Use of explicit memory cues in patients with amnestic mild cognitive impairment
Kleber, Kara Teresa
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Along with impaired memory, Alzheimer’s disease (AD) patients having amnestic mild cognitive impairment (aMCI) show a high rate of false memory distortions. The impact of these events on the lives of AD patients warrants further research into their neurobiological mechanisms. One type of distortion, known as false recognition, results in a greater tendency to endorse unstudied items as “old” on recognition memory tests. This tendency means patients often response “old” more than 50% of the time and is known as liberal response bias. Originally thought to be a byproduct of poor discrimination, evidence now demonstrates it to be part of a distinct neurological process (Budson et al. 2006). Further understanding of the processes responsible for determining individuals’ responses will help researchers understand the origin of false recognition and have the potential to direct effective behavioral interventions for patients and caregivers. Studies aiming to attribute these finding to abnormalities in the frontal lobes have been inconclusive. Parietal lobe activity has been associated with recognition memory in many studies over a variety of paradigms, including work examining shifting the decision criteria, responsible for altering response bias. Differences in how AD patients with aMCI set criteria for recognition could be important in understanding their high rate of false recognitions. Recently, patients with parietal lesions have been shown to use explicit memory cues differently than healthy controls, suggesting that the parietal lobes may function in integrating external information when setting decision criteria. Our objective was to determine whether patients with aMCI would show results similar to those seen in parietal patients, due to the early AD-related pathophysiologic involvement of the parietal lobes in aMCI patients. Ten aMCI patients and 10 healthy controls were administered a recognition memory test that incorporated a mix of correct (valid) and incorrect (invalid) cues presented before the stimuli in the test phase. Participants were instructed that the test would include some trials preceded with hints of 80% accuracy. Patients and controls completed two recognition memory tests, one utilizing a shallow encoding at study and one using a deep encoding. We compared the baseline performance (performance with no cue) to cued performance in order to determine if the two groups used the cued condition in different ways. If AD damages processes within the parietal lobe required for utilizing information to set decision criteria, then patients with AD would not be affected negatively by invalid “Likely New” cues, and their performance would not improve on validly cued new item trials. Significant differences were seen between groups for the use of “Likely Old” cues in one condition (shallow). While statistically significant interaction effects were not observed for other conditions, graphical representations of data suggest future study is needed to reject or accept our hypothesis.
Thesis (M.A.)--Boston University