Overdependence on degraded gist memory in Alzheimer's disease.

Abstract

Alzheimer's disease (AD) reduces associative effects on false recognition in the Deese-Roediger-McDermott task, either due to impaired memory for gist or impaired use of gist in memory decisions. Gist processes were manipulated by blocking or mixing studied words according to their associations and by varying the associative strength between studied and nonstudied words at test. Both associative blocking and associative strength had smaller effects on false recognition in AD patients than in control participants, consistent with gist memory impairments. However, unlike the case with control participants, blocking influenced true and false recognition equally in AD patients, demonstrating an overdependence on gist when making memory decisions. AD also impaired item-specific recollections, relative to control participants, as true recognition of studied words was reduced even when the two groups were equated on gist-based false recognition. We propose that the overdependence on degraded gist memory in AD is caused by even larger impairments in item-specific recollections.

The effects of healthy aging, amnestic mild cognitive impairment, and Alzheimer's disease on recollection, familiarity and false recognition, estimated by an associative process-dissociation recognition procedure

“…However, false recognition clearly decreases with cognitive impairment (whether understood as aMCI or as AD), supporting the idea that these patients also have less gist memory (e.g. Budson et al, 2006a;Gallo et al, 2006;Hudon et al, 2006), which coincides with their familiarity deficits, described above. For this reason, it seems reasonable to suppose that a significant decline in false recognition in older people could be considered another early marker of cognitive impairment (e.g.…”

“…Hildebrant et al, 2009aHildebrant et al, , 2009b because it would indicate a significant deficit in their gist memory. The fact that young people and AD patients do not differ on their false recognition rates is probably due to two different causes: as we mentioned above, young people show a low rate of false recognition because they correctly use the recall-to-reject strategy to reduce their false alarm rates, while the AD patients show low false recognition rates because they show an overdependence on their impaired gist memory (Gallo et al, 2006;Hudon et al, 2006). For these two different reasons, stimulus repetition does not affect the young people or the AD patients, but it does increase false recognition in healthy older people and aMCI patients.…”

“…However, several other studies have shown that false recognition is significantly lower in aMCI and AD patients than in healthy older adults (but only after controlling for the basal level of false alarms; e.g. Budson et al, 2000;Hudon et al, 2006), which has been interpreted to mean that the gist memory of these patients is diminished (Budson et al, 2000(Budson et al, , 2006aGallo et al, 2006;Hudon et al, 2006). However, if we do not control the basal level of false alarms, these patients can show false recognition rates that are similar to or greater than those found in healthy people of the same age (e.g.…”

False Recognition Helps to Distinguish Patients with Alzheimer’s Disease and Amnestic MCI from Patients with Other Kinds of Dementia

“…A second, less generally accepted explanation states that false recognitions and intrusions are direct consequences of the memory impairment. Because memory performance is impaired, patients accept familiar information as valid targets and this leads to an increased number of false recognitions [17,18] . Recently, we developed a third explanation for the high number of false recognitions in AD patients.…”

“…The usual interpretation of this finding is that the memory deficit prevents the semantic relations (the 'gist') to become stored too, and therefore the number of false recognitions of semantically related lures is not increased (at least after single trial presentations) [17,18] . Just as in the case of prioritem intrusions, it has been argued that the more liberal response bias -that is, the increase of false recognitions irrespective of the study context -may be a consequence of a deficit in inhibition, and therefore, from a frontal lobe dysfunction [13] .…”