Mind-wandering in people with hippocampal damage

Abstract

Acknowledgments:We thank all the participants, particularly the patients and their relatives, for the time and effort they contributed to this study. We also thank the consultant neurologists: Drs. M.J. Johnson, S.R. Irani, S. Jacobs and P. Maddison. We are grateful to Martina F. Callaghan for help with MRI sequence design, Trevor Chong for second scoring the Autobiographical Interview, Alice Liefgreen for second scoring the mind-wandering thoughts, and Elaine Williams for advice on hippocampal segmentation. E.A.M. and C.M. are supported by a Wellcome Principal Research Fellowship to E.A.M. (Abstract Subjective inner experiences, such as mind-wandering, represent the fundaments of human cognition. Although the precise function of mind-wandering is still debated, it is increasingly acknowledged to have influence across cognition on processes such as future planning, creative thinking and problem-solving, and even on depressive rumination and other mental health disorders. Recently, there has been important progress in characterizing mindwandering and identifying the associated neural networks. Two prominent features of mindwandering are mental time travel and visuo-spatial imagery, which are often linked with the hippocampus. People with selective bilateral hippocampal damage cannot vividly recall events from their past, envision their future or imagine fictitious scenes. This raises the question of whether the hippocampus plays a causal role in mind-wandering and if so, in what way. Leveraging a unique opportunity to shadow people (all males) with bilateralhippocampal damage for several days, we examined, for the first time, what they thought about spontaneously, without direct task demands. We found that they engaged in as much mind-wandering as control participants. However, whereas controls thought about the past, present and future, imagining vivid visual scenes, hippocampal damage resulted in thoughts primarily about the present comprising verbally-mediated semantic knowledge. These findings expose the hippocampus as a key pillar in the neural architecture of mind-wandering and also reveal its impact beyond memory, placing it at the heart of human mental life. Significance statementHumans tend to mind-wander about 30-50% of their waking time. Two prominent features of this pervasive form of thought are mental time travel and visuo-spatial imagery, which are often associated with the hippocampus. To examine whether the hippocampus plays a causal role in mind-wandering, we examined the frequency and phenomenology of mind-wandering 3 in patients with selective bilateral hippocampal damage. We found that they engaged in as much mind-wandering as controls. However, hippocampal damage changed the form and content of mind-wandering from flexible, episodic, and scene-based to abstract, semanticized, and verbal. These findings expose the hippocampus as a key pillar in the neural architecture of mind-wandering and reveal its impact beyond memory, placing it at the heart of our mental life.

A review of hippocampal activation in post‐traumatic stress disorder

“…Among the various ICNs, an important network of regions that are active at rest—default mode network (DMN)—has been identified and linked to mind wandering and self‐directed thought (Greicius, Krasnow, Reiss, & Menon, ). The hippocampus has been identified as a central node in the DMN, consistent with reports implicating the hippocampus in mind wandering, which often occurs during resting state assessment and involves episodic memory, visuospatial imagery, and mental time travel (McCormick et al, ). A number of studies have examined connectivity within the DMN and between the DMN and other networks, to investigate functional connectivity in PTSD using a seed‐based whole brain analysis.…”

“…A literature search was performed in PubMed, PsycINFO, and Web of Science databases. Search terms were chosen based on previously studied functions of the hippocampus and behavioral deficits in PTSD (Eichenbaum, ; Janak & Tye, ; McCormick, Rosenthal, Miller, & Maguire, ; Opitz, ; Sierra‐Mercado, Padilla‐Coreano, & Quirk, ). As structural differences have been addressed more extensively in the literature (Chao, Weiner, & Neylan, ; Childress et al, ; Logue et al, ; Nelson & Tumpap ), this review focused solely on hippocampal function.…”

The neural correlates of “mind blanking”: When the mind goes away

“…We investigated the neural correlates of MB, during which people's minds simply “disappear.” This state is independent from other mental states such as focusing and MW (Ward & Wegner, ), although its occurrence is not very frequent, ranging in previous studies from a few instances to 18% of total mental state (McCormick et al, ; Schooler et al, ; Ward & Wegner, ). However, the behavioral data from the current study suggest that the state of MB can be produced intentionally (Figure ).…”

“…During this state of mind blanking (MB), the individual is not focally aware of internal or external stimuli. Several previous works indicate that people often spontaneously describe their minds as being “blank” in a free‐response format (McCormick, Rosenthal, Miller, & Maguire, ; Schooler, Reichle, & Halpern, ; Watts & Sharrock, ). Although several experiments have indicated that MB is an independent psychological state, it remains difficult to detect.…”

Hippocampal atrophy and intrinsic brain network dysfunction relate to alterations in mind wandering in neurodegeneration

“…Dementia syndromes afford a unique opportunity to study the impact of network level dysfunction on mind wandering, given well-established pathology primarily targeting, but not restricted to, nodes of the default and frontoparietal networks (14,15). This approach is an extension to recent work confirming that focal lesions to the default network in the hippocampus and medial prefrontal cortex can impact the content of mind wandering or reduce its frequency (16,17). Moreover, on the cognitive level, many of the component processes implicated in mind wandering are disrupted in neurodegenerative disorders, for example, autobiographical memory retrieval (18,19), mental construction (20,21), working memory, and shifting attention (22,23).…”