21 research outputs found
The acetylcholine index: an electroencephalographic marker of cholinergic activity in the living human brain applied to Alzheimer's disease and other dementias.
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This article is open access.The cholinergic hypothesis is well established and has led to the development of pharmacological treatments for Alzheimer's disease (AD). However, there has previously been no physiological means of monitoring cholinergic activity in vivo.An electroencephalography (EEG)-based acetylcholine (Ach) index reflecting the cholinergic activity in the brain was developed using data from a scopolamine challenge study. The applicability of the Ach index was examined in an elderly population of healthy controls and patients suffering from various causes of cognitive decline.The Ach index showed a strong reduction in the severe stages of AD dementia. A high correlation was demonstrated between the Ach index and cognitive function. The index was reduced in patients with mild cognitive impairment and prodromal AD, indicating a decreased cholinergic activity. When considering the distribution of the Ach index in a population of healthy elderly subjects, an age-related threshold was revealed, beyond which there is a general decline in cholinergic activity.The EEG-based Ach index provides, for the first time, a physiological means of monitoring the cholinergic activity in the human brain in vivo. This has great potential for aiding diagnosis and patient stratification as well as for monitoring disease progression and treatment response.Icelandic Technology Development Fund/051221006
Icelandic Technology Development Fund/08120600
Contact resistance of quantum tubes
We consider the conductance of a quantum tube connected to a metallic
contact. The number of angular momentum states that the tube can support
depends on the strength of the radial confinement. We calculate the
transmission coefficients which yield the conductance via the Landauer formula.
We relate our results to armchair carbon nanotubes embedded in a metal. For Al
and Au contacts and tubes with a realistic radial confinement we find that the
transmission can be close to unity corresponding to a contact resistance close
to h/2e^2 per band at the Fermi level in the carbon nanotube.Comment: 13 pages including 5 figures. Accepted for publication in
Superlattices and Microstructures. (stylefile included
Electroencephalography as a clinical tool for diagnosing and monitoring attention deficit hyperactivity disorder: a cross-sectional study.
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This article is open access.The aim of this study was to develop and test, for the first time, a multivariate diagnostic classifier of attention deficit hyperactivity disorder (ADHD) based on EEG coherence measures and chronological age.The participants were recruited in two specialised centres and three schools in Reykjavik.The data are from a large cross-sectional cohort of 310 patients with ADHD and 351 controls, covering an age range from 5.8 to 14â
years. ADHD was diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders fourth edition (DSM-IV) criteria using the K-SADS-PL semistructured interview. Participants in the control group were reported to be free of any mental or developmental disorders by their parents and had a score of less than 1.5 SDs above the age-appropriate norm on the ADHD Rating Scale-IV. Other than moderate or severe intellectual disability, no additional exclusion criteria were applied in order that the cohort reflected the typical cross section of patients with ADHD.Diagnostic classifiers were developed using statistical pattern recognition for the entire age range and for specific age ranges and were tested using cross-validation and by application to a separate cohort of recordings not used in the development process. The age-specific classification approach was more accurate (76% accuracy in the independent test cohort; 81% cross-validation accuracy) than the age-independent version (76%; 73%). Chronological age was found to be an important classification feature.The novel application of EEG-based classification methods presented here can offer significant benefit to the clinician by improving both the accuracy of initial diagnosis and ongoing monitoring of children and adolescents with ADHD. The most accurate possible diagnosis at a single point in time can be obtained by the age-specific classifiers, but the age-independent classifiers are also useful as they enable longitudinal monitoring of brain function.Icelandic Technology Development Fund 071201007
Landspitali University Hospital Research Fun
Density Matrix Functional Calculations for Matter in Strong Magnetic Fields: I. Atomic Properties
We report on a numerical study of the density matrix functional introduced by
Lieb, Solovej and Yngvason for the investigation of heavy atoms in high
magnetic fields. This functional describes {\em exactly} the quantum mechanical
ground state of atoms and ions in the limit when the nuclear charge and the
electron number tend to infinity with fixed, and the magnetic field
