Differential contributions of hippocampus and medial prefrontal cortex to self-projection and self-referential processing

Abstract

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.

The influence of the hippocampus and declarative memory on word use: Patients with amnesia use less imageable words

“…We restricted analyses to these 90 s descriptions of a specific moment of the (re)constructed event. In the original analysis of these data, Kurczek et al (2015) found that the patients with hippocampal amnesia produced narratives that contained significantly fewer episodic details, across all time periods, consistent with the literature (Race et al, 2011). Sessions were video- and audio-taped for analysis.…”

“…The current study is a reanalysis of data reported by Kurczek et al (2015). In that study, participants were given a neutral cue word (bird, clock, farm, garden, hotel, lake, radio, restaurant, river, snow, teacher, truck) and asked to produce 12 narratives, including three unique narratives of autobiographical events occurring in each of four time periods (Real Past, Imagined Past, Imagined Present, and Future).…”

“…To assess a potential relation between lexical properties of individual words and the number of episodic detail in the narratives we used the previously reported (Kurczek et al, 2015) coding of episodic and semantic content following the Autobiographical Interview (AI) scoring procedures outlined by Levine et al (2002). Consistent with established conventions, details were defined as unique occurrences, observations or thoughts, which each independently convey information, and each detail was classified as either internal or external.…”

“…The hippocampus and MTL have also been implicated in integration and retrieval of the perceptual details that constitute rich, vivid episodic memories across (e.g., Schacter and Addis, 2009; St-Laurent et al, 2014). Patients with hippocampal amnesia produce autobiographical narratives of past and future events that contain significantly fewer episodic details and that are described and rated as less vivid than those of healthy comparison participants (e.g., Hassabis et al, 2007; Kurczek et al, 2015; Race et al, 2011). …”

The imaginative mind

“…Interestingly, some evidence indicates that these may not be mutually exclusive hypotheses, and that varying functional roles may be differentially undertaken by distinct components of the same circuitry. For instance, Kurczek et al (2015) reported that compared to healthy matched control participants, neurological patients with lesions of the medial prefrontal cortex showed impairments in self-referential evaluation but not selfprojection, whereas patients with lesions of the medial temporal lobe showed the opposite pattern in that they were impaired in self-projection but not self-referential thinking (Kurczek et al, 2015).…”