A previously proposed model for memory based on neurophysiological considerations is reviewed. We assume that (a) nervous system activity is usefully represented as the set of simultaneous individual neuron activities in a group of neurons; (b) different memory traces make use of the same synapses; and (c) synapses associate two patterns of neural activity by incrementing synaptic connectivity proportionally to the product of pre-and postsynaptic activity, forming a matrix of synaptic connectivities. We extend this model by (a) introducing positive feedback of a set of neurons onto itself and (b) allowing the individual neurons to saturate. A hybrid model, partly analog and partly binary, arises. The system has certain characteristics reminiscent of analysis by distinctive features. Next, we apply the model to "categorical perception." Finally, we discuss probability learning. The model can predict overshooting, recency data, and probabilities occurring in systems with more than two events with reasonably good accuracy. In the beginner's mind there are many possibilities, but in the expert's there are few.
Proton magnetic resonance spectroscopy (1H-MRS) allows major metabolites to be measured noninvasively in defined regions of the living brain, and can detect biochemical abnormalities where conventional structural imaging appears normal. MRS can be performed in 10 min as part of a clinical MRI examination. Biochemical abnormalities in Alzheimer's Disease (AD), vascular dementia (VaD) and other primary degenerative dementias have been investigated using MRS. Characteristic and consistent abnormalities in AD are decreased N-acetyl aspartate (NAA) and elevated myo-inositol (mI) in the mesial temporal and parieto-occipital cortex. These are thought to represent neuronal loss/dysfunction and gliosis, in anatomic distributions which reflect early pathological involvement and atrophy patterns in AD. Less consistent disturbances of glutamine and glutamate (Glx) and choline-containing compounds (Cho) have also been reported. Similar changes are seen in VaD; mostly in white matter, whereas in AD they predominate in cortical grey matter. The regional distribution of grey matter involvement may differ between AD and other degenerative dementias. Hence, both the nature and anatomic distribution of metabolite abnormalities contribute to diagnostic discrimination with MRS. NAA/mI ratios from short echo time spectra of the posterior cingulate region cortex discriminate reliably between AD subjects, normal individuals and those with VaD, and provides a useful clinical test, as an adjunct to structural imaging. Elevated mI is detected in mild cognitive impairment (MCI) and quantitative metabolite measures correlate with degrees of cognitive impairment in AD; these suggest a possible role for MRS in early diagnosis and for surrogate biochemical markers for monitoring disease progression and therapeutic response.
Gold discoveries in 1848 set off a large and extremely rapid migration to California. This article uses newly collected data from the 1850 and 1852 Censuses of Population together with the public use sample of the 1850 Census of Population to examine who went to California and how they did economically. We find that the propensity to migrate was affected by the individual's age and literacy, distance of the state from California, and average state latitude. Consistent with the historical literature, we find that economic outcomes were generally small or even zero for miners but were positive and large for nonminers.
This document, as well as any data and map included herein, are without prejudice to the status of or sovereignty over any territory, to the delimitation of international frontiers and boundaries and to the name of any territory, city or area. 2 │ ECO/WKP(2018)58 ENHANCING DYNAMISM IN SMES AND ENTREPRENEURSHIP IN KOREA Unclassified OECD Working Papers should not be reported as representing the official views of the OECD or of its member countries. The opinions expressed and arguments employed are those of the author(s). Working Papers describe preliminary results or research in progress by the author(s) and are published to stimulate discussion on a broad range of issues on which the OECD works.
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