A critical role of the human hippocampus in an electrophysiological measure of implicit memory (original) (raw)

Brain responses of explicit and implicit memory - an ERP study

2006

Implicit memory is acquired by an unintentional or unconscious learning. Recognition memory involves either automatic knowing or consciously controlled remembering. We provided an eventrelated potential paradigm capable of di¡erentiating memory for the explicitly learned, implicitly learned and unstudied materials. In the explicit memory, we obtained both frontal (controlled retrieval) and parietal (recollection) old/new e¡ects. In the implicit memory, we found persistent occipitotemporal activation (visual priming) and late attenuation in the temporoparietooccipital (repetition suppression). Event-related potential provides an insight into the dissociable mechanism of memory function that supports the dual process model with an enhanced temporal resolution on the dynamic process of both explicit perceptual learning and implicit perceptual priming. NeuroReport 17:1483^1486 c 2006 Lippincott Williams & Wilkins.

Brain responses of explicit and implicit memory: an event-related potential study

NeuroReport, 2006

Neurophysiological evidence for a recollection impairment in amnesia patients that leaves familiarity intact

Neuropsychologia, 2012

In several previous behavioral studies, we have identified a group of amnestic patients that, behaviorally, appear to exhibit severe deficits in recollection with relative preservation of familiarity-based recognition. However, these studies have relied exclusively on behavioral measures, rather than direct measures of physiology. Event-related potentials (ERPs) have been used to identify putative neural correlates of familiarity- and recollection-based recognition memory, but little work has been done to determine the extent to which these ERP correlates are spared in patients with relatively specific memory disorders. ERP studies of recognition in healthy subjects have indicated that recollection and familiarity are related to a parietal old-new effect characterized as a late positive component (LPC) and an earlier mid-frontal old-new effect referred to as an ‘FN400’, respectively. Here, we sought to determine the extent to which the putative ERP correlates of recollection and familiarity are intact or impaired in these patients. We recorded ERPs in three amnestic patients and six age matched controls while they made item recognition and source recognition judgments. The current patients were able to discriminate between old and new items fairly well, but showed nearly chance-level performance at source recognition. Moreover, whereas control subjects exhibited ERP correlates of memory that have been linked to recollection and familiarity, the patients only exhibited the mid-frontal FN400 ERP effect related to familiarity-based recognition. The results show that recollection can be severely impaired in amnesia even when familiarity-related processing is relatively spared, and they also provide further evidence that ERPs can be used to distinguish between neural correlates of familiarity and recollection.► The memory processes impaired in mild amnesia patients has been contentiously debated. ► Neuropsychological dissociations using behavioral measures have been inconclusive. ► ERPs provide neurophysiological signals of recollection (LPC) and familiarity (FN400). ► We recorded ERPs of item and source memory in mild amnesia and healthy controls. ► Patients showed FN400 correlates of familiarity, but no LPC evidence of recollection.

Microscopy Research and Technique, 2000

As event-related brain potential (ERP) researchers have increased the number of recording sites, they have gained further insights into the electrical activity in the neural networks underlying explicit memory. A review of the results of such ERP mapping studies suggests that there is good correspondence between ERP results and those from brain imaging studies that map hemodynamic changes. This concordance is important because the combination of the high temporal resolution of ERPs with the high spatial resolution of hemodynamic imaging methods will provide a greatly increased understanding of the spatio-temporal dynamics of the brain networks that encode and retrieve explicit memories.

Journal of Experimental Psychology: Learning, Memory, and Cognition, 1997

Explicit memory declines with age while implicit memory remains largely intact. These experiments extended behavioral findings by recording event-related potentials (ERPs) in young and elderly adults during repetition priming and recognition memory paradigms. Words and pronounceable nonwords repeated after 1 of 3 delays. Stimuli were categorized as either word-nonword or old-new. Repeated items elicited more positive-going potentials in bom tasks. Hemispheric asymmetries for word and nonword processing were observed during lexical decision: Repetition effects were larger over the left hemisphere for words and over the right hemisphere for nonwords. For the young, ERP repetition effects were larger during recognition memory. For old adults, conversely, repetition produced more positive-going waveforms during lexical decision. The elderly had ERP and behavioral deficits at long recognition delays. ERP repetition effects in the elderly, like behavioral performance, were preserved in an implicit task but impaired in an explicit memory task. Neuropsychological studies of amnesic patients have facilitated the classification of memory into different subsystems (see Polster, Nadel, & Schacter, 1991; Squire, Knowlton, & Musen, 1993; T\ilving, 1983, for reviews). Explicit memory is exemplified by an ability to overtly recall some event or recognize a particular stimulus presented in the past, whereas implicit memory does not require deliberate recollection but involves a change in test performance resulting from prior exposure to specific information (Schacter, Chiu, & Ochsner, 1993; Tulving & Schacter, 1990). Although patients with severe anterograde amnesia are unable to recall or recognize material presented only a few minutes ago (Milner, 1965), they may show behavioral evidence that the same information influences performance on a variety of tasks tapping implicit memory (Cermak,

