Jason P. Mitchell

Multiple routes to memory: Distinct medial temporal lobe processes build item and source memories

A central function of memory is to permit an organism to distinguish between stimuli that have been previously encountered and those that are novel. Although the medial temporal lobe (which includes the hippocampus and surrounding perirhinal, parahippocampal, and entorhinal cortices) is known to be crucial for recognition memory, controversy remains regarding how the specific subregions within the medial temporal lobe contribute to recognition. We used event-related functional MRI to examine the relation between activation in distinct medial temporal lobe subregions during memory formation and the ability (i) to later recognize an item as previously encountered (item recognition) and (ii) to later recollect specific contextual details about the prior encounter (source recollection). Encoding activation in hippocampus and in posterior parahippocampal cortex predicted later source recollection, but was uncorrelated with item recognition. In contrast, encoding activation in perirhinal cortex predicted later item recognition, but not subsequent source recollection. These outcomes suggest that the subregions within the medial temporal lobe subserve distinct, but complementary, learning mechanisms.

The Link between Social Cognition and Self-referential Thought in the Medial Prefrontal Cortex

The medial prefrontal cortex (mPFC) has been implicated in seemingly disparate cognitive functions, such as understanding the minds of other people and processing information about the self. This functional overlap would be expected if humans use their own experiences to infer the mental states of others, a basic postulate of simulation theory. Neural activity was measured while participants attended to either the mental or physical aspects of a series of other people. To permit a test of simulation theorys prediction that inferences based on self-reflection should only be made for similar others, targets were subsequently rated for their degree of similarity to self. Parametric analyses revealed a region of the ventral mPFCpreviously implicated in self-referencing tasksin which activity correlated with perceived self/other similarity, but only for mentalizing trials. These results suggest that self-reflection may be used to infer the mental states of others when they are sufficiently similar to self.

Distinct neural systems subserve person and object knowledge

Studies using functional neuroimaging and patient populations have demonstrated that distinct brain regions subserve semantic knowledge for different classes of inanimate objects (e.g., tools, musical instruments, and houses). What this work has yet to consider, however, is how conceptual knowledge about people may be organized in the brain. In particular, is there a distinct functional neuroanatomy associated with person knowledge? By using event-related functional magnetic resonance imaging (fMRI), we measured neural activity while participants made semantic judgments about people or objects. A unique pattern of brain activity was associated with person judgments and included brain regions previously implicated in other aspects of social-cognitive functioning: medial prefrontal cortex, superior temporal cortex, intraparietal sulcus, and fusiform gyrus. These regions were generally marked by relatively little change from baseline brain activity for person judgments along with significant deactivations for object judgments. Together, these findings support the notion that person knowledge may be functionally dissociable from other classes of semantic knowledge within the brain.

The Seven Sins of Memory

Abstract: We examine the relation between memory and self by considering errors of memory. We draw on the idea that memorys imperfections can be classified into seven basic categories or “sins.” Three of the sins concern different types of forgetting (transience, absent‐mindedness, and blocking), three concern different types of distortion (misattribution, suggestibility, and bias), and one concerns intrusive memories (persistence). We focus in particular on two of the distortion‐related sins, misattribution and bias. By describing cognitive, neuropsychological, and neuroimaging studies that illuminate these memory sins, we consider how they might bear on the relation between memory and self.

Contextual Variations in Implicit Evaluation

In the present research, the authors examined contextual variations in automatic attitudes. Using 2 measures of automatic attitudes, the authors demonstrated that evaluative responses differ qualitatively as perceivers focus on different aspects of a targets social group membership (e.g., race or gender). Contextual variations in automatic attitudes were obtained when the manipulation involved overt categorization (Experiments 1-3) as well as more subtle contextual cues, such as category distinctiveness (Experiments 4-5). Furthermore, participants were shown to be unable to predict such contextual influences on automatic attitudes (Experiment 3). Taken together, these experiments support the idea of automatic attitudes being continuous, online constructions that are inherently flexible and contextually appropriate, despite being outside conscious control.

