Voyko Kavcic

Spatial disorientation in Alzheimer’s disease The remembrance of things passed

Background: Patients with Alzheimer’s disease (AD) and many older adults become lost even in familiar surroundings. This is commonly attributed to memory impairment, but it may reflect impaired spatial cognition. Methods: The authors examined the role of memory, perceptual, and cognitive mechanisms in spatial disorientation by comparing the performance of normal young (YN), middle-aged (MA), older adult (OA), and AD subjects on neuropsychological and spatial orientation tests. Results: The tendency to become lost is shared by almost all patients with AD (93%) and some OA subjects (38%). This impairment is not related to memory impairment. Instead, it reflects an inability to link recognized scenes with locations in the environment. Conclusions: Spatial disorientation reflects the impaired linking of landmarks and routes that should be assessed in conjunction with routine memory testing in elderly patients.

Neurophysiologic analyses of low- and high-level visual processing in Alzheimer disease

Objective: We developed visual motion evoked potential (EP) measures related to navigational impairment in Alzheimer disease (AD) and have now applied these methods to explore the role of elementary perceptual and attentional mechanisms mediating these effects. Methods: Older adult (OA) control subjects and AD patients underwent visual motion perceptual testing, attentional performance monitoring, and basic neuropsychological and visual assessments. We recorded stationary pattern onset and visual motion onset EPs as well as behavioral event–related potentials during centered visual fixation. Results: Psychophysical assessment demonstrated visual motion perceptual impairments in patients with AD, half of whom also showed low sensitivity in the attentional task. The low sensitivity AD patients had small pattern onset and absent motion onset EPs, whereas the high sensitivity AD patients had large pattern onset EPs and normal motion onset EPs. Conclusions: We conclude that visual evoked potentials (EPs) are abnormal in all patients with Alzheimer disease (AD): Those with small pattern and motion onset EPs may have greater AD pathology in visual cortex, whereas those with larger pattern onset EPs may have greater AD pathology in higher centers. These findings highlight the utility of visual EPs in distinguishing between syndromic variants of AD associated with particular patterns of functional decline.

White Matter Integrity Linked To Functional Impairments in Aging and Early Alzheimer’s Disease

Alzheimers 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.

The brain in micro- and hypergravity: The effects of changing gravity on the brain electrocortical activity

Abstract Understanding the effects of increased and decreased gravity on central nervous system is essential for developing proper physical and cognitive countermeasures to assure safe and effective space missions and human survival in space. This short review covers the available literature on the brain electrocortical activity effects of decreased and increased gravitational force comparing to the 1g Earth conditions. Among all neuroimaging methods such as functional magnetic resonance imaging (fMRI), positron-emission tomography (PET), diffusion tensor imaging (DTI), the electroencephalography (EEG) was found to be suitable method to monitor brain electrocortical activity in the extreme environments. Due to complexity and high cost of space flight missions, ground-based models have been employed to simulate microgravity effects on human body. Surprisingly, there is very limited number of publications reporting gravity-dependent EEG spectral changes. With increased gravity there are initially increased EEG activity in higher frequencies and at around 4g appears loss of consciousness with accompanying slowing of EEG due to hypoxia. In microgravity, the most prevalent changes in EEG are faster frequencies such as alpha and beta. The results from simulated microgravity (bed rest) are pointing to changes in theta and alpha, representing signs of cortical inhibition. The changes in EEG activity in space flight are attributed to a decreased sensorimotor input while in parabolic flights short and fast transitions from hyper to microgravity presumably reflect lower arousal levels and emotional processes in microgravity. Thus, based on limited research about gravity-related changes in EEG from different environments it is difficult to draw any unequivocal conclusions. Additional systematic studies about electrocortical activity in space and parabolic flights, as well as longer bed rest studies are needed in order to advance knowledge about brain functioning in extreme conditions such as space flights.

Motion-onset visual evoked potentials predict performance during a global direction discrimination task.

The relationship between cognitive processing stages and event-related potential components has been extensively researched for single components, but even the simplest task comprises multiple electrophysiological and cognitive components. Here we examined the relationship between behavioral measures and several visual evoked potentials (VEPs) related to global motion onset during a visual motion discrimination task. In addition to reaction time and accuracy, the EZ diffusion model was used to characterize elements of the decision process. Results showed that latencies, but not amplitudes, from three VEP components reliably predicted about 40% of the variance in reaction times for motion discrimination. These included the latency from stimulus motion onset to N2 onset, the latency from N2 onset to N2 peak, and the latency from the N2 peak to the peak of a late positive potential. These latencies were also able to predict the rate of information accumulation during the decision process and the duration of non-decision processes, but not the observers threshold (boundary) for making a response. This pattern of results is consistent with an interpretation of these three latencies as reflecting a non-specific visual perceptual process, a motion-specific process, and a decision process, respectively. The relationship between the earliest interval and drift rate estimated with the EZ model also supports the notion that early perceptual processing might be a constituent part of the decision process itself.

