Accelerated forgetting in healthy older samples: Implications for methodology, future ageing studies, and early identification of risk of dementia

Accelerated long-term forgetting (ALF) has been reported in healthy older individuals, and is a possible early marker for risk of developing Alzheimer’s disease (AD). The Verbal Associative Learning & Memory Test (VALMT; McGibbon & Jansari, 2013) addresses methodological weaknesses in existing clinical tests and has detected ALF in epilepsy within an hour. We used VALMT to investigate learning and forgetting in healthy older participants. Older (60-69yrs) and Younger (19-31yrs) participants were compared. Using VALMT, unrelated word-pairs were learnt to criterion, then cued-recall tested at delays of 5, 30 and 55 minutes. Unique pairs were tested at each delay. Subjective memory complaints data was gathered, and the Wechsler Memory Scale Logical Memory test (WMS-LM; a standard clinical measure) was administered. VALMT identified a significant difference in delayed recall between Younger and Older groups by 55 minutes (d = 1.32). While ‘fast-learning’ Older participants scored similarly to Younger participants, ‘slow-learning’ Older participants were impaired at all delays. Forgetting rates suggested degradation of memory starts during early synaptic consolidation rather than later system-level consolidation. Increased subjective memory complaints were associated with reduced VALMT scores. By contrast, WMS-LM failed to identify significant differences between any groups, and did not correlate with memory complaints. We conclude VALMT may be better able than WMS-LM to identify subtle impairments in healthy older adults within a single clinical visit, and VALMT results better reflect subjective experience. Older slow-learners forget faster and report more subjective memory complaints, which may indicate a group at risk of developing AD

When “long-term memory” no longer means “forever”: analysis of accelerated long-term forgetting in a patient with temporal lobe epilepsy

Classical amnesia involves a difficulty in transferring information to long-term memory and can be detected with standard clinical tests. However, there are some patients who pass these tests but nonetheless show longer-term memory impairments. A case study is presented of a patient, RY, with temporal lobe epilepsy, who exhibited such a profile of “accelerated long-term forgetting”. To investigate the effect of recalling information on later retention, recall and recognition for pairs of novel stories were tested at five intervals ranging from 30 min to 4 weeks; we also manipulated whether or not recall and recognition were repeatedly tested for stories. Two studies are reported, one before RY commenced treatment with anticonvulsant medication, and one following 6 months of treatment. Very similar memory profiles were observed in both settings. Against a background of above average cognitive function, results showed that RY's free recall, although initially average or above, was significantly impaired at extended delays (within 24 h) for non-repeatedly recalled episodic information. However, this contrasted with normal performance for information that had been repeatedly recalled. An unresolved issue in the field is the impact of anticonvulsant medication on alleviating long-term forgetting, and the current study shows that anticonvulsant medication can have negligible beneficial effects in improving the rate of long-term forgetting in this type of patient. In addition, our study highlights the possible protective effect of active review of recent episodic memories

Detecting the onset of accelerated long-term forgetting: evidence from temporal lobe epilepsy

Accelerated long-term forgetting (ALF) refers to a slowly developing anterograde amnesia in which material is retained normally over short delays but then forgotten at an abnormally fast rate over days to weeks. Such long-term memory impairment is not detected by standard clinical tests. This study analysed ALF in a temporal lobe epileptic, RY. Key issues addressed were: (i) the timeframe of ALF onset; (ii) whether disruption of memory consolidation during sleep is a necessary requirement for precipitating ALF; (iii) the effectiveness of repeated recall in limiting the impact of ALF. RY's memory for novel word-pairings was compared with that of matched controls using cued-recall and forced choice recognition (FCR) tests at multiple delays (5, 30, 55, 240 min). To investigate the impact of repeated recall some pairings were recalled at all intervals, and all material (repeatedly and non-repeatedly recalled) was tested again after a 24 h delay. RY's initial learning and performance at 30 min were normal, but by 55 min both his cued-recall performance and the subjective quality of his recognition memory were significantly impaired. This suggests disruption of secondary consolidation processes occurring relatively soon after learning. It also raises the possibility of developing a standard test to diagnose ALF within a single clinical session rather than requiring multiple visits. Since RY remained awake it appears that disruption of memory consolidation during sleep is not a necessary condition for him to experience ALF. Repeated recall at multiple time-points within the first 4 h sustained normal recall performance to 24 h, indicating repeated recall could form the basis for a protective strategy

Accelerated Long-Term Forgetting: Development of a sensitive measure and its application to unanswered questions in forgetting research.