Encoding-Specific Effects of Social Cognition on the Neural Correlates of Subsequent Memory

To examine whether social cognition recruits distinct mental operations, we measured brain activity during social (“form an impression of this person”) and relatively nonsocial (“remember the order in which person information is presented”) orienting tasks. Extending previous research on the neural basis of social cognition, the impression formation task differentially engaged an extensive region of the dorsomedial prefrontal cortex (PFC). In contrast, the nonsocial sequencing task differentially engaged the superior frontal and parietal gyri, precentral gyrus, and the caudate. In addition, we compared encoding activations for subsequently remembered (i.e., hits) to subsequently forgotten (i.e., misses) items. The brain regions in which the blood oxygenation level-dependent signal distinguished subsequent hits from subsequent misses depended on which orienting task was performed at encoding: subsequent memory was correlated with encoding activity only in the medial PFC for impression formation trials but in the right hippocampus for sequencing trials. These data inform two interrelated cognitive issues. First, results underscore the neuroanatomical distinctiveness of social cognition and suggest that previous psychological theories may have neglected important functional differences in how the human brain instantiates social and nonsocial cognitive processes. Second, by demonstrating that activity in different brain regions correlates with subsequent memory as a function of the orienting task performed at encoding, these data provide evidence of the neural basis for encoding specificity, the principle that memory is critically determined by the cognitive process engaged by the initial study episode.

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.

General and specific contributions of the medial prefrontal cortex to knowledge about mental states

Recent neuroimaging research (Mitchell, J.P., Heatherton, T.F., Macrae, C.N., 2002. Distinct neural systems subserve person and object knowledge. Proc. Natl. Acad. Sci. U. S. A. 99, 15238-15243.) has suggested that semantic knowledge about the psychological aspects of other people draws on a pattern of neural activity that differentiates social from nonsocial semantics. Although the medial prefrontal cortex (mPFC) clearly plays a central role in a range of such social-cognitive tasks, little is known about the precise contributions made by this region to social semantics. The current study addressed two outstanding questions regarding mPFC function. First, do mPFC contributions to processing words that refer to psychological states extend to other, nonhuman targets or are they specific to understanding the psychological experience of conspecifics? Second, does the mPFC respond generally to tasks that require processing another person, or is its activity specific to understanding psychological characteristics? To address these questions, participants were scanned using fMRI while judging the applicability of words to one of two types of targets: people or dogs. For each target, participants made one of two types of semantic judgment: does this word describe a potential psychological state of the target or does this word refer to a physical part of the target? Results demonstrated that greater mPFC activation accompanied judgments of psychological states than of body parts regardless of whether the target was a person or a dog, indicating that mPFC contributions to social semantics are specific for understanding psychological states--directly countering recent suggestions that mPFC responds generally to any judgment about another person--and that mPFC activity extends to targets other than conspecifics.

Social Influence Modulates the Neural Computation of Value

Social influence—individuals’ tendency to conform to the beliefs and attitudes of others—has interested psychologists for decades. However, it has traditionally been difficult to distinguish true modification of attitudes from mere public compliance with social norms; this study addressed this challenge using functional neuroimaging. Participants rated the attractiveness of faces and subsequently learned how their peers ostensibly rated each face. Participants were then scanned using functional MRI while they rated each face a second time. The second ratings were influenced by social norms: Participants changed their ratings to conform to those of their peers. This social influence was accompanied by modulated engagement of two brain regions associated with coding subjective value—the nucleus accumbens and orbitofrontal cortex—a finding suggesting that exposure to social norms affected participants’ neural representations of value assigned to stimuli. These findings document the utility of neuroimaging to demonstrate the private acceptance of social norms.

Social psychology as a natural kind

Although typically defined as the study of how people and groups interact, the field of social psychology comprises several disparate domains that make only indirect contributions to understanding interpersonal interaction, such as emotion, attitudes and the self. Although these various phenomena seem to have little in common, recent evidence indicates that the topics at the core of social psychology form a natural group of domains with a common functional neuroanatomy, centered on the medial prefrontal cortex. That self-referential, attitudinal, affective and other social phenomena converge on this region might reflect their shared reliance on inexact and internally generated estimates that differ from the more precise representations underlying other psychological phenomena.