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The hippocampus is generally considered to have relatively late involvement in recognition memory, its main electrophysiological signature being between 400 and 800 ms after stimulus onset. However, most electrophysiological studies have analyzed the hippocampus as a single responsive area, selecting only a single-site signal exhibiting the strongest effect in terms of amplitude. These classical approaches may not capture all the dynamics of this structure, hindering the contribution of other hippocampal sources that are not located in the vicinity of the selected site. We combined intracerebral electroencephalogram recordings from epileptic patients with independent component analysis during a recognition memory task involving the recognition of old and new images. We identified two sources with different responses emerging from the hippocampus: a fast one (maximal amplitude at ∼250 ms) that could not be directly identified from raw recordings and a latter one, peaking at ∼400 ms. The former component presented different amplitudes between old and new items in 6 out of 10 patients. The latter component had different delays for each condition, with a faster activation (∼290 ms after stimulus onset) for recognized items. We hypothesize that both sources represent two steps of hippocampal recognition memory, the faster reflecting the input from other structures and the latter the hippocampal internal processing. Recognized images evoking early activations would facilitate neural computation in the hippocampus, accelerating memory retrieval of complementary information. Overall, our results suggest that the hippocampal activity is composed of several sources with an early activation related to recognition memory., Competing Interests: The authors declare no competing financial interests., (Copyright © 2024 López-Madrona et al.)

One key item of information retrieved when surveying our visual world is whether or not objects are familiar. However, there is no consensus on the respective roles of medial temporal lobe structures, particularly the perirhinal cortex (PRC) and hippocampus. We considered whether the PRC could support a fast recognition memory system independently from the hippocampus. We recorded the intracerebral electroencephalograph activity of epileptic patients while they were performing a fast visual recognition memory task, constraining them to use their quickest strategy. We performed event-related potential (ERP) and classification analyses. The PRC was, by far, the earliest region involved in recognition memory. This activity occurred before the first behavioral responses and was found to be related to reaction times, unlike the hippocampus. Single-trial analyses showed that decoding power was equivalent in the PRC and hippocampus but occurred much earlier in the PRC. A critical finding was that recognition memory-related activity occurred in different frontal and parietal regions, including the supplementary motor area, before the hippocampus. These results, based on ERP analyses, suggest that the human brain is equipped with a fast recognition memory system, which may bypass the hippocampus and in which the PRC plays a critical role., (© The Author(s) 2019. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

In 2006 Mitchell demonstrated that implicit memory was robust to decay. He showed that the ability to identify fragments of pictures seen 17 years before was significantly higher than for new stimuli. Is this true only for implicit memory? In this study, we tested whether explicit memory was still possible for drawings (n = 144) that had been presented once or three times, two seconds each time on average, approximately 12 years earlier. Surprisingly, our data reveal that our participants were able to recognize pictures above chance level. Preserved memory was mainly observed in the youngest subjects, for stimuli seen three times. Despite the fact that confidence judgments were low, reports suggest that recognition could be based on a strong sense of familiarity. These data extend Mitchell's findings and show that familiarity can also be robust to decay., (Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.)

Although it is known that medial temporal lobe (MTL) structures support declarative memory, the fact these structures have different architectonics and circuitry suggests they may also play different functional roles. Selective lesions of MTL structures offer an opportunity to understand these roles. We report, in this study, on JMG, a patient who presents highly unusual lesions that completely affected all MTL structures except for the right hippocampus and parts of neighbouring medial parahippocampal cortex. We first demonstrate that JMG shows preserved recall for visual material on 5 experimental tasks. This finding suggests that his right hippocampus is functional, even though it appears largely disconnected from most of its MTL afferents. In contrast, JMG performed very poorly, as compared to control subjects, on 7 tasks of visual recognition memory for single items. Although he sometimes performed above chance, neither familiarity nor recollection appeared fully preserved. These results indicate that extrahippocampal structures, damaged bilaterally in JMG, perform critical operations for item recognition; and that the hippocampus cannot take over that role, including recollection, when these structures are largely damaged. Finally, in a set of 3 recognition memory tasks with scenes as stimuli, JMG performed at the level of control participants and obtained normal indices of familiarity and recollection. Overall, our findings suggest that the right hippocampus and remnants of parahippocampal cortex can support recognition memory for scenes in the absence of preserved item-recognition memory. The patterns of dissociations, which we report in the present study, provide support for a representational account of the functional organization of MTL structures., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Models of recognition memory have postulated that the mammillo-thalamic tract (MTT)/anterior thalamic nucleus (AN) complex would be critical for recollection while the Mediodorsal nucleus (MD) of the thalamus would support familiarity and indirectly also be involved in recollection (Aggleton et al., 2011). 12 patients with left thalamic stroke underwent a neuropsychological assessment, three verbal recognition memory tasks assessing familiarity and recollection each using different procedures and a high-resolution structural MRI. Patients showed poor recollection on all three tasks. In contrast, familiarity was spared in each task. No patient had significant AN lesions. Critically, a subset of 5 patients had lesions of the MD without lesions of the MTT. They also showed impaired recollection but preserved familiarity. Recollection is therefore impaired following MD damage, but familiarity is not. This suggests that models of familiarity, which assign a critical role to the MD, should be reappraised.

