Attentional dynamics and visual perception: mechanisms of spatial disorientation in Alzheimer's disease

Magnetoencephalographic brain activity evoked by the optic-flow task is correlated with β-amyloid burden and parahippocampal atrophy

Visuospatial perception is often impaired in people with Alzheimer's disease (AD). Because visuospatial information is thought to be processed in the visual dorsal stream, it is believed that brain activities in the dorsal stream will be altered in AD patients. In this study, we investigated whether regional brain activity related to visuospatial perception were associated with AD progression markers. An optic-flow task, which activates the dorsal stream associated with visuospatial perception, was performed, and the brain activities evoked by the task were evaluated using magnetoencephalography (MEG). First, we evaluated the responses to optic-flow stimuli in 21 cognitively unimpaired participants and determined the regions of interest (ROIs) where optic-flow activities were activated. Task-related activations were observed in 14 cortical regions including the dorsal stream: the right and left medial ventral occipital cortex (MVOcC), lateral occipital cortex (LOcC), precuneus (Pcun), inferior parietal lobule (IPL), superior parietal lobule (SPL), posterior superior temporal sulcus (pSTS), and fusiform gyri (FuG). Next, we performed correlation analyses between task-related activity in each ROI and two AD progression markers, global amyloid burden and parahippocampal gyrus (PHG) volume, for 25 participants who underwent amyloid positron emission tomography (PET) scans. We found that the global amyloid burden was negatively correlated with task-related activity in the left MVOcC and right SPL [r = -0.488 (p = 0.013) and r = -0.421 (p = 0.038), respectively]. Furthermore, significant positive correlations were observed between PHG volume and task-related activity in both the left and right SPL [r = 0.500 (p = 0.011) and r = 0.549 (p = 0.005), respectively]. Since the SPL is known to be responsible for visuospatial perception, these results suggest that MEG neuronal activity of patients performing the optic-flow activity can detect changes in brain activity associated with visuospatial impairment related to AD.

Auxiliary diagnostic method of Parkinson's disease based on eye movement analysis in a virtual reality environment

Eye movement dysfunction is one of the non-motor symptoms of Parkinson's disease (PD). An accurate analysis method for eye movement is an effective way to gain a deeper understanding of the nervous system function of PD patients. However, currently, there are only a few assistive methods available to help physicians conveniently and consistently assess patients suspected of having PD. To solve this problem, we proposed a novel visual behavioral analysis method using eye tracking to evaluate eye movement dysfunction in PD patients automatically. This method first provided a physician task simulation to induce PD-related eye movements in Virtual Reality (VR). Subsequently, we extracted eye movement features from recorded eye videos and applied a machine learning algorithm to establish a PD diagnostic model. Then, we collected eye movement data from 66 participants (including 22 healthy controls and 44 PD patients) in a VR environment for training and testing during visual tasks. Finally, on this relatively small dataset, the results reveal that the Support Vector Machine (SVM) algorithm has better classification potential.

Use of Virtual Reality to Improve Spatial Orientation in Alzheimer's Disease and Mild Cognitive Impairment: A Systematic Review

BACKGROUND

Alzheimer's disease is a chronic, neurodegenerative condition that leads to a significant cognitive decline. One of the symptoms that greatly reduces the quality of daily functioning is the deterioration of spatial orientation abilities. A non-pharmacological treatment option for Alzheimer's disease, which is also employed to improve the cognitive functioning of individuals with mild cognitive impairment, is virtual reality training.

OBJECTIVE

To the best of the authors' knowledge, there is no existing systematic review on the use of virtual reality training to enhance spatial orientation in individuals with Alzheimer's disease or mild cognitive impairment. The review was therefore conducted to fill this gap. The findings of this review may support the efficacy of virtual reality in enhancing spatial orientation.

METHODS

Five databases were searched. The primary inclusion criteria were study participants aged over 60 years with a diagnosis of Alzheimer's disease or mild cognitive impairment and the use of virtual reality for improving spatial orientation. Six studies meeting these criteria were ultimately included in the review.

RESULTS

All included studies demonstrated an improvement in the spatial orientation of individuals with Alzheimer's disease or mild cognitive impairment following virtual reality training. This indicates the effectiveness of virtual reality technology in cognitive rehabilitation.

CONCLUSION

As virtual reality cognitive training has proven effective, its use should be more widely adopted. Further research on the application of virtual reality for enhancing spatial orientation in individuals with dementia is recommended.

Evaluating the feasibility of cognitive impairment detection in Alzheimer's disease screening using a computerized visual dynamic test

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease without known cure. However, early medical treatment can help control its progression and postpone intellectual decay. Since AD is preceded by a period of cognitive deterioration, the effective assessment of cognitive capabilities is crucial to develop reliable screening procedures. For this purpose, cognitive tests are extensively used to evaluate cognitive areas such as language, attention, or memory.

METHODS

In this work, we analyzed the potential of a visual dynamics evaluation, the rapid serial visual presentation task (RSVP), for the detection of cognitive impairment in AD. We compared this evaluation with two of the most extended brief cognitive tests applied in Spain: the Clock-drawing test (CDT) and the Phototest. For this purpose, we assessed a group of patients (mild AD and mild cognitive impairment) and controls, and we evaluated the ability of the three tests for the discrimination of the two groups.

RESULTS

The preliminary results obtained suggest the RSVP performance is statistically higher for the controls than for the patients (p-value = 0.013). Furthermore, we obtained promising classification results for this test (mean accuracy of 0.91 with 95% confidence interval 0.72, 0.97).

CONCLUSIONS

Since the RSVP is a computerized, auto-scored, and potentially self-administered brief test, it could contribute to speeding-up cognitive impairment screening and to reducing the associated costs. Furthermore, this evaluation could be combined with other tests to augment the efficiency of cognitive impairment screening protocols and to potentially monitor patients under medical treatment.

