Brandon A. Ally

Episodic simulation of future events is impaired in mild Alzheimer's disease

Recent neuroimaging studies have demonstrated that both remembering the past and simulating the future activate a core neural network including the medial temporal lobes. Regions of this network, in particular the medial temporal lobes, are prime sites for amyloid deposition and are structurally and functionally compromised in Alzheimers disease (AD). While we know some functions of this core network, specifically episodic autobiographical memory, are impaired in AD, no study has examined whether future episodic simulation is similarly impaired. We tested the ability of sixteen AD patients and sixteen age-matched controls to generate past and future autobiographical events using an adapted version of the Autobiographical Interview. Participants also generated five remote autobiographical memories from across the lifespan. Event transcriptions were segmented into distinct details, classified as either internal (episodic) or external (non-episodic). AD patients exhibited deficits in both remembering past events and simulating future events, generating fewer internal and external episodic details than healthy older controls. The internal and external detail scores were strongly correlated across past and future events, providing further evidence of the close linkages between the mental representations of past and future.

Music as a Memory Enhancer in Patients with Alzheimer’s Disease

Musical mnemonics have a long and diverse history of popular use. In addition, music processing in general is often considered spared by the neurodegenerative effects of Alzheimers disease (AD). Research examining these two phenomena is limited, and no work to our knowledge has explored the effectiveness of musical mnemonics in AD. The present study sought to investigate the effect of music at encoding on the subsequent recognition of associated verbal information. Lyrics of unfamiliar childrens songs were presented bimodally at encoding, and visual stimuli were accompanied by either a sung or a spoken recording. Patients with AD demonstrated better recognition accuracy for the sung lyrics than the spoken lyrics, while healthy older adults showed no significant difference between the two conditions. We propose two possible explanations for these findings: first, that the brain areas subserving music processing may be preferentially spared by AD, allowing a more holistic encoding that facilitates recognition, and second, that music heightens arousal in patients with AD, allowing better attention and improved memory.

Is the parietal lobe necessary for recollection in humans

An intriguing puzzle in cognitive neuroscience over recent years has been the common observation of parietal lobe activation in functional neuroimaging studies during the performance of human memory tasks. These findings have surprised scientists and clinicians because they challenge decades of established thinking that the parietal lobe does not support memory function. However, direct empirical investigation of whether circumscribed parietal lobe lesions might indeed be associated with human memory impairment has been lacking. Here we confirm using functional magnetic resonance imaging that significant parietal lobe activation is observed in healthy volunteers during a task assessing recollection of the context in which events previously occurred. However, patients with parietal lobe lesions that overlap closely with the regions activated in the healthy volunteers nevertheless exhibit normal performance on the same recollection task. Thus, although the processes subserved by the human parietal lobe appear to be recruited to support memory function, they are not a necessary requirement for accurate remembering to occur.

Parietal contributions to recollection: Electrophysiological evidence from aging and patients with parietal lesions

There has been much recent investigation into the role of parietal cortex in memory retrieval. Proposed hypotheses include attention to internal memorial representations, an episodic working memory-type buffer, and an accumulator of retrieved memorial information. The current investigation used event-related potentials (ERPs) to test the episodic buffer hypothesis, and to assess the memorial contribution of parietal cortex in younger and older adults, and in patients with circumscribed lateral parietal lesions. In a standard recognition memory paradigm, subjects studied color pictures of common objects. One-third of the test items were presented in the same viewpoint as the study phase, one-third were presented in a 90 degrees rotated viewpoint, and one-third were presented in a noncanonical viewpoint. Conflicting with the episodic buffer hypothesis, results revealed that the duration of the parietal old/new effect was longest for the canonical condition and shortest for the noncanonical condition. Results also revealed that older adults demonstrated a diminished parietal old/new effect relative to younger adults. Consistent with previous data reported by Simons et al., patients with lateral parietal lesions showed no behavioral impairment compared to controls. Behavioral and ERP data from parietal lesion patients are presented and discussed. From these results, the authors speculate that the parietal old/new effect may be the neural correlate of an individuals subjective recollective experience.

An evaluation of recollection and familiarity in Alzheimer’s disease and mild cognitive impairment using receiver operating characteristics

There is a need to investigate exactly how memory breaks down in the course of Alzheimers disease (AD). Examining what aspects of memorial processing remain relatively intact early in the disease process will allow us to develop behavioral interventions and possible drug therapies focused on these intact processes. Several recent studies have worked to understand the processes of recollection and familiarity in patients with mild cognitive impairment (MCI) and very mild AD. Although there is general agreement that these patient groups are relatively unable to use recollection to support veridical recognition decisions, there has been some question as to how well these patients can use familiarity. The current study used receiver operating characteristic (ROC) curves and a depth of processing manipulation to understand the effect of MCI and AD on the estimates of recollection and familiarity. Results showed that patients with MCI and AD were impaired in both recollection and familiarity, regardless of the depth of encoding. These results are discussed in relation to disease pathology and in the context of recent conflicting evidence as to whether familiarity remains intact in patients with MCI. The authors highlight differences in stimuli type and task difficulty as possibly modulating the ability of these patients to successfully use familiarity in support of memorial decisions.

The worth of pictures: using high density event-related potentials to understand the memorial power of pictures and the dynamics of recognition memory.

