Identification of the human medial temporal lobe regions on magnetic resonance images

et al. 2015

We evaluated two different perspectives about the function of the human hippocampus-one that emphasizes the importance of memory and another that emphasizes the importance of spatial processing and scene construction. We gave tests of boundary extension, scene construction, and memory to patients with lesions limited to the hippocampus or large lesions of the medial temporal lobe. The patients were intact on all of the spatial tasks and impaired on all of the memory tasks. We discuss earlier studies that associated performance on these spatial tasks to hippocampal function. Our results demonstrate the importance of medial temporal lobe structures for memory and raise doubts about the idea that these structures have a prominent role in spatial cognition.T wo traditions of work have influenced discussion about the function of the hippocampus (1). One tradition is based on work with memory-impaired patients and the idea that the hippocampus is important for a particular kind of memory (2, 3). The other tradition is based on work with rodents and the idea that the hippocampus is critical for spatial mapping (4). Its possible role in spatial processing has been recently explored in humans as well (5), and it has been proposed that the human hippocampus is essential for the ability to construct spatially coherent scenes (6, 7).This view of hippocampal function has depended on evidence from two kinds of tasks: boundary extension and scene construction (6,8). Boundary extension refers to the tendency to reconstruct a scene such that it has a larger background than was actually presented (9). In the Mullally et al. (8) study, memoryimpaired patients exhibited boundary extension less strongly than controls. Scene construction refers to the ability to imagine and describe spatially coherent scenes. In two studies, memoryimpaired patients made few references to space when visualizing and describing imagined scenes (6,8).It is unclear how to reconcile such findings with the view that the hippocampus chiefly supports memory functions. In particular, the idea that the construction and visualization of scenes involves the hippocampus seems at odds with the historic distinction between short-term (working) memory and long-term memory and the related idea that short-term memory is independent of the hippocampus (10-12). According to this perspective, hippocampal damage should not impair performance on spatial tasks, so long as testing puts no burden on long-term memory. In an attempt to clarify these issues, we gave tests of boundary extension, scene construction, and memory to patients with well-characterized lesions limited to the hippocampus or large lesions of the medial temporal lobe.Results Experiment 1. Both controls and hippocampal patients exhibited boundary extension. That is, both groups drew the central objects such that they occupied less area than in the original photographs ( Fig. 1 controls = 61.9% of the original area, hippocampal patients = 62.5% of the original area, P < 0.01). The extent of reduction was simil...

Section: Methodsmentioning

confidence: 97%

Memory, scene construction, and the human hippocampus

Kim

Dede

et al. 2015

“…The minus values indicate volumes that were larger for a patient than for controls. These values are based on published guidelines for identifying the boundaries of the parahippocampal gyrus (20,21).…”

Section: Methodsmentioning

confidence: 99%

Medial temporal lobe and topographical memory

Urgolites

Squire

2017

There has been interest in the idea that medial temporal lobe (MTL) structures might be especially important for spatial processing and spatial memory. We tested the proposal that the MTL has a specific role in topographical memory as assessed in tasks of scene memory where the viewpoint shifts from study to test. Building on materials used previously for such studies, we administered three different tasks in a total of nine conditions. Participants studied a scene depicting four hills of different shapes and sizes and made a choice among four test images. In the Rotation task, the correct choice depicted the study scene from a shifted perspective. MTL patients succeeded when the study and test images were presented together but failed the moment the study scene was removed (even at a 0-s delay). In the No-Rotation task, the correct choice was a duplicate of the study scene. Patients were impaired to the same extent in the No-Rotation and Rotation tasks after matching for difficulty. Thus, an inability to accommodate changes in viewpoint does not account for patient impairment. In the Nonspatial-Perceptual task, the correct choice depicted the same overall coloring as the study scene. Patients were intact at a 2-s delay but failed at longer, distraction-filled delays. The different results for the spatial and nonspatial tasks are discussed in terms of differences in demand on working memory. We suggest that the difficulty of the spatial tasks rests on the neocortex and on the limitations of working memory, not on the MTL.hippocampus | spatial memory | working memory | long-term memory T he capacity to form declarative memory depends on the integrity of the hippocampus and related medial temporal lobe (MTL) structures (1, 2). Declarative memory provides for the representation of relationships and permits comparison among items and contexts (3). There has also been interest in the idea that the MTL, and the hippocampus in particular, might have a special role in spatial processing beyond its established role in memory (4, 5). Several studies have reported that patients with damage to the MTL were impaired in various kinds of spatial tasks, even when the burden on memory appeared quite small and when tasks of nonspatial memory appeared less affected (6-9).In one series of studies, MTL patients were impaired when they needed to appreciate a rotation in viewpoint from one perspective to another (6, 10, 11). For example, participants studied a scene depicting four hills of different shapes and sizes placed at different locations in the scene. They then decided which of four test images depicted the same study scene but now rotated from 15 to 90 degrees (6). MTL patients performed worse than controls even when a brief delay (2 s) intervened between study and test.A question arises as to whether the impairment reflects a specific difficulty in appreciating the rotation of perspective, or whether an equally severe impairment would be found even if no rotation occurred. A second question is whether the impairment reflects...