Immunotherapy with Cleavage-Specific 12A12mAb Reduces the Tau Cleavage in Visual Cortex and Improves Visuo-Spatial Recognition Memory in Tg2576 AD Mouse Model

Tau-targeted immunotherapy is a promising approach for treatment of Alzheimer's disease (AD). Beyond cognitive decline, AD features visual deficits consistent with the manifestation of Amyloid β-protein (Aβ) plaques and neurofibrillary tangles (NFT) in the eyes and higher visual centers, both in animal models and affected subjects. We reported that 12A12-a monoclonal cleavage-specific antibody (mAb) which in vivo neutralizes the neurotoxic, N-terminal 20-22 kDa tau fragment(s)-significantly reduces the retinal accumulation in Tg(HuAPP695Swe)2576 mice of both tau and APP/Aβ pathologies correlated with local inflammation and synaptic deterioration. Here, we report the occurrence of N-terminal tau cleavage in the primary visual cortex (V1 area) and the beneficial effect of 12A12mAb treatment on phenotype-associated visuo-spatial deficits in this AD animal model. We found out that non-invasive administration of 12 A12mAb markedly reduced the pathological accumulation of both truncated tau and Aβ in the V1 area, correlated to significant improvement in visual recognition memory performance along with local increase in two direct readouts of cortical synaptic plasticity, including the dendritic spine density and the expression level of activity-regulated cytoskeleton protein Arc/Arg3.1. Translation of these findings to clinical therapeutic interventions could offer an innovative tau-directed opportunity to delay or halt the visual impairments occurring during AD progression.

Non-Pharmacological Interventions for Wandering/Aberrant Motor Behaviour in Patients with Dementia

Background: Aberrant motor behaviour or wandering refers to aimless movement without a specific purpose. Wandering is common in patients with dementia and leads to early institutionalization and caregivers’ burden. Non-pharmacological interventions should be also considered as a first-line solution for the wandering because current pharmacological treatment has serious side-effects. Methods: A cross-over randomised controlled trial (RCT) with 60 participants of all stages and different types of dementia was conducted in Greece. The sample was randomly assigned in 6 different groups of 10 participants each. Every intervention lasted for 5 days, and there were 2 days as a wash-out period. There was no drop-out rate. The measurements used were the Mini Mental State Examination (MMSE), Addenbrooke’s Cognitive Examination Revised (ACE-R), Geriatric Depression Scale (GDS), Functional Rating Scale for Symptoms in Dementia (FRSSD), and Neuropsychiatric Inventory (NPI). The interventions that were evaluated were reminiscence therapy (RT), music therapy (MT), and physical exercise (PE). Results: NPI scores were reduced in the group receiving PE (p = 0.006). When MT (p = 0.018) follows PE, wandering symptoms are reduced further. RT should follow MT in order to reduce wandering more (p = 0.034). The same combination was effective for the caregivers’ burden as well; PE (p = 0.004), MT (p = 0.036), RT (p = 0.039). Conclusions: An effective combination that can reduce wandering symptoms in all stages and types of dementia was found: The best order was PH-MT-RT. The same combination in the same order reduced caregivers’ burden.

Stereoscopic Depth Perception and Visuospatial Dysfunction in Alzheimer's Disease

With visuospatial dysfunction emerging as a potential marker that can detect Alzheimer's disease (AD) even in its earliest stages and with disturbance in stereopsis suspected to be the prime contributor to visuospatial deficits in AD, we assessed stereoscopic abilities of patients with AD and mild cognitive impairment (MCI). Whereas previous research assessing patients' stereoacuity has yielded mixed results, we assessed patients' capacity to process coarse disparities that can convey adequate depth information about objects in the environment. We produced two virtual cubes at two different distances from the observer by manipulating disparity type (absolute vs. relative), disparity direction (crossed vs. uncrossed) and disparity magnitude, then had participants judge the object that appeared closer to them. Two patient groups performed as well as, or even better than elderly controls, suggesting that AD patients' coarse disparity processing capacity is capable of supporting common tasks involving reaching, grasping, driving, and navigation. Results may help researchers narrow down the exact cause(s) of visuospatial deficits in AD and develop and validate measures to assess visuospatial dysfunction in clinical trials and disease diagnosis.

Hyperexcitability in Aging Is Lost in Alzheimer's: What Is All the Excitement About?

Neuronal hyperexcitability has emerged as a potential biomarker of late-onset early-stage Alzheimer's disease (LEAD). We hypothesize that the aging-related posterior cortical hyperexcitability anticipates the loss of excitability with the emergence of impairment in LEAD. To test this hypothesis, we compared the behavioral and neurophysiological responses of young and older (ON) normal adults, and LEAD patients during a visuospatial attentional control task. ONs show frontal cortical signal incoherence and posterior cortical hyper-responsiveness with preserved attentional control. LEADs lose the posterior hyper-responsiveness and fail in the attentional task. Our findings suggest that signal incoherence and cortical hyper-responsiveness in aging may contribute to the development of functional impairment in LEAD.

Eye Tracking Analysis of Visual Cues during Wayfinding in Early Stage Alzheimer's Disease

INTRODUCTION

Persons with Alzheimer's disease (AD) have profound impairment in wayfinding, potentially related to a deficit in visual attention and selection of relevant environmental information. This study sought to determine differences in visual attention to salient visual cues and nonsalient cues (building features) in older adults with and without AD during active wayfinding in a large-scale, virtual reality spatial task.

