Search

Visual search is an aspect of visual cognition that may be more impaired in Dementia with Lewy Bodies (DLB) than Alzheimer's disease (AD). To assess this possibility, the present study compared patients with DLB (n = 17), AD (n = 30), or Parkinson's disease with dementia (PDD; n = 10) to non-demented patients with PD (n = 18) and normal control (NC) participants (n = 13) on single-feature and feature-conjunction visual search tasks. In the single-feature task participants had to determine if a target stimulus (i.e., a black dot) was present among 3, 6, or 12 distractor stimuli (i.e., white dots) that differed in one salient feature. In the feature-conjunction task participants had to determine if a target stimulus (i.e., a black circle) was present among 3, 6, or 12 distractor stimuli (i.e., white dots and black squares) that shared either of the target's salient features. Results showed that target detection time in the single-feature task was not influenced by the number of distractors (i.e., "pop-out" effect) for any of the groups. In contrast, target detection time increased as the number of distractors increased in the feature-conjunction task for all groups, but more so for patients with AD or DLB than for any of the other groups. These results suggest that the single-feature search "pop-out" effect is preserved in DLB and AD patients, whereas ability to perform the feature-conjunction search is impaired. This pattern of preserved single-feature search with impaired feature-conjunction search is consistent with a deficit in feature binding that may be mediated by abnormalities in networks involving the dorsal occipito-parietal cortex.

ObjectiveVisual processing abilities of patients with dementia with Lewy bodies (DLB) or Alzheimer disease (AD) dementia were assessed psychophysically using a simple horizontal motion discrimination task that engages the dorsal visual processing stream.MethodsParticipants included patients with mild dementia with DLB, AD dementia or Parkinson disease (PD) with dementia (PDD), without dementia with PD, and normal controls. Participants indicated the left or right direction of coherently moving dots that were embedded within dynamic visual noise provided by randomly moving dots. The proportion of coherently moving dots was increased or decreased across trials to determine a threshold at which participants could correctly indicate their direction with greater than 80% accuracy.ResultsMotion discrimination thresholds of patients with DLB and PDD were comparable and significantly higher (i.e., worse) than those of patients with AD dementia. The thresholds of patients with AD dementia and patients with PD were normal. These results were confirmed in subgroups of patients with DLB/PDD and AD dementia with autopsy-confirmed disease. A motion discrimination threshold greater than 0.23 distinguished between DLB/PDD and AD dementia with 67% sensitivity and 85% specificity.ConclusionsDifferential deficits in detecting direction of simple horizontal motion suggest that dorsal processing stream dysfunction is greater in DLB and PDD than in AD dementia. Therefore, impaired performance on simple visual motion discrimination tasks that specifically engage occipitoparietal brain regions suggests the presence of Lewy body pathology.

Evidence from patients with amnesia suggests that recognition memory span tasks engage both long-term memory (i.e., secondary memory) processes mediated by the diencephalic-medial temporal lobe memory system and working memory processes mediated by fronto-striatal systems. Thus, the recognition memory span task may be particularly effective for detecting memory deficits in disorders that disrupt both memory systems. The presence of unique pathology in fronto-striatal circuits in Dementia with Lewy Bodies (DLB) compared to AD suggests that performance on the recognition memory span task might be differentially affected in the two disorders even though they have quantitatively similar deficits in secondary memory. In the present study, patients with autopsy-confirmed DLB or AD, and Normal Control (NC) participants, were tested on separate recognition memory span tasks that required them to retain increasing amounts of verbal, spatial, or visual object (i.e., faces) information across trials. Results showed that recognition memory spans for verbal and spatial stimuli, but not face stimuli, were lower in patients with DLB than in those with AD, and more impaired relative to NC performance. This was despite similar deficits in the two patient groups on independent measures of secondary memory such as the total number of words recalled from long-term storage on the Buschke Selective Reminding Test. The disproportionate vulnerability of recognition memory span task performance in DLB compared to AD may be due to greater fronto-striatal involvement in DLB and a corresponding decrement in cooperative interaction between working memory and secondary memory processes. Assessment of recognition memory span may contribute to the ability to distinguish between DLB and AD relatively early in the course of disease.