Accelerated Long-term Forgetting (ALF) is a disorder in which new information can be learnt and retained normally over short delays, but is then forgotten at an accelerated rate at longer delays. It was first detected in epilepsy, but has since been reported in healthy older individuals, and is a possible early marker for risk of developing Alzheimer’s disease (AD). Research has been hampered by lack of a methodologically sound test with adequate sensitivity which can be used in both research and clinical settings. In the current research a novel measure, the Verbal Associative Learning and Memory Test (VALMT), was developed from an initial face-to-face test into a fully automated online test, with parameters tuned to maximise sensitivity and avoid ceiling effects. In parallel, a novel set of practical guidelines were developed to assist in experimental design to ensure ceiling effects do not influence results. VALMT was used to investigate three topics: ALF symptoms in healthy ageing and the possibility of using ALF as a marker for those at risk of developing AD; memory performance over extended delays in the general population; the timeframe of onset of accelerated forgetting. This research showed that VALMT provides a sensitive measure of accelerated forgetting that can be used for all ages from 16 to 82, and is more sensitive than a standard clinical test (Wechsler Memory Scale Logical Memory). Testing across the lifespan indicated a gradual decline in memory performance starting in the 57-69 age band. Importantly, this research also highlighted the existence of a subset of healthy older participants who learn more slowly and forget more rapidly, and indicates the potential for this learning deficit and subsequent forgetting to be used to identify older individuals who are at risk of developing dementia, which will be of significant benefit in research and clinical practice

Detecting the onset of accelerated long-term forgetting: evidence from temporal lobe epilepsy

Accelerated long-term forgetting (ALF) refers to a slowly developing anterograde amnesia in which material is retained normally over short delays but then forgotten at an abnormally fast rate over days to weeks. Such long-term memory impairment is not detected by standard clinical tests. This study analysed ALF in a temporal lobe epileptic, RY. Key issues addressed were: (i) the timeframe of ALF onset; (ii) whether disruption of memory consolidation during sleep is a necessary requirement for precipitating ALF; (iii) the effectiveness of repeated recall in limiting the impact of ALF. RY's memory for novel word-pairings was compared with that of matched controls using cued-recall and forced choice recognition (FCR) tests at multiple delays (5, 30, 55, 240 min). To investigate the impact of repeated recall some pairings were recalled at all intervals, and all material (repeatedly and non-repeatedly recalled) was tested again after a 24 h delay. RY's initial learning and performance at 30 min were normal, but by 55 min both his cued-recall performance and the subjective quality of his recognition memory were significantly impaired. This suggests disruption of secondary consolidation processes occurring relatively soon after learning. It also raises the possibility of developing a standard test to diagnose ALF within a single clinical session rather than requiring multiple visits. Since RY remained awake it appears that disruption of memory consolidation during sleep is not a necessary condition for him to experience ALF. Repeated recall at multiple time-points within the first 4 h sustained normal recall performance to 24 h, indicating repeated recall could form the basis for a protective strategy

When "long-term memory" no longer means "forever": analysis of accelerated long-term forgetting in a patient with temporal lobe epilepsy

Classical amnesia involves a difficulty in transferring information to long-term memory and can be detected with standard clinical tests. However, there are some patients who pass these tests but nonetheless show longer-term memory impairments. A case study is presented of a patient, RY, with temporal lobe epilepsy, who exhibited such a profile of "accelerated long-term forgetting". To investigate the effect of recalling information on later retention, recall and recognition for pairs of novel stories were tested at five intervals ranging from 30 min to 4 weeks; we also manipulated whether or not recall and recognition were repeatedly tested for stories. Two studies are reported, one before RY commenced treatment with anticonvulsant medication, and one following 6 months of treatment. Very similar memory profiles were observed in both settings. Against a background of above average cognitive function, results showed that RY's free recall, although initially average or above, was significantly impaired at extended delays (within 24h) for non-repeatedly recalled episodic information. However, this contrasted with normal performance for information that had been repeatedly recalled. An unresolved issue in the field is the impact of anticonvulsant medication on alleviating long-term forgetting, and the current study shows that anticonvulsant medication can have negligible beneficial effects in improving the rate of long-term forgetting in this type of patient. In addition, our study highlights the possible protective effect of active review of recent episodic memories