Executive Dysfunction in MCI: Subtype or Early Symptom

Mild cognitive impairment (MCI) may take several forms, and amnestic MCI (aMCI) has been recognized as an early stage of Alzheimer's Disease (AD). Impairment in executive functions including attention (eMCI) may be indicative of several neurodegenerative conditions. Executive impairment is frequently found in aMCI, it is significant for prognosis, and patients with eMCI may go on to develop AD. Recent studies have found changes in white matter integrity in patients with eMCI to be more sensitive than measures of cortical atrophy. Studies of genetic high-risk groups using sensitive cognitive neuroscience paradigms indicate that changes in executive function may be a cognitive marker useful for tracking development in an AD pathophysiological process

Hemispheric asymmetry in visual discrimination and memory: ERP evidence for the spatial frequency hypothesis

Event related potentials (ERPs) were recorded during delayed discrimination of simple spatial frequency gratings in the high and low frequency bands. Analyses of the waveforms N170, P220, N310, P400, and slow wave (SW) indicated significant and regionally specific interaction of spatial frequency and hemisphere for N170 amplitude. This interaction was independent of memory conditions, and appeared to be in the opposite direction of what is predicted by the spatial frequency model of hemispheric asymmetry. Additional interactions between spatial frequency and hemisphere were observed for N310 in the encoding process (reference stimulus) and for SW in the retrieval process (test stimulus). The general hypothesis of an interaction of spatial frequency and hemisphere in visual cognition is supported, but the findings indicate caution in interpreting an increase in physiological measures as an indication of more efficient brain processing. Moreover, several stages of information processing may contribute to the asymmetry observed in behavioral studies, and hemispheric balance may change dynamically during the time course of processing

Brain regions involved in spatial frequency discrimination: evidence from fMRI

The cortical areas underlying successive spatial-frequency discrimination were explored using functional magnetic resonance imaging (fMRI). In a steady-state, block-design paradigm, 12 subjects viewed a single fixation cross during a rest period, followed by an activation period consisting of the presentation of horizontal (distractors) and vertical (targets) sinewave gratings. Two tasks were performed: in the control task, subjects pressed a button after the second vertical grating was presented within each trial; in the discrimination task, subjects decided which target grating had the higher spatial frequency. Post-processing consisted of off-line image registration to correct for head motion, spatial and temporal smoothing, and cross-correlation between each voxel time course and a phase-shifted stimulus time profile. The results indicate that striate, extrastriate, parietal, and prefrontal areas show significant BOLD (blood oxygen level dependent) effects during both discrimination and control tasks, with consistently higher activity levels in the discrimination task

Rāma: Helt, gud og politisk symbol

The article “Rāma: Hero, God and Political Symbol” outlines three different ways in which the Rāma-figure has been used in Indian history. As a basis, hermeneutical problems related to the critical interpretation of the Rāmāyana are briefly discussed, and the main story of the epic is outlined.In the core parts of the Rāmāyana epic, Rāma can still be recognised as representing the ethos of the warrior-class (ksatrīya-varna). The Rāma of this historical phase, approximately covering the era between 400 B.C. and the Gupta era (320-500 A.D.), incarnates the dharma of the ksatrīya; which implies protection of the just, combat against the powers of chaos, and the maintaining of the norms and the social divisions of society. When the classical Rāmāyana finds its basic form during the Gupta period, under the hands of Vaisnavite Brahmins, Rāma is extolled as being an incarnation of the supreme god Visnu. As such, Rāma is God, having incarnated on earth to save mankind from evil and the universe from the powers of chaos. Brahminical notions of purity are now considered essential to the Rāma-figure, with the effect that the conclusion of the original story has to be rewritten so that Rāma does not take his abducted - and thus defiled - wife Sītā back after she has been liberated from the evil rāksasa Rāvana. The ksatrīya-Rāma has thus been replaced with a vaisnava-Rāma, a Rāma incarnating a different set of values.As a parallel to this historical development, the article proceeds to outline how, during the last twenty years, Rāma has become a symbol of a new Hindu-nationalistic consciousness. In this context, Rāma is imagined as a warrior ready to fight for the assertion of “hinduness” (hindutva), in opposition to what is considered a century’s old suppression carried out by Muslim rulers, the British Raj and the independent, secular Indian state. Political campaigns and the conflict around the Babri-masjid in Ayodhyā, are highlighted in order to show how Rāma, through the stratagems of the Hindu nationalistic movement, has recently emerged as a symbol of an aggressive Hindu consciousness. The article stresses that the main presuppositions for the Hindu nationalistic use of Rāma are to be found in the political culture of modern India, which takes its outset in forms of organisation and concepts of political thought imported by the British. There is thus nothing essentially and eternally “Indian” about the present Hindu nationalism.Finally, the article notes that the very fact that an ancient Indian symbol in the Hindu nationalistic context is revitalised and transformed to fit the circumstances of the present, reflects the inherent power of what we generally call “Hinduism” (a modern term originally coined by European scholars). As was the case when the original warrior-hero Rāma in the Gupta era was made into an incarnation of the supreme God, due to the mode of the religious sentiments of the time and the interest of certain classes, Rāma has lately become a political symbol, due to the mode of the political sentiments in the India of the present and the interests of certain classes. Again, the complex blend of change and continuity, so characteristic of “Hinduism”, leaps to mind

