evoked emotions this article reports a coordinate-based meta-analysis of neuroimaging studies (n = 47 studies with n = 944 subjects). The studies employed a range of diverse experimental approaches (e.g., using music to evoke joy, sadness, fear, tension, frissons, surprise, unpleasantness, or feelings of beauty). The results of an activation likelihood estimation (ALE) indicate large clusters in a range of structures, including amygdala, anterior hippocampus, auditory cortex, and numerous structures of the reward network (ventral and dorsal striatum, anterior cingulate cortex, orbitofrontal cortex, secondary somatosensory cortex). The results underline the rewarding nature of music, the role of the auditory cortex as an emotional hub, and the role of the hippocampus in attachment-related emotions and social bonding.publishedVersio

Memory of my victory and your defeat: Contributions of reward- and memory-related regions to the encoding of winning events in competitions with others.

Social interactions enhance human memories, but little is known about how the neural mechanisms underlying episodic memories are modulated by rewarding outcomes in social interactions. To investigate this, fMRI data were recorded while healthy young adults encoded unfamiliar faces in either a competition or a control task. In the competition task, participants encoded opponents' faces in the rock-paper-scissors game, where trial-by-trial outcomes of Win, Draw, and Lose for participants were shown by facial expressions of opponents (Angry, Neutral, and Happy). In the control task, participants encoded faces by assessing facial expressions. After encoding, participants recognized faces previously learned. Behavioral data showed that emotional valence for opponents' Angry faces as the Win outcome was rated positively in the competition task, whereas the rating for Angry faces was rated negatively in the control task, and that Angry faces were remembered more accurately than Neutral or Happy faces in both tasks. fMRI data showed that activation in the medial orbitofrontal cortex (mOFC) paralleled the pattern of valence ratings, with greater activation for the Win than Draw or Lose conditions of the competition task, and the Angry condition of the control task. Moreover, functional connectivity between the mOFC and hippocampus was increased in Win compared to Angry, and the mOFC-hippocampus functional connectivity predicted individual differences in subsequent memory performance only in Win of the competition task, but not in any other conditions of the two tasks. These results demonstrate that the memory enhancement by context-dependent social rewards involves interactions between reward- and memory-related regions