Our ability to remember past events requires not only storing enduring engrams or memory traces of these events, but also successfully reactivating these latent traces in response to appropriate cues at the time of retrieval—a process that has been termed ecphory. However, relatively little is known about the processes that facilitate the dynamic interactions between retrieval cues and stored memory traces that are critical for successful recognition and recollection. Recently, an intriguing link between pupil dilation and recognition memory has been identified, with studied items eliciting greater pupil dilation than unstudied items during retrieval. However, the processes contributing to this "pupillary old/new effect" remain unresolved, with current explanations suggesting that it reflects the strength of the underlying memory trace. Here, we explore the novel hypothesis that the pupillary old/new effect does not index memory strength alone, but rather reflects the facilitation of cue–trace interactions during episodic memory retrieval that may be supported by activity within the pupil‐linked locus coeruleus‐noradrenergic (LC‐NA) arousal system. First, we show that the magnitude of pupil dilation is influenced by the degree of overlap between cue and trace information. Second, we find that the magnitude of pupil dilation reflects the amount of study contextual information reinstated during retrieval. These findings provide a novel framework for understanding the pupillary old/new effect, and identify a potential role for the LC‐NA system in recognition memory retrieval. Our findings support the novel hypothesis that synergistic interactions between retrieval cues and memory trace information during episodic memory retrieval trigger activity within the pupil‐linked arousal system that in turn facilitates contextual retrieval. These findings serve to resolve conflicting theories of the pupillary old/new effect and provide a framework for understanding the role of the LC‐NA system in episodic memory. [ABSTRACT FROM AUTHOR]

Background: Pathological changes of Alzheimer's disease (AD) occur in the locus coeruleus (LC) years before clinical symptoms. This may affect LC activity that can be indexed by changes in pupil dilation. AD also disrupts connections between related but functionally distinct cortical areas leading to visual feature binding deficits. Thus, feature binding in individuals with preclinical AD may require additional cognitive effort that engages LC activity. Pupil dilation during conjunctive visual search may therefore be a particularly sensitive marker of preclinical AD. Method: Sixty‐three cognitively unimpaired older adults from the UCSD Alzheimer's Disease Research Center (51% men; overall mean age = 78.4 years, education = 17.5 years, and MoCA score = 25.9), performed a conjunctive visual search task while their pupil diameter was continuously recorded. There were 108 trials in which the participant searched for a target stimulus (a black dot moving up‐and‐down) among distractor stimuli that shared target features (white dots moving up‐and‐down and black dots moving left‐and‐right). Search displays contained 1, 3, or 5 stimuli with a target present on half of the trials. Reaction time and accuracy in detecting presence of a target were recorded. Plasma levels of the AD biomarker pTau181 were determined by the National Centralized Repository for Alzheimer's Disease using Quanterix (v2). Plasma pTau181>4.09 pg/mL was considered AD positive. Result: AD positive (n = 19) and AD negative (n = 44) groups did not differ on age, education, sex, or MoCA scores. Despite similar behavioral performance in visual search, the groups displayed striking differences in pupillary responses across conditions. Both groups showed more pupil dilation with increasing display size, consistent with the application of cognitive effort. However, only the AD‐positive group showed significantly greater pupil dilation in the target‐present than target‐absent condition. This selective pupil modulation in the AD‐positive group may reflect greater demands associated with maintaining the search template in working memory or with performing template‐matching processes to guide attention. Conclusion: Results suggest early functional changes in the LC noradrenergic system are detectable in biomarker‐positive cognitively healthy older adults. Pupillary responsivity under task‐induced conjunction search conditions may serve as a particularly sensitive marker of preclinical AD. [ABSTRACT FROM AUTHOR]

Objective. To investigate the behavioral and neural effects of rule-based knowledge on motor sequence learning. Methods. The authors developed a novel 2-dimensional variant of the serial reaction time (SRT) task [...]