“…The volume of the parahippocampal gyrus (including temporopolar, perirhinal, entorhinal, and parahippocampal cortices) is reduced by 11%, −5%, 12%, −17%, 10%, and −5% for K.E., R.S., J.R.W., L.J., G.W., and D.A., respectively (all values within 2 SDs of the control mean). These values are based on published guidelines for identifying the boundaries of the parahippocampal gyrus (29,30). The negative values indicate instances where the volume was larger for a patient than for controls.…”

Section: Methodsmentioning

confidence: 99%

Autobiographical memory, future imagining, and the medial temporal lobe

Dede

Wixted

et al. 2016

In two experiments, patients with damage to the medial temporal lobe (MTL) and healthy controls produced detailed autobiographical narratives as they remembered past events (recent and remote) and imagined future events (near and distant). All recent events occurred after the onset of memory impairment. The first experiment aimed to replicate the methods of Race et al.[Race E, Keane MM, Verfaellie M (2011) J Neurosci 31(28):10262-10269]. Transcripts from that study were kindly made available for independent analysis, which largely reproduced the findings from that study. Our patients produced marginally fewer episodic details than controls. Patients from the earlier study were more impaired than our patients. Patients in both groups had difficulty in returning to their narratives after going on tangents, suggesting that anterograde memory impairment may have interfered with narrative construction. In experiment 2, the experimenter used supportive questioning to help keep participants on task and reduce the burden on anterograde memory. This procedure increased the number of details produced by all participants and rescued the performance of our patients for the distant past. Neither of the two patient groups had any special difficulty in producing spatial details. The findings suggest that constructing narratives about the remote past and the future does not depend on MTL structures, except to the extent that anterograde amnesia affects performance. The results further suggest that different findings about the status of autobiographical memory likely depend on differences in the location and extent of brain damage in different patient groups.hippocampus | remote memory | anterograde amnesia E pisodic memory affords the capacity to recollect past events that occurred at a particular time and place (2). In humans, episodic recollection allows for reexperiencing an event through a process of "mental time travel" (3). The hippocampus is known to be important for episodic memory, but its specific contribution is unclear. In one view, the hippocampus is needed for the formation and consolidation of long-term memory for a limited time after learning (4). This view finds support in reports that patients with hippocampal damage were intact at recollecting episodes from early life (and impaired only for more recent time periods) (5-7). Another view holds that episodic memories remain dependent on the hippocampus so long as they persist (8, 9). In support of this idea, patients with hippocampal damage were sometimes impaired at recollecting events from early life (1, 10). A third view follows from the suggestion that the same process that enables recollection of the past is also engaged when imagining the future (11-15). In two studies, patients with hippocampal damage were impaired at imagining new experiences or future events (1, 14, but also see ref.6). This deficit has been proposed to be part of a broader impairment in the ability to construct spatially coherent scenes (15).The present study explored these divergent v...