Objective: Episodic memory impairment is at the core of amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD). The origin of memory deficits may result either from an encoding deficit or from an accelerated decline of the memory trace. The present study explores these two hypotheses., Method: We used the delayed-matching-to sample 48 items (DMS-48) memory test in a group of controls, aMCI patients, and AD patients (n= 16 in each group). The DMS-48 offers an incidental learning phase followed by three forced-choice recognition tests at three-minute, one-hour, and one-week delays. Moreover, the forced-choice test distinguishes three kinds of couple items: abstract (meaningless), paired (two similar exemplars), and unique (two different objects) items., Results: As predicted by the accelerated forgetting hypothesis, patients showed a decrease in recognition performance over time. Controls also exhibited a similar decline in performance. As predicted by the encoding deficit hypothesis, abstract items were the most poorly recognized in AD, at both the three-minute and the one-week delays. In AD, recognition of the paired items also dropped after the one-hour delay, followed by unique items after a one-week delay. Patients with aMCI exhibited a performance that was similar to controls, except for abstract items, which dropped at the one-week delay., Conclusions: These results are discussed in light of a third hypothesis, the memory strength hypothesis, in order to better account for the progressive decline in memory performance as a function of the item type in AD.

Recognition memory--affected early in the course of Alzheimer Disease (AD)--is supposed to rely on two processes: recollection (i.e., retrieval of details from the encoding episode) and familiarity (i.e., acontextual sense of prior exposure). Recollection has repeatedly been shown to be impaired in patients with amnestic Mild Cognitive Impairment (aMCI)--known to be at high risk for AD. However, studies that evaluated familiarity in these patients have reported conflicting results. Here, we assessed familiarity in single-domain aMCI patients (n = 19) and healthy matched controls (n = 22). All participants underwent a classic yes/no recognition memory paradigm with confidence judgements, allowing an estimation of familiarity and recollection similar to the approach used in previous studies. In addition, they underwent a novel speeded recognition memory task, the Speed and Accuracy Boosting procedure, based on the idea that familiarity is fast and hence that fast answers rely on familiarity. On the classic yes/no task, aMCI patients were found to have impaired performance, reaction times, recollection and familiarity. However, performance and reaction times of aMCI patients did not differ from that of controls in the speeded task. This is noteworthy since this task was comparatively difficult for control subjects. This dissociation within familiarity suggests that a very basic component of declarative memory, probably at the interface between implicit and explicit memory, may be preserved, or possibly released, in patients with aMCI. It is suggested that early subprocesses (e.g., fluency based familiarity) could be preserved in aMCI patients, while delayed ones (e.g., conceptual fluency, post-retrieval monitoring, confidence assessment, or even access to awareness) may be impaired. These findings may provide support for recent suggestions that familiarity may result from the combination of a set of subprocesses, each with its specific temporal signature., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Background: In the common form of Alzheimer's disease (AD), neurofibrillary tangles, which are associated with cognitive dysfunction, initially develop in the anterior subhippocampal (perirhinal/entorhinal) cortex before reaching the hippocampus. This area plays a key role in visual recognition memory (VRM). Impaired VRM could therefore be an early marker of AD., Methods: An extensive neuropsychological assessment including VRM tasks was performed in 26 patients with single-domain amnestic mild cognitive impairment at baseline. We evaluated the diagnostic accuracy of neuropsychological tests using ROC curve analyses in a prospective longitudinal study until conversion to probable AD or with a follow-up of at least 6 years., Results: VRM performance predicted conversion to AD with a sensitivity of 80% and a specificity of 90.9%. Combining the assessment of VRM with a verbal memory task increased diagnostic accuracy., Conclusions: Cognitive 'biomarkers' evaluating the function of brain areas that are the target of degenerative change should be considered for the early diagnosis of AD., (Copyright © 2013 S. Karger AG, Basel.)

Purpose: Performance in recognition memory differs among patients with medial temporal lobe epilepsy (MTLE). We aimed to determine if distinct recognition performances (normal vs. impaired) could be related to distinct patterns of brain activation during encoding., Methods: Event-related functional magnetic resonance imaging (fMRI) activation profiles were obtained during successful encoding of non-material-specific items, in 14 MTLE patients tested for recognition of stimuli afterward. Findings were compared to those of 25 healthy subjects, and voxel-based correlations were assessed between brain activation and performance., Key Findings: Patients with left and right MTLE showed similar activations and similar performances. As a whole, the group of patients demonstrated altered recognition scores, but three of the seven patients with left MTLE and three of the seven patients with right MTLE exhibited normal performance relative to controls. In comparison to healthy subjects and patients with impaired recognition, patients with normal recognition showed weaker activations in left opercular cortex, but stronger activations in bilateral parahippocampal region/fusiform gyrus (PH/FG). By contrast, patients with impaired performance showed weaker activations in bilateral PH/FG, but stronger activations in a frontal/cingulate and parietal network. Recognition performance was correlated positively to bilateral PH/FG activations, and negatively correlated to bilateral frontal/cingulate activations, in the whole group of patients, as well as in subgroups of patients with either left or right MTLE., Significance: These results suggest occurrence of effective functional compensation within bilateral PH/FG in MTLE, allowing patients to maintain recognition capability. In contrast, impairment of this perceptive-memory system may lead to alternative activation of an inefficient nonspecific attentional network in patients with altered performance., (Wiley Periodicals, Inc. © 2011 International League Against Epilepsy.)