METHODS

Fifteen subjects (7 with AD and 8 controls without AD) were asked to find their way repeatedly during 10 trials in a virtual simulation of a senior retirement community. Subjects wore eye tracking glasses to capture visual fixations while wayfinding. The least square means (LSMs) and their standard errors (SEs) for percentage of fixations and duration of fixations on salient and nonsalient cues were estimated from the linear mixed effects models and compared by group (AD or control) and cue type.

RESULTS

The group by cue type interaction was significant for both percentage of fixations (F(1, 13) = 6.79, p = 0.02) and duration of fixations (F(1, 13) = 4.87, p = 0.04). The AD group had significantly lower percentages of fixations on salient cues, LSM = 57.91 (SE = 2.44), compared to controls, LSM = 66.40 (SE = 2.19); p = 0.03. Persons with AD had a higher percentage of fixations on building features, LSM = 31.65 (SE = 2.18), than controls, LSM = 24.54 (SE = 1.95); p = 0.02. Shorter durations of fixations on salient cues were experienced by the AD group, LSM = 38.89 (SE = 1.69), than the control group, LSM = 44.69 (SE = 1.55); p = 0.02.

DISCUSSION/CONCLUSION

Individuals with AD may have difficulty selecting relevant information for wayfinding as compared to normally aging individuals and attend more frequently than controls to irrelevant information. This may help explain the wayfinding difficulties seen in AD.

Distinct forms of motion sensitivity impairments in Alzheimer's disease

Motion sensitivity impairment in Alzheimer’s disease (AD) is often characterized as elevated coherence threshold. An alternative way to measure motion sensitivity is the direction threshold, i.e., the minimal angle of motion direction that can be discriminated. So far, it is less clear whether and how the direction threshold is altered in AD. Here we asked a group of AD patients and two control groups of healthy participants (young and elderly adults) to judge their perceived heading direction based on a field of optic flow stimuli simulating a forward translation in the environment. We manipulated the heading direction and the coherence of the optic flow independently and measured the direction and coherence thresholds from each participant. We found that the direction threshold increased significantly in AD patients as compared to healthy controls, like the coherence threshold. Yet, the elevation in the direction threshold was less pronounced than the coherence threshold. Moreover, the magnitudes of the direction and coherence thresholds in AD patients were not correlated. Our results suggest that coherence and direction impairments are two distinct forms of motion deficits in AD patients which might be associated with independent neural mechanisms.

FDG PET Findings according to Wandering Patterns of Patients with Drug-naïve Alzheimer's Disease

Background and Purpose

To explore anatomic substrate of specific wandering patterns in patients with Alzheimer's disease (AD) by performing positron emission tomography with ¹⁸F fluorodeoxyglucose positron emission tomography (FDG PET).

Methods

Drug-naïve AD patients with wandering (n=80) and without wandering (n=262) were recruited. First, the specific pattern of wandering type was operationally classified according to specific wandering score and clinical assessment. Second, brain FDG PET was performed and fluorodeoxyglucose (FDG) uptake differences of specific brain regions according to wandering patterns were compared to those of non-wanderers.

Results

In patients with pacing pattern, FDG PET showed significant lower FDG uptake in both middle cingulum and left putamen cluster compared to non-wanderers. The right precuneus and supplementary motor area in patients with random pattern and left calcarine sulcus, right calcarine sulcus, right middle cingulum, and right post central gyrus in patients with lapping pattern had significantly lower FDG uptake compared to non-wanderers.

Conclusions

This study showed that wandering in patients with AD had three distinct patterns. These specific patterns showed significant lower FDG uptake in specific brain areas compared to non-wanderers.

Active Navigation in Virtual Environments Benefits Spatial Memory in Older Adults

We investigated age differences in memory for spatial routes that were either actively or passively encoded. A series of virtual environments were created and presented to 20 younger (Mean age = 19.71) and 20 older (Mean age = 74.55) adults, through a cardboard viewer. During encoding, participants explored routes presented within city, park, and mall virtual environments, and were later asked to re-trace their travelled routes. Critically, participants encoded half the virtual environments by passively viewing a guided tour along a pre-selected route, and half through active exploration with volitional control of their movements by using a button press on the viewer. During retrieval, participants were placed in the same starting location and asked to retrace the previously traveled route. We calculated the percentage overlap in the paths travelled at encoding and retrieval, as an indicator of spatial memory accuracy, and examined various measures indexing individual differences in their cognitive approach and visuo-spatial processing abilities. Results showed that active navigation, compared to passive viewing during encoding, resulted in a higher accuracy in spatial memory, with the magnitude of this memory enhancement being significantly larger in older than in younger adults. Regression analyses showed that age and score on the Hooper Visual Organizational test predicted spatial memory accuracy, following the passive and active encoding of routes. The model predicting accuracy following active encoding additionally included the distance of stops from an intersection as a significant predictor, illuminating a cognitive approach that specifically contributes to memory benefits in following active navigation. Results suggest that age-related deficits in spatial memory can be reduced by active encoding.

Neurocognitive Assessment in Virtual Reality Through Behavioral Response Analysis

The ability to detect and diagnose neurocognitive disorders at the earliest possible moment is key to a better prognosis for the patient. Two of the earliest indicators of potential neurocognitive problems are motor and visual dysfunction. Motor disorders and problems in visual cognition can be seen in many neurocognitive disorders, resulting in abnormal physical reactions to visual stimuli. Analyzing physical behaviors when presented with such stimuli can provide insights into the visual perception and motor abilities of an individual, yet there is currently no unbiased, objective, general-purpose tool that analyzes attention and motor behavior to assess neurocognitive function. We propose a novel method of neurocognitive function assessment that tests the patient's cognition using virtual reality with eye tracking and motion analysis. By placing the patient in a controlled virtual environment and analyzing their movements, we can evoke certain physical responses from subjects for neurocognitive assessment. We have developed a prototype system that places the subject in a virtual baseball field and captures their full body motion as they try to catch baseballs. This scenario tests the subject's ability to determine the landing time and position of the ball, as well as the test subject's balance, motor skills, attention, and memory. Preliminary tests with 20 healthy normal individuals demonstrate the ability of this tool to assess the test subject's balance, memory, attention, and reaction to visual stimuli. This platform has a twofold contribution: it is used to assess several neurocognitive constructs that affect visual and motor capability neutrally and objectively based on controlled stimuli, and it enables objective comparison between different neurocognitive disorders research in this field.

