Extent of hippocampal atrophy predicts degree of deficit in recall

Abstract

Which specific memory functions are dependent on the hippocampus is still debated. The availability of a large cohort of patients who had sustained relatively selective hippocampal damage early in life enabled us to determine which type of mnemonic deficit showed a correlation with extent of hippocampal injury. We assessed our patient cohort on a test that provides measures of recognition and recall that are equated for difficulty and found that the patients' performance on the recall tests correlated significantly with their hippocampal volumes, whereas their performance on the equally difficult recognition tests did not and, indeed, was largely unaffected regardless of extent of hippocampal atrophy. The results provide new evidence in favor of the view that the hippocampus is essential for recall but not for recognition.long-standing issue in memory research is the identity of the mnemonic process served by each of the components of the medial temporal lobe (MTL). Recall, which is the ability to retrieve from memory a stimulus or its context that is no longer present, is a more complex function than recognition, which is the ability to identify a current stimulus as old or new, or to choose a previously encountered stimulus among competing distractors. Over the years, a large number of studies have been conducted, aiming to tease apart the relative contribution of different MTL structures to recall and recognition. Many investigators have proposed that these two distinct memory processes rely on different MTL structures, with recall being dependent on the hippocampus and recognition being supported by parahippocampal structures, such as the perirhinal and entorhinal cortices (1-5, but see ref. 6). Also, studies examining the effects of damage to the mammillary bodies and fornices, structures within the hippocampal circuit, have shown that volume loss is correlated with deficits in recall but not in recognition (7,8).However, there is also evidence suggesting that both processes rely on the hippocampus (for a review, see ref. 6). Most of the literature on either side of this controversy is composed of studies with single cases or small sample sizes. Indeed, to date, none of the studies involving humans has been able to demonstrate a clear relationship between memory process and hippocampal volume (HV), possibly due to lack of variability in HV loss. Additionally, many of the contradictory findings could result from measures used to test recognition and recall not being equated for level of difficulty.Previous work from our group demonstrated that patients with developmental amnesia due to severe hippocampal pathology sustained early in life are seriously impaired in their ability to recall visual or verbal stimuli but are relatively unimpaired in recognizing them (9). By identifying a group of patients with varying extents of HV reduction, and applying a standardized measure of memory [the Doors and People test (D&P test) (10)] in which the recognition and recall subtests are matched for difficulty, we were abl...

Multiple determinants of lifespan memory differences

“…Indeed, we found that hippocampal GMV made a unique, positive contribution to the M1 factor. This is consistent with the hypothesized role of hippocampus in associative memory24, despite mixed findings in prior attempts to associate memory scores with structural brain measures606162 (though see refs 63 and 64). However, any simple dependence of M2 on anterior parahippocampus (as expected from prior association of perirhinal cortex with familiarity65), was not supported; nor was any simple dependence of M3 on fusiform (as expected from prior association of this region with visual priming66).…”

Hippocampal and diencephalic pathology in developmental amnesia

“…Whereas we failed to find a correlation between hippocampal volumes and the patients' memory performance in the current study, we had previously shown that such a relationship exists in a larger sample of patients with a history of neonatal hypoxia-ischaemia, whose hippocampal volumes ranged from severely reduced to normal (Cooper et al., 2015; see also; Patai et al., 2015). These results are not necessarily inconsistent.…”

“…Volumetric measurements of the hippocampus were carried out by one of the authors (DGG) (Gadian et al., 2000, Patai et al., 2015) using MEDx 3.43 (Medical Numerics, Inc., MD, USA). Detailed information on the procedures that were used for pre-processing of images, including identifying and outlining the boundaries of the hippocampus, is contained in Cooper et al.…”

A Guide to Designing a Memory fMRI Paradigm for Pre-surgical Evaluation in Temporal Lobe Epilepsy

“…Recall refers to the ability to bring back to mind consolidated representations and relies on recollection processes. Based on evidence from patients with bilateral hippocampal damage of early onset, it is recognized that the hippocampus supports recall processes (56). Recall-based memory should be considered in memory fMRI studies to represent ecological scenarios of everyday memory process, and to optimize hippocampal activation.…”