Positive Evidence against Human Hippocampal Involvement in Working Memory Maintenance of Familiar StimuliEric Zarahn, Brian C. Rakitin, Diane Abela, Joseph Flynn & Yaakov Stern
Subjects (n = 40) performed a delayed item recognition task for visually presented letters with three set sizes (1, 3 or 6 letters). Accuracy was close to ceiling at all set sizes, so we took set size as a proxy for WM load (i.e. the amount of information being maintained in WM). Functional magnetic resonance imaging (fMRI) signal associated with the delay period increased in a nearly linear fashion with WM load in the left...
OBJECTIVE: To determine whether specific cognitive deficits can predict the progression of Alzheimer disease (AD). METHODS: Two hundred fifty-two patients with AD enrolled in the Predictors Study were followed at 6-month intervals for up to 4.5 years with neurologic, cognitive, and psychiatric examinations. Neuropsychological functions were assessed by the Modified Mini-Mental State Examination (mMMSE). Items of mMMSE were divided into five cognitive domains: temporospatial orientation, short-term memory, long-term memory, language, and visuoconstructive functions. Loss of...
Depressive Symptoms in Alzheimer's Disease: Natural Course and Temporal Relation to Function and Cognitive StatusRoee Holtzer, Nikolaos Scarmeas, Domonick Wegesin, Marilyn Albert, Jason Brandt, Bruno Dubois, Georgios Hadjigeorgiou & Yaakov Stern
OBJECTIVES: To examine the natural course of depressive symptoms in patients with probable Alzheimer's disease (AD), specifically, the temporal relationship between depressive symptoms, function, and cognitive status. DESIGN: Multicenter cohort study with follow-up of up to 14 years. SETTING: Patients from the two Multicenter Study of Predictors of Disease Course in Alzheimer's Disease (Predictors Study) cohorts were recruited at five sites in the United States and Europe. PARTICIPANTS: Patients diagnosed with probable AD (n=536) enrolled...
OBJECTIVE: To examine whether the presence of motor signs has predictive value for important outcomes in Alzheimer disease (AD). METHODS: A total of 533 patients with AD at early stages (mean Folstein Mini-Mental State Examination [MMSE] 21/30 at entry) were recruited and followed semiannually for up to 13.1 years (mean 3) in five University-based AD centers in the United States and European Union. Four outcomes, assessed every 6 months, were used in Cox models: cognitive...
In lateral quantum dots, the combined effect of both Dresselhaus and Bychkov-Rashba spin-orbit coupling is equivalent to an effective magnetic field ±BSO which has the opposite sign for sz=±1/2 spin electrons. When the external magnetic field is perpendicular to the planar structure, the field BSO generates an additional splitting for electron states as compared to the spin splitting in the in-plane field orientation. The anisotropy of spin splitting has been measured and then analyzed in...
With noninvasive methods, we investigate ground and excited states of a lateral quantum dot. Charge detection via a quantum point contact is used to map the dot dynamics in a regime where the current through the dot is too low for transport measurements. In this way we investigate and compare the tunneling rates from the dot to source and drain. We find a symmetry line on which the tunneling rates to both leads are equal....
We demonstrate electron redistribution caused by magnetic field on a single quantum dot measured by means of a quantum point contact as noninvasive detector. Our device, which is fabricated by local anodic oxidation, allows us to control independently the quantum point contact and all tunneling barriers of the quantum dot. Thus we are able to measure both the change of the quantum dot charge and also changes of the electron configuration at constant number of...
Direct measurements of the spin and valley splittings in the magnetization of a SiSiGe quantum well in tilted magnetic fieldsM.A. Wilde, M. Rhode, C. Heyn, D. Heitmann, D. Grundler, U. Zeitler, F. Schäffler & Rolf J. Haug
We present de Haas-van Alphen (dHvA) measurements on high-mobility two-dimensional electron systems formed in modulation-doped SiSiGe (100) quantum wells and demonstrate directly the manifestation of the valley splitting in the magnetization. We resolve sawtoothlike magnetization oscillations at even filling factors which reflect the Landau quantization and the spin splitting of Landau levels in the electronic energy spectrum. At odd filling factors we observe the lifting of the valley degeneracy in Si at high magnetic field....
Photoluminescence emission spectra of self-assembled single InAs/AlAs quantum dots with variable size reveal typical sharp lines below 1.8 eV, corresponding to transitions between fully confined states. Above this energy the sharp peaks disappear due to the Γ-X scattering of conduction electrons. Excitation spectra of the biexciton line in single quantum dots show marked maxima at the optical-phonon frequency of the quantum dot and at its first overtone. The quantum dot phonon energy observed is 31...
We have measured the conductivity σxx of GaAs GaAlAs Corbino devices under nonequilibrium conditions in the quantum Hall regime at low frequencies from dc up to 10 kHz. At very low frequencies up to 10-20 Hz, σxx shows a steep decrease from its dc value towards a reduced saturation value. Measurements of the temperature dependence of σxx from 70 mK to 4.2 K revealed a dominance of a conductivity with a temperature dependence σxx ∼exp...
By single-electron tunneling spectroscopy we investigate the difference in spin splitting of single-electron resonances in a double-barrier structure subjected to a magnetic field perpendicular (Δ⊥) and parallel (Δ∥) to the plane of quantum well. The observed anisotropy of spin splitting is interpreted within a model of spin-orbit coupling in quantum dots. © 2005 American Institute of Physics.
Quantum Hall samples with Corbino geometry show an enhanced hysteresis of the I-V curves near the breakdown of the Quantum Hall effect at low AC frequencies. We explain this finding within a hot-electron model by an assumed reduction of the subcritical conductivity σxx (under non-equilibrium conditions) with frequency. In this study, we present measurements of σxx as a function of the frequency on various samples. The observed drop of the subcritical σxx with frequency is...
The activation gap Δ of the fractional quantum Hall states at constant fillings v = 2/3 and 2/5 has been measured as a function of the perpendicular magnetic field B. A linear dependence of Δ on B is observed while approaching the spin polarization transition, yielding a direct measurement of the g-factor of Composite Fermions. © 2005 American Institute of Physics.
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