Attentional ERPs distinguish aging and early Alzheimer's dementia

The early detection of Alzheimer's disease requires our distinguishing it from cognitive aging. Here, we test whether spatial attentional changes might support that distinction. We engaged young normal (YN), older normal (ON), and patients with early Alzheimer's dementia (EAD) in an attentionally cued, self-movement heading discrimination task while we recorded push-button response times and event related potentials. YNs and ONs show the behavioral effects of attentional shifts from the cue to the target, whereas EAD patients did not (p < 0.001). YNs and ONs also show the shifting lateralization of a newly described attentional event related potentials component, whereas EAD patients did not (p < 0.001). Our findings suggest that spatial inattention in EAD patients may contribute to heading direction processing impairments that distinguish them from ONs and undermine their navigational capacity and driving safety.

Impaired Center-Surround Suppression in Patients with Alzheimer's Disease

Alzheimer's disease (AD) is often associated with declined visual processing abilities. Here we tested whether the functions of center-surround suppression- a hallmark property in the visual system- are altered by AD. To this end, we recruited three groups of participants (AD, elderly, and young) in a motion direction discrimination task, in which we measured the temporal duration threshold of a  drifting Gabor with varying stimulus sizes. We first replicated the phenomena of center-surround suppression that the required duration for discriminating a high contrast grating decreases with increasing stimulus size. We then showed that the magnitudes of suppression varied among the three groups. There was progressive reduction of suppression in the elderly and AD groups compared with the young group. Interestingly, we found that the levels of suppression can predict the severity of dementia in the AD group. Our results suggest that AD is associated with impaired center-surround functions in the visual motion processing pathway.

The influence of visual flow and perceptual load on locomotion speed

Visual flow is used to perceive and regulate movement speed during locomotion. We assessed the extent to which variation in flow from the ground plane, arising from static visual textures, influences locomotion speed under conditions of concurrent perceptual load. In two experiments, participants walked over a 12-m projected walkway that consisted of stripes that were oriented orthogonal to the walking direction. In the critical conditions, the frequency of the stripes increased or decreased. We observed small, but consistent effects on walking speed, so that participants were walking slower when the frequency increased compared to when the frequency decreased. This basic effect suggests that participants interpreted the change in visual flow in these conditions as at least partly due to a change in their own movement speed, and counteracted such a change by speeding up or slowing down. Critically, these effects were magnified under conditions of low perceptual load and a locus of attention near the ground plane. Our findings suggest that the contribution of vision in the control of ongoing locomotion is relatively fluid and dependent on ongoing perceptual (and perhaps more generally cognitive) task demands.

Disrupted pursuit compensation during self-motion perception in early Alzheimer's disease

Our perception of the world is remarkably stable despite of distorted retinal input due to frequent eye movements. It is considered that the brain uses corollary discharge, efference copies of signals sent from motor to visual regions, to compensate for distortions and stabilize visual perception. In this study, we tested whether patients with Alzheimer’s disease (AD) have impaired corollary discharge functions as evidenced by reduced compensation during the perception of optic flow that mimics self-motion in the environment. We asked a group of early-stage AD patients and age-matched healthy controls to indicate the perceived direction of self-motion based on optic flow while tracking a moving target with smooth pursuit eye movement, or keeping eye fixation at a stationary target. We first replicated the previous findings that healthy participants were able to compensate for distorted optic flow in the presence of eye movements, as indicated by similar performance of self-motion perception between pursuit and fixation conditions. In stark contrast, AD patients showed impaired self-motion perception when the optic flow was distorted by eye movements. Our results suggest that early-stage AD pathology is associated with disrupted eye movement compensation during self-motion perception.

Altered motion repulsion in Alzheimer's disease

Recent research in Alzheimer’s disease (AD) indicates that perceptual impairments may occur before the onset of cognitive declines, and can thus serve as an early noninvasive indicator for AD. In this study, we focused on visual motion processing and explored whether AD induces changes in the properties of direction repulsion between two competing motions. We used random dot kinematograms (RDKs) and measured the magnitudes of direction repulsion between two overlapping RDKs moving different directions in three groups of participants: an AD group, an age-matched old control group, and a young control group. We showed that motion direction repulsion was significantly weaker in AD patients as comparing to both healthy controls. More importantly, we found that the magnitude of motion repulsion was predictive of the assessment of clinical severity in the AD group. Our results implicate that AD pathology is associated with altered neural functions in visual cortical areas and that motion repulsion deficit is a behavioral biomarker for the tracking of AD development.

Comparing the Sensitivity, Specificity, and Predictive Values of the Montreal Cognitive Assessment and Mini-Mental State Examination When Screening People for Mild Cognitive Impairment and Dementia in Chinese Population

BACKGROUND

The study compared the sensitivity, specificity, and diagnostic value of the Montreal Cognitive Assessment (MoCA) and Mini-Mental State Examination (MMSE) in screening for mild cognitive impairment (MCI) and dementia.

METHODS

A cross-sectional descriptive design was used, and 142 participants were screened for MCI and mild dementia by using the MoCA and MMSE. The receiver operating characteristic curves and the cutoff scores with the largest area under the curve (AUC) were determined and compared to calculate the sensitivity, specificity, and diagnostic value (positive predictive value [PPV] and negative predictive value [NPV]).

