The Emergence of Miller's Magic Number on a Sparse Distributed Memory

Human memory is limited in the number of items held in one's mind—a limit known as “Miller's magic number”. We study the emergence of such limits as a result of the statistics of large bitvectors used to represent items in memory, given two postulates: i) the Sparse Distributed Memory; and ii) chunking through averaging. Potential implications for theoretical neuroscience are discussed

Threshold values.

<p>Thresholds given plausible success factors and dimension combinations.</p

Preserved items as a function of ; selected values of .

<p>Preserved items as a function of ; selected values of .</p

Cardiac autonomic activity predicts dominance in verbal over spatial reasoning tasks : results from a preliminary study

Abstract: The present study sought to determine whether autonomic activity is associated with dominance in verbal over spatial reasoning tasks. A group of 19 healthy adults who performed a verbal and spatial aptitude test was evaluated. Autonomic function was assessed by means of heart rate variability analysis, before and during the tasks. The results showed that a better relative performance in verbal over spatial reasoning tasks was associated with vagal prevalence in normal subjects

Heart rate nonlinear dynamics during sudden hypoxia at 8,230 m simulated altitude

Background: Acute hypobaric hypoxia is associated with autonomic changes that bring a global reduction of linear heart rate variability (HRV). Although changes in nonlinear HRV can be associated with physiological stress and are relevant predictors of fatal arrhythmias in ischemic heart disease, to what extent these components vary in sudden hypobaric hypoxia is not known. Methods: Twelve military pilots were supplemented with increasing concentrations of oxygen during decompression to 8,230 m in a hypobaric chamber. Linear and nonlinear HRV was evaluated at 8,230 m altitude before, during and after oxygen flow deprivation. Linear HRV was assessed through traditional time- and frequency- domain analysis. Nonlinear HRV was quantified through the short term fractal correlation exponent alpha (αs) and the Sample Entropy index (SampEn). Results: Hypoxia was related to a decrease in linear heart rate variability indexes at all frequency levels. A non significant decrease in αs (basal: 1.39 ± 0.07, hypoxia: 1.11 ± 0.13, recovery: 1.41 ± 0.05, p = 0.054) and a significant increase in SampEn (basal: 1.07 ± 0.11, hypoxia: 1.45 ± 0.12, recovery: 1.43 ± 0.09, p = 0.018) were detected. Conclusions: The observed pattern of diminished linear heart rate variability and increased nonlinear heart rate variability is similar to that seen in subjects undergoing heavy exercise or in patients with ischemic heart disease and high risk for ventricular fibrillation

Glioma Groups Based on 1p/19q, IDH, and TERT Promoter Mutations in Tumors.

BackgroundThe prediction of clinical behavior, response to therapy, and outcome of infiltrative glioma is challenging. On the basis of previous studies of tumor biology, we defined five glioma molecular groups with the use of three alterations: mutations in the TERT promoter, mutations in IDH, and codeletion of chromosome arms 1p and 19q (1p/19q codeletion). We tested the hypothesis that within groups based on these features, tumors would have similar clinical variables, acquired somatic alterations, and germline variants.MethodsWe scored tumors as negative or positive for each of these markers in 1087 gliomas and compared acquired alterations and patient characteristics among the five primary molecular groups. Using 11,590 controls, we assessed associations between these groups and known glioma germline variants.ResultsAmong 615 grade II or III gliomas, 29% had all three alterations (i.e., were triple-positive), 5% had TERT and IDH mutations, 45% had only IDH mutations, 7% were triple-negative, and 10% had only TERT mutations; 5% had other combinations. Among 472 grade IV gliomas, less than 1% were triple-positive, 2% had TERT and IDH mutations, 7% had only IDH mutations, 17% were triple-negative, and 74% had only TERT mutations. The mean age at diagnosis was lowest (37 years) among patients who had gliomas with only IDH mutations and was highest (59 years) among patients who had gliomas with only TERT mutations. The molecular groups were independently associated with overall survival among patients with grade II or III gliomas but not among patients with grade IV gliomas. The molecular groups were associated with specific germline variants.ConclusionsGliomas were classified into five principal groups on the basis of three tumor markers. The groups had different ages at onset, overall survival, and associations with germline variants, which implies that they are characterized by distinct mechanisms of pathogenesis. (Funded by the National Institutes of Health and others.)