To understand the neural correlates of the memorial power of pictures, pictures and words were systematically varied at study and test within subjects, and high-density event-related potentials (ERPs) were recorded at retrieval. Using both conventional and novel methods, the results were presented as ERP waveforms, 50 ms scalp topographies, and video clips, and analyzed using t-statistic topographic maps and nonparametric p-value maps. The authors found that a parietally-based ERP component was enhanced when pictures were presented at study or test, compared to when words were presented. An early frontally-based component was enhanced when words were presented at study compared to pictures. From these data the authors speculate that the memorial power of pictures is related to the ability of pictures to enhance recollection. Familiarity, by contrast, was enhanced when words were presented at study compared to pictures. From these results and the dynamic view of memory afforded by viewing the data as video clips, the authors propose an ERP model of recognition memory.

Aging memory for pictures : Using high-density event-related potentials to understand the effect of aging on the picture superiority effect

High-density event-related potentials (ERPs) were used to understand the effect of aging on the neural correlates of the picture superiority effect. Pictures and words were systematically varied at study and test while ERPs were recorded at retrieval. Here, the results of the word-word and picture-picture study-test conditions are presented. Behavioral results showed that older adults demonstrated the picture superiority effect to a greater extent than younger adults. The ERP data helped to explain these findings. The early frontal effect, parietal effect, and late frontal effect were all indistinguishable between older and younger adults for pictures. In contrast, for words, the early frontal and parietal effects were significantly diminished for the older adults compared to the younger adults. These two old/new effects have been linked to familiarity and recollection, respectively, and the authors speculate that these processes are impaired for word-based memory in the course of healthy aging. The findings of this study suggest that pictures allow older adults to compensate for their impaired memorial processes, and may allow these memorial components to function more effectively in older adults.

The picture superiority effect in patients with Alzheimer’s disease and mild cognitive impairment

The fact that pictures are better remembered than words has been reported in the literature for over 30 years. While this picture superiority effect has been consistently found in healthy young and older adults, no study has directly evaluated the presence of the effect in patients with Alzheimers disease (AD) or mild cognitive impairment (MCI). Clinical observations have indicated that pictures enhance memory in these patients, suggesting that the picture superiority effect may be intact. However, several studies have reported visual processing impairments in AD and MCI patients which might diminish the picture superiority effect. Using a recognition memory paradigm, we tested memory for pictures versus words in these patients. The results showed that the picture superiority effect is intact, and that these patients showed a similar benefit to healthy controls from studying pictures compared to words. The findings are discussed in terms of visual processing and possible clinical importance.

Preserved frontal memorial processing for pictures in patients with mild cognitive impairment.

Amnestic mild cognitive impairment (aMCI) has been conceptualized as a transitional stage between healthy aging and Alzheimers disease (AD). Therefore, understanding which aspects of memory are impaired and which remain relatively intact in these patients can be useful in determining who will ultimately go on to develop AD, and subsequently designing interventions to help patients live more engaged and independent lives. The dual-process model posits that recognition memory decisions can rely on either familiarity or recollection. Whereas research is fairly consistent in showing impaired recollection in patients with aMCI, the results have been mixed regarding familiarity. A noted difference between these studies investigating familiarity has been stimulus type. The goal of the current investigation was to use high-density event-related potentials (ERPs) to help elucidate the neural correlates of recognition decisions in patients with aMCI for words and pictures. We also hoped to help answer the question of whether patients can rely on familiarity to support successful recognition. Patients and controls participated in separate recognition memory tests of words and pictures while ERPs were recorded during retrieval. Results showed that ERP components typically associated with familiarity and retrieval monitoring were similar between groups for pictures. However, these components were diminished in the patient group for words. Based on recent work, the authors discuss the possibility that implicit conceptual priming could have contributed to the enhanced ERP correlate of familiarity. Further, the authors address the possibility that enhanced retrieval monitoring may be needed to modulate increased familiarity engendered by pictures.

Pattern separation and pattern completion in Alzheimer's disease: Evidence of rapid forgetting in amnestic mild cognitive impairment

Over the past four decades, the characterization of memory loss associated with Alzheimers disease (AD) has been extensively debated. Recent iterations have focused on disordered encoding versus rapid forgetting. To address this issue, we used a behavioral pattern separation task to assess the ability of the hippocampus to create and maintain distinct and orthogonalized visual memory representations in patients with amnestic mild cognitive impairment (aMCI) and mild AD. We specifically used a lag‐based continuous recognition paradigm to determine whether patients with aMCI and mild AD fail to encode visual memory representations or whether these patients properly encode representations that are rapidly forgotten. Consistent with the rapid forgetting hypothesis of AD, we found that patients with aMCI demonstrated decreasing pattern separation rates as the lag of interfering objects increased. In contrast, patients with AD demonstrated consistently poor pattern separation rates across three increasingly longer lags. We propose a continuum that reflects underlying hippocampal neuropathology whereby patients with aMCI are able to properly encode information into memory but rapidly lose these memory representations, and patients with AD, who have extensive hippocampal and parahippocampal damage, cannot properly encode information in distinct, orthogonal representations. Our results also revealed that whereas patients with aMCI demonstrated similar behavioral pattern completion rates to healthy older adults, patients with AD showed lower pattern completion rates when we corrected for response bias. Finally, these behavioral pattern separation and pattern completion results are discussed in terms of the dual process model of recognition memory.