RESULTS

The optimal MoCA cutoff scores for MCI and dementia were 24 and 20, respectively. According to these scores, the sensitivities were 0.88 and 0.79, the specificities were 0.74 and 0.80, the AUCs were 0.91 and 0.87, the PPVs were 0.93 and 0.74, and the NPVs were 0.74 and 0.87, respectively. The optimal cutoff MMSE scores for MCI and dementia were 27 and 24, respectively. Hence, the sensitivities were 0.88 and 0.84, the specificities were 0.70 and 0.86, the AUCs were 0.88 and 0.89, the PPVs were 0.94 and 0.80, and the NPVs were 0.81 and 0.88, respectively.

CONCLUSION

In the Chinese population, the MoCA is more efficient in screening for MCI than for dementia, whereas the MMSE is more efficient in screening for dementia than for MCI. The MoCA and MMSE can be used by clinical staffs for quick and accurate cognitive impairment screening, thus facilitating early and appropriate clinical intervention and treatment.

A Relationship between Depression and Wandering in Community-Dwelling Elders with Dementia

Background and Purpose

Wandering is one of the most common behavioral and psychological symptoms of dementia, and associated with some of the adverse outcomes in dementia, such as getting lost or even death. The etiology of wandering is not yet clearly known. As depression and wandering are both very common among the patients with dementia, this study examined the relationship between the depression and wandering among the community dwelling patients with dementia.

Methods

Fifty community dwelling patients diagnosed with dementia were included in this study if they had primary family caregiver, older than age 18 in Seoul, South Korea. The Geriatric Depression Scale, Korean Version (GDS-K), Korean Version of the Mini-Mental State Examination (K-MMSE) and Korean Version of Revised Algase Wandering Scale-Community Version (K-RAWS-CV) were used to measure the severity of depression, cognitive function and wandering.

Results

Thirty percents of the patients showed wandering. Mean score of GDS-K was significantly higher in wanderers than non-wanderers. Severity of depression was significantly correlated with the total score of K-RAWS-CV and subscales of persistent walking, repetitive walking, eloping behavior, and mealtime impulsivity in whole sample. K-MMSE score also was related to wandering behavior. The prevalence odds ratio for wandering in depressed patients compared with undepressed group was 8.386 (95% confidence interval: 1.978–35.561).

Conclusions

This study implicates that not only cognitive impairment but also psychosocial aspects should be considered in wandering patients with dementia and suggests assessing the depression in patients would be helpful in identifying the causes of wandering.

Wayfinding in ageing and Alzheimer's disease within a virtual senior residence: study protocol

AIM

To report a study protocol that examines the impact of adding salient cues in a virtual reality simulation of a senior residential building on wayfinding for older adults with and without Alzheimer's disease.

BACKGROUND

An early symptom of Alzheimer's disease is the inability to find one's way (wayfinding). Senior residential environments are especially difficult for wayfinding. Salient cues may be able to help persons with Alzheimer's disease find their way more effectively so they can maintain independence.

DESIGN

A repeated measures, within and between subjects design.

METHODS

This study was funded by the National Institutes of Health (August 2012). Older adults (N = 40) with normal cognition and older adults with early stage Alzheimer's disease/mild cognitive impairment (N = 40) will try to find their way to a location repeatedly in a virtual reality simulation of senior residence. There are two environments: standard (no cues) and salient (multiple cues). Outcome measures include how often and how quickly participants find the target location in each cue condition.

CONCLUSION

The results of this study have the potential to provide evidence for ways to make the environment more supportive for wayfinding for older adults with Alzheimer's disease. This study is registered at Trialmatch.alz.org (Identifier 260425-5).

Better Utilization of Mouse Models of Neurodegenerative Diseases in Preclinical Studies: From the Bench to the Clinic

The major symptom of Alzheimer's disease is dementia progressing with age. Its clinical diagnosis is preceded by a long prodromal period of brain pathology that encompasses both formation of extracellular amyloid and intraneuronal tau deposits in the brain and widespread neuronal death. At present, familial cases of dementia provide the most promising foundation for modeling neurodegenerative tauopathies, a group of heterogeneous disorders characterized by prominent intracellular accumulation of hyperphosphorylated tau protein. In this chapter, we describe major behavioral hallmarks of tauopathies, briefly outline the genetics underlying familial cases, and discuss the arising implications for modeling the disease in transgenic mouse systems. The selection of tests performed to evaluate the phenotype of a model should be guided by the key behavioral hallmarks that characterize human disorder and their homology to mouse cognitive systems. We attempt to provide general guidelines and establish criteria for modeling dementia in a mouse; however, interpretations of obtained results should avoid a reductionist "one gene, one disease" explanation of model characteristics. Rather, the focus should be directed to the question of how the mouse genome can cope with the over-expression of the protein coded by transgene(s). While each model is valuable within its own constraints and the experiments performed are guided by specific hypotheses, we seek to expand upon their methodology by offering guidance spanning from issues of mouse husbandry to choices of behavioral tests and routes of drug administration that might increase the external validity of studies and consequently optimize the translational aspect of preclinical research.