Dissecting out conscious and unconscious memory (sub)processes within the human medial temporal lobe

NeuroImage, 2003

The human medial temporal lobe (MTL) system mediates memories that can be consciously recollected. However, the specific natures of the individual contributions of its various subregions to conscious memory processes remain equivocal. Here we show a functional dissociation between the hippocampus proper and the parahippocampal region in conscious and unconscious memory as revealed by invasive recordings of limbic event-related brain potentials recorded during explicit and implicit word recognition: Only hippocampal and not parahippocampal neural activity exhibits a sensitivity to the implicit versus explicit nature of the recognition memory task. Moreover, only within the hippocampus proper do the neural responses to repeated words differ not only from those to new words but also from each other as a function of recognition success. By contrast parahippocampal (rhinal) responses are sensitive to repetition independent of conscious recognition. These findings thus demonstrate that it is the hippocampus proper among the MTL structures that is specifically engaged during conscious memory processes.

Brain research. Cognitive brain research, 2001

This study investigates event related potentials (ERP) elicited by true and false recognition using words from different semantic categories. In Experiment 1, ERPs for true and false recognition were more positive than for correctly rejected NEW words starting around 300 ms after test word presentation (old/new ERP effects). ERP waveforms for true and false recognition revealed equal early (300-500 ms) fronto-medial old/new ERP effects, reflecting similar familiarity processes, but smaller parietal old/new ERP effects (500-700 ms) for false relative to true recognition, suggesting less active recollection. Interestingly, a subsequent performance based group comparison showed equivalent old/new ERP effects for true and false recognition for participants with high rates of false recognition. In contrast, false recognition failed to elicit an old/new ERP effect in a group with low false recognition rates. To examine whether this between group difference was driven by the differential u...

Temporal lobe epilepsy as a model to understand human memory: The distinction between explicit and implicit memory

Epilepsy & Behavior, 2006

Decades of research have provided substantial evidence of memory impairments in patients with temporal lobe epilepsy (TLE), including deficits in the encoding, storage, and retrieval of new information. These findings are not surprising, given the associated underlying neuroanatomy, including the hippocampus and surrounding medial temporal lobe structures. Because of its associated anatomic and cognitive characteristics, TLE has provided an excellent model by which to examine specific aspects of human memory functioning, including classic distinctions such as that between explicit and implicit memory. Various clinical and experimental research studies have supported the idea that both conscious and unconscious processes support memory functioning, but the role of relevant brain structures has been the subject of debate. This review is concerned with a discussion of the current status of this research and, importantly, how TLE can inform future studies of memory distinctions.

Neuropsychology, 1997

The proposition that cortically based perceptual representation systems (PRSs) are responsible for some implicit priming phenomena was examined by using event-related potentials (ERPs) in repetition and masked word priming. Experiment 1 used an explicit recognition task, in which repeated words replicated previous ERP repetition priming effects, whereas masked repetition priming revealed a new ERP effect with a posterior topography. Experiment 2 demonstrated ERP and behavioral priming in a lexical decision task for repetition and masked repetition priming. Topographical mapping of ERP repetition priming effects involved both early and late effects over the right and left anterior regions, whereas masked priming produced only an early ERP effect posteriorly. These results suggest differences between early and late ERP priming effects in terms of explicit recollection. Moreover, a posterior PRS may not be involved in some longer term implicit repetition priming effects.

Implicit memory within a word recognition task: an event-related potential study in human subjects

Neuroscience Letters, 1999

First, we recorded brain potentials from 15 healthy young subjects during the performance of a word/non-word discrimination task. During continuous visual presentation, some of the meaningful words were repeated after 86±94 s. We found a signi®cant decrease of response time associated with the classi®cation of repeated words which is an index for priming, an unconscious brain process. However, event-related potentials (ERPs) did not differ signi®cantly between ®rst and second presentations. Second, we recorded brain potentials during a following recognition test. Some of the meaningful words which were presented only once during the semantic discrimination task were repeated and had to be discriminated from randomly interspersed new words. We compared ERPs produced by incorrectly classi®ed repeated words (misses) with ERPs produced by correctly classi®ed new words (correct rejections). We found early ERP differences between 250 and 400 ms and later differences starting at about 500 ms after the stimulus onset. The early effect occurred over parietal scalp locations and the later effect over frontal, parietal and occipital scalp locations. This is evidence for unconscious brain activity related to the processing of missed repeated words. We suggest that the later frontal effect we found is due to an enhanced effort of the retrieval of item representations during word recognition and that the earlier parietal effect re¯ects partial recognition. q

A critical role of the human hippocampus in an electrophysiological measure of implicit memory (original) (raw)

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