Converging evidence points to a neural network that supports a range of abilities including remembering the past, thinking about the future, and introspecting about oneself and others. Neuroimaging studies find hippocampal activation during event construction tasks, and patients with hippocampal amnesia are impaired in their ability to (re)construct events of the past and the future. Neuroimaging studies of constructed experiences similarly implicate the medial prefrontal cortex (mPFC), but it remains unknown whether the mPFC is critical for such processes. The current study compares performance of five patients with bilateral mPFC damage, six patients with bilateral hippocampal damage, and demographically matched comparison participants on an event construction task. Participants were given a neutral cue word and asked to (re)construct events across four time conditions: real past, imagined past, imagined present, and future. These event narratives were analyzed for the number of internal and external details to quantify the extent of episodic (re)experiencing. Given the literature on the involvement of the mPFC in self-referential processing, we also analyzed the event narratives for self-references. The patients with mPFC damage did not differ from healthy comparison participants in their ability to construct highly detailed episodic events across time periods but displayed disruptions in their incorporation of the self. Patients with hippocampal damage showed the opposite pattern; they were impaired in their ability to construct highly detailed episodic events across time periods but not in their incorporation of the self. The results suggest differential contributions of hippocampus and medial prefrontal cortex to the distributed neural network for various forms of self-projection.
Creativity requires the rapid combination and recombination of existing mental representations to create novel ideas and ways of thinking. The hippocampal system, through its interaction with neocortical storage sites, provides a relational database necessary for the creation, updating, maintenance, and juxtaposition of mental representations used in service of declarative memory. Given this functionality, we hypothesized that hippocampus would play a critical role in creative thinking. We examined creative thinking, as measured by verbal and figural forms of the Torrance Tests of Creative Thinking (TTCT), in a group of participants with hippocampal damage and severe declarative memory impairment as well as in a group of demographically matched healthy comparison participants. The patients with bilateral hippocampal damage performed significantly worse than comparison participants on both the verbal and figural portions of the TTCT. These findings suggest that hippocampus plays a role critical in creative thinking, adding to a growing body of work pointing to the diverse ways the hallmark processing features of hippocampus serve a variety of behaviors that require flexible cognition.
A growing body of work suggests the hippocampus contributes to a variety of cognitive domains beyond its traditional role in memory. We propose that the hippocampus, in its capacity for relational binding, representational flexibility, and on-line maintenance and integration of multimodal relational representations, is a key contributor to language processing. Here we test the hypothesis that the on-line interpretation of pronouns is hippocampus-dependent. We combined eye-tracking with neuropsychological methods, where participants (4 patients with bilateral hippocampal damage and severe declarative memory impairment, 4 patients with ventromedial prefrontal cortex (vmPFC) damage, and healthy comparison participants) viewed a scene while listening to short dialogs introducing two characters; e.g., “Melissa” is playing violin for “Debbie”/”Danny” as the sun is shining overhead. She is wearing a blue/purple dress. Consistent with previous work, analysis of eye-gaze showed that younger and older healthy comparison participants and the vmPFC patients rapidly identified the intended referent of the pronoun when gender uniquely identified the referent, and when it did not, they showed a preference to interpret the pronoun as referring to the first-mentioned character. By contrast, hippocampal patients, while exhibiting a similar gender effect, exhibited significant disruptions in their ability to use information about which character had been mentioned first to interpret the pronoun. This finding suggests that the hippocampus plays a role in maintaining and integrating information even over a very short discourse history. These observed disruptions in referential processing demonstrate how promiscuously the hallmark processing features of the hippocampus are used in service of a variety of cognitive domains including language.
Background Discourse cohesion and coherence gives our communication continuity. Deficits in cohesion and coherence have been reported in patients with cognitive-communication disorders (e.g., TBI, dementia). However, the diffuse nature of pathology and widespread cognitive deficits of these disorders have made identification of specific neural substrates and cognitive systems critical for cohesion and coherence challenging. Aims Taking advantage of a rare patient group with selective and severe declarative memory impairments, the current study attempts to isolate the contribution of declarative memory to the successful use of cohesion and coherence in discourse. Methods & Procedures Cohesion and coherence were examined in the discourse of six participants with hippocampal amnesia and six demographically matched comparison participants. Specifically, this study (1) documents the frequency, type, and completeness of cohesive ties; (2) evaluates discourse for local and global coherence; and (3) compares use of cohesive ties and coherence ratings in amnesia and healthy participants. Outcomes & Results Overall, amnesia participants produced fewer cohesive ties per T-unit, the adequacy of their ties were more often judged to be incomplete, and the ratings of their local coherence were consistently lower than comparison participants. Conclusions These findings suggest that declarative memory may contribute to the discursive use of cohesion and coherence. Broader notions of cohesion, or interactional cohesion, i.e., cohesion across speakers (two or more people), time (days, weeks), and communicative resources (gesture), warrant further study as the experimental tasks used in the literature, and here, may actually underestimate or overestimate the extent of impairment.
Aging affects the ability to retrieve words for production, despite maintainence of lexical knowledge. In this study, we investigate the influence of lexical variables on picture naming accuracy and latency in adults ranging in age from 22 to 86 years. In particular, we explored the influence of phonological neighborhood density, which has been shown to exert competitive effects on word recognition, but to facilitate word production, a finding with implications for models of the lexicon. Naming responses were slower and less accurate for older participants, as expected. Target frequency also played a strong role, with facilitative frequency effects becoming stronger with age. Neighborhood density interacted with age, such that naming was slower for high-density than low-density items, but only for older subjects. Explaining this finding within an interactive activation model suggests that, as we age, the ability of activated neighbors to facilitate target production diminishes, while their activation puts them in competition with the target.
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