Perceiving Collision Impacts in Alzheimer's Disease: The Effect of Retinal Eccentricity on Optic Flow Deficits

The present study explored whether the optic flow deficit in Alzheimer's disease (AD) reported in the literature transfers to different types of optic flow, in particular, one that specifies collision impacts with upcoming surfaces, with a special focus on the effect of retinal eccentricity. Displays simulated observer movement over a ground plane toward obstacles lying in the observer's path. Optical expansion was modulated by varying [Formula: see text]. The visual field was masked either centrally (peripheral vision) or peripherally (central vision) using masks ranging from 10° to 30° in diameter in steps of 10°. Participants were asked to indicate whether their approach would result in "collision" or "no collision" with the obstacles. Results showed that AD patients' sensitivity to [Formula: see text] was severely compromised, not only for central vision but also for peripheral vision, compared to age- and education-matched elderly controls. The results demonstrated that AD patients' optic flow deficit is not limited to radial optic flow but includes also the optical pattern engendered by [Formula: see text]. Further deterioration in the capacity to extract [Formula: see text] to determine potential collisions in conjunction with the inability to extract heading information from radial optic flow would exacerbate AD patients' difficulties in navigation and visuospatial orientation.

The effect of spatio-temporal distance between visual stimuli on information processing in children with Specific Language Impairment

The purpose of this study is to evaluate whether children with Specific Language Impairment (SLI) have a deficit in processing a sequence of two visual stimuli (S1 and S2) presented at different inter-stimulus intervals and in different spatial locations. In particular, the core of this study is to investigate whether S1 identification is disrupted due to a retroactive interference of S2. To this aim, two experiments were planned in which children with SLI and children with typical development (TD), matched by age and non-verbal IQ, were compared (Experiment 1: SLI n=19; TD n=19; Experiment 2: SLI n=16; TD n=16). Results show group differences in the ability to identify a single stimulus surrounded by flankers (Baseline level). Moreover, children with SLI show a stronger negative interference of S2, both for temporal and spatial modulation. These results are discussed in the light of an attentional processing limitation in children with SLI.

Attentional blink in children with attention deficit hyperactivity disorder

OBJECTIVE

To explore the temporal mechanism of attention in children with attention deficit hyperactivity disorder (ADHD) and controls using a rapid serial visual presentation (RSVP) task in which two letters (T1 and T2) were presented in close temporal proximity among distractors (attentional blink [AB]).

METHOD

Thirty children aged between 9 and 13 years (12 with ADHD combined type and 18 controls) took part in the study. Both groups performed two kinds of RSVP task. In the single task, participants simply had to identify a target letter (T1), whereas in the dual task, they had to identify a target letter (T1) and a probe letter (T2).

RESULTS

The ADHD and control groups were equivalent in their single-task performance. However, in the dual-task condition, there were significant between-group differences in the rate of detection of the probe letter (T2) at lag + 1 and lag + 4. The ADHD group exhibited a larger overall AB compared with controls.

CONCLUSION

Our findings provide support for a link between ADHD and attentional blink.

Might cortical hyper-responsiveness in aging contribute to Alzheimer's disease?

Our goal is to understand the neural basis of functional impairment in aging and Alzheimer's disease (AD) to be able to characterize clinically significant decline and assess therapeutic efficacy. We used frequency-tagged ERPs to word and motion stimuli to study the effects of stimulus conditions and selective attention. ERPs to word or motion increase when a task-irrelevant 2nd stimulus is added, but decrease when the task is moved to that 2nd stimulus. Spectral analyses show task effects on response power without 2nd stimulus effects. However, phase coherence shows both 2nd stimulus and task effects. Thus, power and coherence are dissociably modulated by stimulus and task effects. Task-dependent phase coherence successively declines in aging and AD. In contrast, task-dependent spectral power increases in aging, only to decrease in AD. We hypothesize that age-related declines in signal coherence, associated with increased power generation, stresses neurons and contributes to the loss of response power and the development of functional impairment in AD.

Wandering and dementia

Wandering represents one of many behavioural problems occurring in people with dementia. To consider the phenomenon of wandering behaviour in demented patients, we conducted searches using Medline and Google Scholar to find relevant articles, chapters, and books published since 1975. Search terms used included 'wandering', 'behavioural and psychological symptoms', 'dementia', 'nursing', and 'elopements'. Publications found through this indexed search were reviewed for further relevant references. The term 'wandering' covers different types of behaviour, including aimless movement without a discernible purpose. It is associated with a variety of negatives outcomes. The aetiology of wandering is poorly understood and it remains an unsolved riddle. Wandering is an acutely distressing problem worldwide, both for the patients and caregivers, and it is a major reason for nursing home admission. Evidence on the effectiveness of pharmacological and non-pharmacological interventions is limited. It is possible that management of coexistent psychopathology would help to ameliorate this problematic behavioural disorder.

Visual attentional engagement deficits in children with specific language impairment and their role in real-time language processing

In order to become a proficient user of language, infants must detect temporal cues embedded within the noisy acoustic spectra of ongoing speech by efficient attentional engagement. According to the neuro-constructivist approach, a multi-sensory dysfunction of attentional engagement - hampering the temporal sampling of stimuli - might be responsible for language deficits typically shown in children with Specific Language Impairment (SLI). In the present study, the efficiency of visual attentional engagement was investigated in 22 children with SLI and 22 typically developing (TD) children by measuring attentional masking (AM). AM refers to impaired identification of the first of two sequentially presented masked objects (O1 and O2) in which the O1-O2 interval was manipulated. Lexical and grammatical comprehension abilities were also tested in both groups. Children with SLI showed a sluggish engagement of temporal attention, and individual differences in AM accounted for a significant percentage of unique variance in grammatical performance. Our results suggest that an attentional engagement deficit - probably linked to a dysfunction of the right fronto-parietal attentional network - might be a contributing factor in these children's language impairments.