Electrophysiological localization of brain regions involved in perceptual memory

Event-related potentials (ERP) were recorded during perceptual discrimination and short-term memory, varying the interstimulus interval (1–10 s) in delayed spatial frequency discrimination. Accuracy of discrimination remained unimpaired across this time interval, but choice reaction times increased. A brain source localization (BESA) model showed that the activity of the parietal and right temporal sources increased with long retention intervals in a sequential activation pattern where a long-latency component of the parietal source specific to the memory condition was observed, the latency of which matched a memory-related increase in choice reaction times in the cognitive task. It is suggested that the temporal sources are involved in encoding and storage of visual information, and the parietal source is involved in memory retrieval

Neurogenetic Effects on Cognition in Aging Brains: A Window of Opportunity for Intervention?

Knowledge of genetic influences on cognitive aging can constrain and guide interventions aimed at limiting age-related cognitive decline in older adults. Progress in understanding the neural basis of cognitive aging also requires a better understanding of the neurogenetics of cognition. This selective review article describes studies aimed at deriving specific neurogenetic information from three parallel and interrelated phenotype-based approaches: psychometric constructs, cognitive neuroscience-based processing measures, and brain imaging morphometric data. Developments in newer genetic analysis tools, including genome wide association, are also described. In particular, we focus on models for establishing genotype–phenotype associations within an explanatory framework linking molecular, brain, and cognitive levels of analysis. Such multiple-phenotype approaches indicate that individual variation in genes central to maintaining synaptic integrity, neurotransmitter function, and synaptic plasticity are important in affecting age-related changes in brain structure and cognition. Investigating phenotypes at multiple levels is recommended as a means to advance understanding of the neural impact of genetic variants relevant to cognitive aging. Further knowledge regarding the mechanisms of interaction between genetic and preventative procedures will in turn help in understanding the ameliorative effect of various experiential and lifestyle factors on age-related cognitive decline

Thalamic pathology and memory loss in early Alzheimer’s disease: moving the focus from the medial temporal lobe to Papez circuit

It is widely assumed that incipient protein pathology in the medial temporal lobe instigates the loss of episodic memory in Alzheimer’s disease, one of the earliest cognitive deficits in this type of dementia. Within this region, the hippocampus is seen as the most vital for episodic memory. Consequently, research into the causes of memory loss in Alzheimer’s disease continues to centre on hippocampal dysfunction and how disease-modifying therapies in this region can potentially alleviate memory symptomology. The present review questions this entrenched notion by bringing together findings from post-mortem studies, non-invasive imaging (including studies of presymptomatic, at-risk cases) and genetically modified animal models. The combined evidence indicates that the loss of episodic memory in early Alzheimer’s disease reflects much wider neurodegeneration in an extended mnemonic system (Papez circuit), which critically involves the limbic thalamus. Within this system, the anterior thalamic nuclei are prominent, both for their vital contributions to episodic memory and for how these same nuclei appear vulnerable in prodromal Alzheimer’s disease. As thalamic abnormalities occur in some of the earliest stages of the disease, the idea that such changes are merely secondary to medial temporal lobe dysfunctions is challenged. This alternate view is further strengthened by the interdependent relationship between the anterior thalamic nuclei and retrosplenial cortex, given how dysfunctions in the latter cortical area provide some of the earliest in vivo imaging evidence of prodromal Alzheimer’s disease. Appreciating the importance of the anterior thalamic nuclei for memory and attention provides a more balanced understanding of Alzheimer’s disease. Furthermore, this refocus on the limbic thalamus, as well as the rest of Papez circuit, would have significant implications for the diagnostics, modelling, and experimental treatment of cognitive symptoms in Alzheimer’s disease