The medial temporal lobe supports conceptual implicit memory

Authors:

• Wei-Chun Wang

• Michele Lazzara

• Charan Ranganath

• Robert T. Knight

• Andrew P. Yonelinas

Date: 2010

DOI: 10.1016/j.neuron.2010.11.009

PubMed: 21144998

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Abstract:

The medial temporal lobe (MTL) is generally thought to be critical for explicit, but not implicit, memory. Here, we demonstrate that the perirhinal cortex (PRc), within the MTL, plays a role in conceptuallydriven implicit memory. Amnesic patients with MTL lesions that converged on the left PRc exhibited defi- cits on two conceptual implicit tasks (i.e., exemplar generation and semantic decision). A separate functional magnetic resonance imaging (fMRI) study in healthy subjects indicated that PRc activation during encoding of words was predictive of subsequent exemplar generation. Moreover, across subjects, the magnitude of the fMRI and behavioral conceptual priming effects were directly related. Additionally, the PRc region implicated in the fMRI study was the same region of maximal lesion overlap in the patients with impaired conceptual priming. These patient and imaging results converge to suggest that the PRc plays a critical role in conceptual implicit memory, and possibly conceptual processing in general.

Intact recollection memory in high-performing older adults: ERP and behavioral evidence

Authors:

• Audrey Duarte

• Charan Ranganath

• Celina Trujillo

• Robert T. Knight

Date: 2006

PubMed: 16417681

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Abstract:

Numerous behavioral studies have suggested that normal aging has deleterious effects on episodic memory and that recollection is disproportionately impaired relative to familiarity-based recognition. However, there is a wide degree of variability in memory performance within the aging population and this generalization may not apply to all elderly adults. Here we investigated these issues by using event-related potentials (ERPs) to measure the effects of aging on the neural correlates of recollection and familiarity in older adults with recognition memory performance that was equivalent to (old-high) or lower than (old-low) that of young adults. Results showed that, behaviorally, old-high subjects exhibited intact recollection but reduced familiarity, whereas old-low subjects had impairments in both recollection and familiarity, relative to the young. Consistent with behavioral results, old-high subjects exhibited ERP correlates of recollection that were topographically similar to those observed in young subjects. However, unlike the young adults, old-high subjects did not demonstrate any neural correlates of familiarity-based recognition. In contrast to the old-high group, the old-low group exhibited neural correlates of recollection that were topographically distinct from those of the young. Our results suggest that the effects of aging on the underlying brain processes related to recollection and familiarity are dependent on individual memory performance and highlight the importance of examining performance variability in normal aging.

Effects of unilateral prefrontal lesions on familiarity, recollection, and source memory

Authors:

• Audrey Duarte

• Charan Ranganath

• Robert T. Knight

Date: 2005

PubMed: 16148241

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Abstract:

Recognition memory can be supported by both the assessment of the familiarity of an item and by recollection of the context in which an item was encountered. Some have hypothesized that the prefrontal cortex (PFC) disproportionately contributes to recollection, whereas an alternative view is that the PFC contributes to both recollection and familiarity. Here, we examined the effects of prefrontal lesions on recollection and familiarity. Patients with unilateral PFC lesions and age-, gender-, and education-matched controls encoded pictures of meaningful objects that were presented briefly to the left or right visual field and subsequently performed recognition tests for centrally presented objects. Laterality effects within the PFC were also assessed in relation to recollection and familiarity processes. Patients with prefrontal lesions showed impaired familiarity-based recognition, and this deficit was specific for objects encoded by the lesioned hemisphere. In addition, recollection of the context in which each item was encountered was impaired independent of the visual field of presentation in patients with left prefrontal lesions. Recollection measured by subjective reports ("remember") was not impaired in either left or right frontal patients. These findings suggest that the PFC plays a critical role in recognition memory based on familiarity as well as recollection. Furthermore, these results suggest that left PFC regions are critical for source recollection.

Dissociable neural correlates for familiarity and recollection during the encoding and retrieval of pictures

Authors:

• Audrey Duarte

• Charan Ranganath

• Laurel Winward

• Dustin Hayward

• Robert T. Knight

Date: 2004

PubMed: 14741312

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Abstract:

Results from behavioral studies have supported the idea that recognition memory can be supported by at least two different processes, recollection and familiarity. However, it remains unclear whether these two forms of memory reflect neurally distinct processes. Furthermore, it is unclear whether recollection and familiarity can be best conceived as differing primarily in terms of retrieval processing, or whether they additionally differ at encoding. To address these issues, we used event-related brain potentials (ERPs) to monitor neural correlates of familiarity and recollection at both encoding and retrieval. Participants studied pictures of objects in two types of study blocks and subsequently made remember-know and source memory judgments during retrieval. Results showed that, during encoding, neural correlates of subsequent familiarity and recollection onsetted in parallel, but exhibited differences in scalp topography and time course. Subsequent familiarity-based recognition was associated with a left-lateralized enhanced positivity and observed at anterior scalp sites from 300 to 450 ms, whereas subsequent recollection was associated with a topographically distinct right-lateralized positivity at anterior scalp sites from 300 to 450 ms and bilateral activity from 450 to 600 ms. During retrieval, neural correlates of familiarity emerged earlier than correlates of recollection. Familiarity was associated with an enhanced positivity at frontopolar scalp sites from 150 to 450 ms, whereas recollection was associated with positive ERP modulations over bilateral frontal (300-600 ms) and parietal (450-800 ms) sites. These results demonstrate that familiarity and recollection reflect the outcome of neurally distinct memory processes at both encoding and retrieval.

Prefrontal cortex and episodic memory: integrating findings from neuropsychology and event-related neuroimaging.

ABSTRACT

Although it has been speculated for many years that the prefrontal cortex plays a role in long-term memory for events, or episodic memory, only recently have researchers made a concerted attempt to define this role. Most theories of prefrontal function suggest that this region implements “topdown” or “executive” processes that influence a variety of domains, including memory. For example, Luria (1966) postulated a role for the frontal lobes in the regulation of voluntary attention and the organisation of goal-directed behavior. Building on the work of Luria, Shallice (1982) argued that the frontal lobes are required for the attentional selection of schemes of action in novel situations. A complementary role suggested for the prefrontal cortex is the suppression of irrelevant or interfering stimuli (Brutkowski, 1965; Fuster, 1997; Knight, Staines, Swick, & Chao, 1999; Pribram, Ahumada, Hartog, & Roos, 1964; Shimamura, 1995). Teuber (1964) additionally proposed that the frontal lobes prepare sensory areas for environmental changes that will be induced by motor actions. This concept was later extended to include the generation of anticipatory behavioural sets (Fuster, 1997; Nauta, 1971). Several researchers have also postulated a central role for the prefrontal cortex in active, or working memory (Fuster, 1997; Goldman-Rakic, 1987).

AUTHORS

• Charan Ranganath

• Robert T. Knight

Date: 2003

ISBN-13: 978-1841692463

ISBN-10: 9781841692463

Prefrontal cortex and episodic memory: integrating findings from neuropsychology and functional brain imaging

Authors:

• Charan Ranganath

• Robert T. Knight

Date: 2003

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