Deeper attentional masking by lateral objects in children with autism

Autism spectrum disorder (ASD) is often associated with a detail-oriented perception and overselective attention in visual tasks, such as visual search and crowding. These results were obtained manipulating exclusively the spatial properties of the stimuli: few is known about the spatio-temporal dynamics of visual processing in ASD. In this study we employed an attentional masking (AM) paradigm comparing children with ASD and IQ-matched typically developing (TD) controls. The AM effect refers to an impaired identification of a target followed by a competitive masking object at different proximities in space and time. We found that ASD and TD groups did not differ in the AM effect provoked by the competitive object displayed in the same position of the target. In contrast, children with ASD showed a deeper and prolonged interference than the TD group when the masking object was displayed in the lateral position. These psychophysical results suggest that the inefficient attentional selection in ASD depends on the spatio-temporal interaction between competitive visual objects. These evidence are discussed in the light of the ASD altered neural connectivity hypothesis and the reentrant theory of perception.

Abnormal temporal dynamics of visual attention in Alzheimer's disease and in dementia with Lewy bodies

Although attentional control processes are disproportionately impaired in dementia with Lewy bodies (DLB) compared with dementia of the Alzheimer type (DAT), previous studies have not compared directly the temporal dynamics of visual attention in DLB and DAT. We examined the magnitude of the attentional blink (AB) effect in these patients, to determine the degree to which each patient group exhibited a deficit in selecting and processing visual stimuli presented in rapid succession. Eighteen DAT, 15 DLB patients, and 33 elderly controls were tested in a rapid serial visual presentation task. Participants were asked to report 1 (single-target condition) or 2 target letters (dual-target condition) embedded in a sequence of digit distracters. The temporal dynamics of visual attention was examined by varying the number of intervening distracters between the 2 targets in the dual-target condition and by estimating the attentional blink effect as the decline in the ability to report the second target correctly after successfully identifying the first. Patients with DLB performed significantly worse than patients with DAT and controls in both the single and dual-targets conditions. In contrast, DAT patients showed a selective impairment in the dual-target condition as compared with controls. As predicted, we found that both patients with DAT and DLB showed a more pronounced and protracted attentional blink than controls, indicating a reduced ability to re-engage attention on the second target. Furthermore, when DAT and DLB patients were able to report the second target, they frequently failed to identify the first, an effect that was absent in elderly controls and particularly large and long-lasting in DLB patients. This study suggests that both DLB and DAT patients show abnormal temporal dynamics of visual selective attention, presumably due to a greater intertarget competition for limited processing capacity. More generally, these findings reinforce the notion that deficits of attentional control processes are more severe in DLB patients as compared with DAT patients.

Acute effects of donepezil in healthy young adults underline the fractionation of executive functioning

The cholinergic system is involved in the modulation of both bottom-up and top-down attentional control. Top-down attention engages multiple executive control processes, but few studies have investigated whether all or selective elements of executive functions are modulated by the cholinergic system. To investigate the acute effects of the pro-cholinergic donepezil in young, healthy volunteers on distinct components of executive functions we conducted a double-blind, placebo-controlled, independent-groups design study including 42 young healthy male participants who were randomly assigned to one of three oral treatments: glucose (placebo), donepezil 5 mg or donepezil 7.5 mg. The test battery included measures of different executive components (shifting, updating, inhibition, dual-task performance, planning, access to long-term memory), tasks that evaluated arousal/vigilance/visuomotor performance, as well as functioning of working memory subsidiary systems. Donepezil improved sustained attention, reaction times, dual-task performance and the executive component of digit span. The positive effects in these executive tasks did not correlate with arousal/visuomotor/vigilance measures. Among the various executive domains investigated donepezil selectively increased dual-task performance in a manner that could not be ascribed to improvement in arousal/vigilance/visuomotor performance nor working memory slave systems. Other executive tasks that rely heavily on visuospatial processing may also be modulated by the cholinergic system.

Landmark recognition in Alzheimer's dementia: spared implicit memory for objects relevant for navigation

Background

In spatial navigation, landmark recognition is crucial. Specifically, memory for objects placed at decision points on a route is relevant. Previous fMRI research in healthy adults showed higher medial-temporal lobe (MTL) activation for objects placed at decision points compared to non-decision points, even at an implicit level. Since there is evidence that implicit learning is intact in amnesic patients, the current study examined memory for objects relevant for navigation in patients with Alzheimer’s dementia (AD).

Methodology/Principal Findings

21 AD patients participated with MTL atrophy assessed on MRI (mean MMSE = 21.2, SD = 4.0), as well as 20 age- and education-matched non-demented controls. All participants watched a 5-min video showing a route through a virtual museum with 20 objects placed at intersections (decision points) and 20 at simple turns (non-decision points). The instruction was to pay attention to the toys (half of the objects) for which they were supposedly tested later. Subsequently, a recognition test followed with the 40 previously presented objects among 40 distracter items (both toys and non-toys). Results showed a better performance for the non-toy objects placed at decision points than non-decision points, both for AD patients and controls.

Conclusion/Significance

Our findings indicate that AD patients with MTL damage have implicit memory for object information relevant for navigation. No decision point effect was found for the attended items. Possibly, focusing attention on the items occurred at the cost of the context information in AD, whereas the controls performed at an optimal level due to intact memory function.

Distinct visual motion processing impairments in aging and Alzheimer's disease

Aging and Alzheimer's disease (AD) are associated with declines in the visual perception of self-movement that undermine navigation and independent living. We studied 214 subjects' heading direction and speed discrimination using the radial patterns of visual motion in optic flow. Young (YA), middle-aged (MA), and older normal (ON) subjects, and AD patients viewed optic flow in which we manipulated the motion coherence, spatial texture, and temporal periodicity composition of the visual display. Aging and AD were associated with poorer heading and speed perception at lower temporal periodicity, with smaller effects of spatial texture. AD patients were particularly impaired by motion incoherence created by adding randomly moving dots to the optic flow. We conclude that visual motion processing is impaired by distinct mechanisms in aging and the transition to AD, implying distinct neural mechanisms of impairment.