Through study of clinical cases with brain lesions as well as neuroimaging studies of cognitive processing of words and pictures, it has been established that material-specific hemispheric specialization exists. It remains however unclear whether such specialization holds true for all processes involved in complex tasks, such as recognition memory. To investigate neural signatures of transition from perception to recognition, according to type of material (words or abstract pictures), high-resolution scalp ERPs were recorded in adult humans engaged either in categorization or in memory recognition tasks within the same experimental setup. Several steps in the process from perception to recognition were identified. Source localization showed that the early stage of perception processing (N170) takes place in the fusiform gyrus and is lateralized according to the nature of stimuli (left side for words and right side for pictures). Late stages of processing (N400/P600) corresponding to recognition are material independent and involve anterior medial-temporal and ventral prefrontal structures bilaterally. A crucial transitional process between perception (N170) and recognition (N400/P600) is reflected by the N270, an often overlooked component, which occurs in anterior rhinal cortices and shows material-specific hemispheric lateralization.

We encounter many faces each day but relatively few are personally familiar. Once faces are familiar, they evoke semantic and social information known about the person. Neuroimaging studies demonstrate differential brain activity to familiar and non-familiar faces; however, brain responses related to personally familiar faces have been more rarely studied. We examined brain activity with fMRI in adults in response to faces of their mothers and fathers compared to faces of celebrities and strangers. Overall, faces of mothers elicited more activity in core and extended brain regions associated with face processing, compared to fathers, celebrity or stranger faces. Fathers' faces elicited activity in the caudate, a deep brain structure associated with feelings of love. These new findings of differential brain responses elicited by faces of mothers and fathers are consistent with psychological research on attachment, evident even during adulthood., (2010 Elsevier Inc. All rights reserved.)

Investigations of the neural correlates of face recognition have typically used old/new paradigms where subjects learn to recognize new faces or identify famous faces. Familiar faces, however, include one's own face, partner's and parents' faces. Using event-related fMRI, we examined the neural correlates of these personally familiar faces. Ten participants were presented with photographs of own, partner, parents, famous and unfamiliar faces and responded to a distinct target. Whole brain, two regions of interest (fusiform gyrus and cingulate gyrus), and multiple linear regression analyses were conducted. Compared with baseline, all familiar faces activated the fusiform gyrus; own faces also activated occipital regions and the precuneus; partner faces activated similar areas, but in addition, the parahippocampal gyrus, middle superior temporal gyri and middle frontal gyrus. Compared with unfamiliar faces, only personally familiar faces activated the cingulate gyrus and the extent of activation varied with face category. Partner faces also activated the insula, amygdala and thalamus. Regions of interest analyses and laterality indices showed anatomical distinctions of processing the personally familiar faces within the fusiform and cingulate gyri. Famous faces were right lateralized whereas personally familiar faces, particularly partner and own faces, elicited bilateral activations. Regression analyses show experiential predictors modulated with neural activity related to own and partner faces. Thus, personally familiar faces activated the core visual areas and extended frontal regions, related to semantic and person knowledge and the extent and areas of activation varied with face type., (Copyright 2009 Wiley-Liss, Inc)

There is ongoing debate about whether performance on tests of recognition memory can remain preserved after hippocampal damage. In the present study, we report F.R.G., a patient who became severely amnesic following herpes simplex encephalitis. Although F.R.G. failed all tests involving recall and verbal recognition, she obtained normal performance on a wide number of tests evaluating visual recognition memory (14 of 18 different tests). Her performance was independent of various factors, such as test difficulty, duration of exposure to the stimuli, or delay separating encoding and recognition. F.R.G. also achieved normal performance on two tasks requiring that she associate pairs of visual stimuli. In addition, she demonstrated spared feeling of knowing, suggesting that her performance on recognition tests was explicit and likely to rely on familiarity. Brain imaging (MRI) revealed bilateral lesions of the hippocampus and lesions of the left parahippocampal gyrus, while the right parahippocampal gyrus remained relatively spared. The results of this study support the view that recognition memory can be preserved despite severe hippocampal damage and that familiarity is a distinct memory process that can be dissociated from recollection., (Copyright 2005 Wiley-Liss, Inc.)