tends to infinity in such a way that . We have
calculated electronic density profiles and ground state energies for values of
the parameters that prevail on neutron star surfaces and compared them with
results obtained by other methods. For iron at G the ground state
energy differs by less than 2 \% from the Hartree-Fock value. We have also
studied the maximal negative ionization of heavy atoms in this model at various
field strengths. In contrast to Thomas-Fermi type theories atoms can bind
excess negative charge in the density matrix model. For iron at G
the maximal excess charge in this model corresponds to about one electron.Comment: Revtex, 13 pages with 6 eps figures include
Linear optical absorption spectra of mesoscopic structures in intense THz fields: free particle properties
We theoretically study the effect of THz radiation on the linear optical
absorption spectra of semiconductor structures. A general theoretical
framework, based on non-equilibrium Green functions, is formulated, and applied
to the calculation of linear optical absorption spectrum for several
non-equilibrium mesoscopic structures. We show that a blue-shift occurs and
sidebands appear in bulk-like structures, i.e., the dynamical Franz-Keldysh
effect [A.-P. Jauho and K. Johnsen, Phys. Rev. Lett. 76, 4576 (1996)]. An
analytic calculation leads to the prediction that in the case of superlattices
distinct stable steps appear in the absorption spectrum when conditions for
dynamical localization are met.Comment: 13 Pages, RevTex using epsf to include 8 ps figures. Submitted to
Phys. Rev. B (3 April 97
Understanding the nature of face processing in early autism: a prospective study
4AbstractDimensional approaches to psychopathology interrogate the core neurocognitive domains interactingat the individual level to shape diagnostic symptoms. Embedding this approach in prospective longitudinal studies couldtransform our understanding of the mechanisms underlying neurodevelopmental disorders. Such designs require us to move beyond traditional group comparisons and determine which domain-specific alterations apply at the level of the individual, and whether they vary across distinct phenotypic subgroups. As a proof of principle, this studyexamineshow the domain of face processingcontributes to the emergenceof Autism Spectrum Disorder (ASD). We used an event-related potentials (ERPs) task in a cohort of 8-month-oldinfants with (n=148) and without (n=68) an older sibling withASD, andcombined traditional case-control comparisonswith machine-learningtechniques for prediction of social traits and ASD diagnosisat 36 months,and Bayesian hierarchical clustering for stratification into subgroups. Abroad profile of alterations in the time-course of neural processing of faces in infancy was predictive oflaterASD, with a strong convergence in ERP features predicting social traits and diagnosis.We identified two main subgroups in ASD,defined by distinct patternsof neural responsestofaces,which differed on latersensory sensitivity. Taken together, our findings suggest that individual differences between infantscontribute to the diffuse pattern of alterations predictive of ASD in the first year of life. Moving from group-level comparisons to pattern recognition and stratification can help to understand and reduce heterogeneity in clinical cohorts, and improve our understanding of the mechanisms that lead to later neurodevelopmental outcomes
What Electrophysiology Tells Us About Alzheimerâs Disease::A Window into the Synchronization and Connectivity of Brain Neurons
Electrophysiology provides a real-time readout of neural functions and network capability in different brain states, on temporal (fractions of milliseconds) and spatial (micro, meso, and macro) scales unmet by other methodologies. However, current international guidelines do not endorse the use of electroencephalographic (EEG)/magnetoencephalographic (MEG) biomarkers in clinical trials performed in patients with Alzheimerâs disease (AD), despite a surge in recent validated evidence. This Position Paper of the ISTAART Electrophysiology Professional Interest Area endorses consolidated and translational electrophysiological techniques applied to both experimental animal models of AD and patients, to probe the effects of AD neuropathology (i.e., brain amyloidosis, tauopathy, and neurodegeneration) on neurophysiological mechanisms underpinning neural excitation/inhibition and neurotransmission as well as brain network dynamics, synchronization, and functional connectivity reflecting thalamocortical and cortico-cortical residual capacity. Converging evidence shows relationships between abnormalities in EEG/MEG markers and cognitive deficits in groups of AD patients at different disease stages. The supporting evidence for the application of electrophysiology in AD clinical research as well as drug discovery pathways warrants an international initiative to include the use of EEG/MEG biomarkers in the main multicentric projects planned in AD patients, to produce conclusive findings challenging the present regulatory requirements and guidelines for AD studies