Attentional blink and repetition blindness

When two masked, to-be-attended targets are presented within half a second of each other, report accuracy for the second target (T2) is impaired relative to when the two targets are presented farther apart in time or relative to when the first target (T1) can be ignored. This effect is known as the attentional blink (AB). An additional T2 accuracy deficit is observed if T1 and T2 are identical or highly similar on a task-relevant dimension. This effect is known as repetition blindness (RB). For both AB and RB, targets are typically imbedded in rapid serial visual presentation (RSVP) streams and the dual-task attention cost lasts approximately half a second. Given the high degree of superficial similarity, AB and RB are often considered to be related phenomena. Although research thus far has suggested that both phenomena reflect limits of the attentional system and how attention is allocated when needing to organize stimuli for entrance into awareness, these two phenomena are dissociable; RB is not simply an enhanced AB. Furthermore, investigations of AB and RB have taken quite different courses over the last two decades. The AB has been investigated extensively with a variety of experimental, behavioral, neurophysiological, and clinical approaches, and has become widely used as a paradigm of convenience with which to study other effects. In contrast, studies of RB have tended to manipulate the nature of the target information to understand the level of representation that supports RB. WIREs Cogni Sci 2011 2 336-344 DOI: 10.1002/wcs.129 For further resources related to this article, please visit the WIREs website.

Mouse models of neurodegenerative diseases: criteria and general methodology

The major symptom of Alzheimer's disease is rapidly progressing dementia, coinciding with the formation of amyloid and tau deposits in the central nervous system, and neuronal death. At present familial cases of dementias provide the most promising foundation for modelling neurodegeneration. We describe the mnemonic and other major behavioral symptoms of tauopathies, briefly outline the genetics underlying familiar cases and discuss the arising implications for modelling the disease in mostly transgenic mouse lines. We then depict to what degree the most recent mouse models replicate pathological and cognitive characteristics observed in patients.There is no universally valid behavioral test battery to evaluate mouse models. The selection of individual tests depends on the behavioral and/or memory system in focus, the type of a model and how well it replicates the pathology of a disease and the amount of control over the genetic background of the mouse model. However it is possible to provide guidelines and criteria for modelling the neurodegeneration, setting up the experiments and choosing relevant tests. One should not adopt a "one (trans)gene, one disease" interpretation, but should try to understand how the mouse genome copes with the protein expression of the transgene in question. Further, it is not possible to recommend some mouse models over others since each model is valuable within its own constraints, and the way experiments are performed often reflects the idiosyncratic reality of specific laboratories. Our purpose is to improve bridging molecular and behavioural approaches in translational research.

Staged decline of visual processing capacity in mild cognitive impairment and Alzheimer's disease

Visual information intake was assessed with a whole-report task in patients with probable Alzheimer's disease (AD), mild cognitive impairment (MCI), and healthy elderly control subjects. Based on a theory of visual attention (TVA), four parameters were derived characterising different aspects of visual processing capacity: perceptual threshold, iconic memory, processing speed, and visual short-term memory (VSTM) storage capacity. Results indicated increased perceptual thresholds in MCI, and an additional decline in processing speed and VSTM storage capacity in AD. Cholinomimetic medication had beneficial effects on processing speed in AD patients. Perceptual thresholds were associated with disease duration, but not with cognitive measures, while the reverse was true for speed and VSTM measures. These results reveal a staged pattern of deficits affecting pre-attentive visual processing in MCI, and attentive processing in AD. It is compatible with the amyloid cascade hypothesis and suggests that impaired visual processing is a pathological feature present already at the MCI stage and might represent a distinct marker of upcoming AD independently from memory deficits.

White matter integrity linked to functional impairments in aging and early Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is associated with changes in cerebral white matter (WM), but the functional significance of such findings is not yet established. We hypothesized that diffusion tensor imaging (DTI) might reveal links between regional WM changes and specific neuropsychologically and psychophysically defined impairments in early AD.

METHODS

Older adult control subjects (OA, n = 18) and mildly impaired AD patients (n = 14) underwent neuropsychological and visual perceptual testing along with DTI of cerebral WM. DTI yielded factional anisotropy (FA) and mean diffusivity (D) maps for nine regions of interest in three brain regions that were then compared with the performance measures.

RESULTS

AD patients exhibited nonsignificant trends toward lower FAs in the posterior region's callosal and subcortical regions of interest. However, posterior callosal FA was significantly correlated with verbal fluency and figural memory impairments, whereas posterior subcortical FA was correlated with delayed verbal memory, figural memory, and optic flow perceptual impairments.

CONCLUSIONS

WM changes in early AD are concentrated in posterior cerebral areas, with distributions that correspond to specific functional impairments. DTI can be used to assess regional pathology related to individual's deficits in early AD.

Effects of addiction-associated and affective stimuli on the attentional blink in a sample of abstinent opiate dependent patients

The attentional blink reveals the limits of the brain's ability in information processing. It has been extensively studied in people with neurological and psychiatric disturbances to explore the temporal characteristics of information processing and examine attention deficits. The aim of the present study is to examine the attentional blink in abstinent opiate dependent patients (AODPs). Also, we planned to study whether addiction-associated and affective stimuli can influence the attentional blink in AODPs. A dual-target rapid serial visual presentation test (RSVP) was used in the present study. The second target consisted of three kinds of stimuli: neutral, addiction-associated and negative. We found that there was an exaggerated attentional blink in AODPs. It suggested that there were the deficits of information processing and attention in AODPs. Addiction-associated stimuli reduced the attentional blink in AODPs, suggesting addiction-associated information were selected by the brain for attentive and perceptual processing. In addition, affective effects on the attentional blink in AODPs were not in the similar level to those in controls.