Role of inter-hemispheric transfer in generating visual evoked potentials in V1-damaged brain hemispheres

Partial cortical blindness is a visual deficit caused by unilateral damage to the primary visual cortex, a condition previously considered beyond hopes of rehabilitation. However, recent data demonstrate that patients may recover both simple and global motion discrimination following intensive training in their blind field. The present experiments characterized motion-induced neural activity of cortically blind (CB) subjects prior to the onset of visual rehabilitation. This was done to provide information about visual processing capabilities available to mediate training-induced visual improvements. Visual Evoked Potentials (VEPs) were recorded from two experimental groups consisting of 9 CB subjects and 9 age-matched, visually-intact controls. VEPs were collected following lateralized stimulus presentation to each of the 4 visual field quadrants. VEP waveforms were examined for both stimulus-onset (SO) and motion-onset (MO) related components in postero-lateral electrodes. While stimulus presentation to intact regions of the visual field elicited normal SO-P1, SO-N1, SO-P2 and MO-N2 amplitudes and latencies in contralateral brain regions of CB subjects, these components were not observed contralateral to stimulus presentation in blind quadrants of the visual field. In damaged brain hemispheres, SO-VEPs were only recorded following stimulus presentation to intact visual field quadrants, via inter-hemispheric transfer. MO-VEPs were only recorded from damaged left brain hemispheres, possibly reflecting a native left/right asymmetry in inter-hemispheric connections. The present findings suggest that damaged brain hemispheres contain areas capable of responding to visual stimulation. However, in the absence of training or rehabilitation, these areas only generate detectable VEPs in response to stimulation of the intact hemifield of vision.

Hemispheric interactions during a face-word Stroop-analog task

A Stroop-analog task with faces and words was developed to investigate intrahemispheric and interhemispheric Stroop effects (SEs). Lateralized faces and words were used in an attempt to invoke right- and left-hemispheric specialization, respectively. A prototypical male face, female face, and baby face and the corresponding words man, woman, and baby were presented as congruent or incongruent face-word pairs either to the same visual field (i.e., unilateral presentations) or to separate visual fields (i.e., bilateral presentations). Bidirectional SEs were found. Word distractors interfered with the identification of face targets, and, somewhat surprisingly, an even greater SE was obtained when words were the target and faces were ignored. Laterality effects were most pronounced for bilateral trials, whereby the SE was larger for right-hemisphere than for left-hemisphere target presentations, irrespective of type of target. This finding suggests that the left hemisphere is generally better shielded than the right from interhemispheric interference effects.

Computerized cognitive training during physical inactivity improves executive functioning in older adults

ABSTRACT The hippocampus is closely tied to spatial navigation, a central component in cognitive functioning, and critically involved in age-associated cognitive decline and dementia. This study evaluated a novel, cognitive computerized spatial navigation training (CSNT) program targeting the hippocampus, with expectation of mitigating possible cognitive decline with bed rest (BR). During a 14-day BR study with 16 healthy, older men (mean age = 60 ± 3, range = 55–65 years), half received CSNT for 12 days in 50-min sessions and half were controls (watching documentaries). This design uniquely controlled diet, sleep, and other personal and environmental activities. Although there were no cognitive declines in controls post-BR, CSNT participants demonstrated significant increases in executive/attention ability and processing speed, and continued spatial navigation testing showed improvement to 400 days post-BR. This intervention may prove useful to mitigate cognitive declines known to occur in long periods of immobilization and could have broader implications in protecting against age-related cognitive decline.

Computerized spatial navigation training during 14 days of bed rest in healthy older adult men: Effect on gait performance.

Prolonged physical inactivity or bed rest (BR) due to illness or other factors can result in significant declines in physical health and even cognitive functions. Based on random selection, 7 healthy older adult men received computerized spatial navigation training, while 8 served as active controls during 14-day BR. Greater post-BR declines were seen in normal and complex (dual-task) walking for the control as compared to intervention group, suggesting that computerized spatial navigation training can successfully moderate detrimental BR effects. Findings underline the generalization of cognitive-based intervention to the motor domain and potentially support their use to supplement BR interventions (e.g., exercise and nutrition).

Aging effects on visual evoked potentials (VEPs) for motion direction discrimination

Age-related declines in motion perception have been well documented. We investigated the impact of age on electrophysiological correlates of motion perception, namely the P1 and N2 components of motion onset visual evoked potentials (MO-VEPs). Additionally, we used a model of response times based on the diffusion model to pinpoint the cognitive processes affected by aging. Twelve healthy adults (age <55 years) and 19 elderly (age >55 years) performed a motion direction discrimination task during EEG recording. Behaviorally, younger and older participants had similar, high accuracy rates--98% correct, but older adults exhibited 85 ms longer response times. Fitting behavioral results with a diffusion model revealed differences between young adults and elderly in non-decision time, which we argue reflects an early perceptual stage. Electrophysiologically, aging effects were present at MO-VEPs P1 and N2 components at the posterior sites. For the P1 component, older as compared to younger adults showed greater topographical voltage distribution. For the N2 component of elderly as compared to young adults we found delayed onsets and diminished amplitudes. We did not find any significant correlations between behavioral and MO-VEP measures. However, regression analysis showed that N2 amplitude and latency were significant age predictors. Overall, our results indicate that in motion perception, age-related changes occur in early stages of visual processing, most likely in striate and extrastriate visual cortices.