Sequence Of Triplets Research Articles

Auditory multistability and neurotransmitter concentrations in the human brain.

Multistability in perception is a powerful tool for investigating sensory-perceptual transformations, because it produces dissociations between sensory inputs and subjective experience. Spontaneous switching between different perceptual objects occurs during prolonged listening to a sound sequence of tone triplets or repeated words (termed auditory streaming and verbal transformations, respectively). We used these examples of auditory multistability to examine to what extent neurochemical and cognitive factors influence the observed idiosyncratic patterns of switching between perceptual objects. The concentrations of glutamate-glutamine (Glx) and γ-aminobutyric acid (GABA) in brain regions were measured by magnetic resonance spectroscopy, while personality traits and executive functions were assessed using questionnaires and response inhibition tasks. Idiosyncratic patterns of perceptual switching in the two multistable stimulus configurations were identified using a multidimensional scaling (MDS) analysis. Intriguingly, although switching patterns within each individual differed between auditory streaming and verbal transformations, similar MDS dimensions were extracted separately from the two datasets. Individual switching patterns were significantly correlated with Glx and GABA concentrations in auditory cortex and inferior frontal cortex but not with the personality traits and executive functions. Our results suggest that auditory perceptual organization depends on the balance between neural excitation and inhibition in different brain regions.This article is part of the themed issue 'Auditory and visual scene analysis'.

Sequential Auditory Scene Analysis Is Preserved in Normal Aging Adults

Normal aging is accompanied by speech perception difficulties, especially in adverse listening situations such as a cocktail party. To assess whether such difficulties might be related to impairments in sequential auditory scene analysis, event-related brain potentials were recorded from normal-hearing young, middle-aged, and older adults during presentation of low (A) tones, high (B) tones, and silences (--) in repeating 3 tone triplets (ABA--). The likelihood of reporting hearing 2 streams increased as a function of the frequency difference between A and B tones (Delta f) to the same extent for all 3 age groups and was paralleled by enhanced sensory-evoked responses over the frontocentral scalp regions. In all 3 age groups, there was also a progressive buildup in brain activity from the beginning to the end of the sequence of triplets, which was characterized by an enhanced positivity that peaked at about 200 ms after the onset of each ABA--triplet. Similar Delta f- and buildup-related activity also occurred over the right temporal cortex, but only for young adults. We conclude that age-related difficulties in separating competing speakers are unlikely to arise from deficits in streaming and might instead reflect less efficient concurrent sound segregation.

Genetics of Childhood Disorders: VIII. Making Sense Out of Nonsense

DNA is a biological polymer that encodes information essential for all physiological processes. The cell devotes considerable resources to maintain the integrity of this information. High priority is given to repairing DNA damage in an ongoing manner, and stringent proofreading mechanisms are in place in dividing cells. Despite these safeguards, however, alterations do occur to the original sequence. These changes may have no effect or can actually benefit the organism as occurs during evolutionary changes. When the alterations are deleterious we recognize these changes as mutations. Mutations may cause inherited disease when they are present in parental gametes and are passed on to the next generation. They may cause acquired disease when they develop de novo in somatic cells. An example of the former would include achondroplasia, a disorder in which affected individuals have short-limbed dwarfism. This illness results from a mutation in the fibroblast growth factor receptor-3 gene (FGFR?). Examples of acquired disorders are characteristically found in neoplasms, such as those affecting the p53 tumor suppressor gene. A key distinction between these 2 forms of mutations is that inherited mutations are present in all cells of the offspring, whereas acquired mutations affect only a subgroup of cells in an individual. Ten percent of the DNA in the human genome codes for genes. This indicates that a random mutation is more likely to affect intergenic DNA than DNA coding for proteins. While the principal disease-causing effect of mutations seems to be on coding sequences within genes, it is now appreciated that some mutations of the DNA lying between genes have functional consequences on gene expression. This realization is based on the recognition that the intergenic DNA contains sequences essential for the normal regulation of nearby genes. This regulation is usually referred to as epigenetic (pi: upon, higher than), so mutations are also classified as genetic (affecting coding sequences) or epigenetic (affecting gene regulation). Most genes may be divided into functional regions. The promoter area is where the transcriptional machinery gains access to the DNA strand to initiate transcription. Nearby regulatory sequences determine the correct timing of transcription, the level of gene expression, and the specific cell type in which transcription will occur. In addition to these regulatory regions, a gene also contains the exons which actually encode for protein and which must be spliced together to form the processed or mature messenger RNA (mRNA) molecule. The mRNA is then read by the translational machinery as a sequence of triplets. Each triplet of nucleotides encodes individual amino acids that are strung together to form a protein molecule. The sequence of triplets is termed the coding sequence or open reading frame of the mRNA. Much of this material may be reviewed in 2 earlier columns on transcriptional control (April

The genetic revolution 1950–1996: an introduction

During the last 40 years or so there has been an exponential growth in our knowledge of biology and medicine and, within this period, several discoveries stick out as particularly important. The opening salvo for all later revolutionary developments was the clarification of the structure of DNA by Watson and Crick in the early 1950s. Another milestone was the breaking of the genetic code by Holley, Khorana and Nierenberg in the 1960s. Nowadays, most people know that DNA is made up from a double helix of deoxyribonucleic acid, where the genetic information is laid down in the sequence of the DNA building blocks, the nucleotides. Genes, as we now know, are in principle nothing other than sections of the chromosomal DNA harbouring, in the sequence of contiguous nucleotide triplets, the genetic information for the synthesis of proteins, as a rule one protein per gene.

Symbolic representation of hyperspectral data

We have developed a symbolic representation of hyperspectral data using the scale space techniques of Witkin. We created a scale space image of hyperspectral data from convolution with Gaussian masks and then a fingerprint that extracts individual features from the original data. The fingerprint provides a context that pairs inflection points and assigns them to a feature, generates a measure of importance for each feature, and relates features to each other. The representation is an ordered sequence of triplets containing a measure of importance related to the area of each feature and the left and right inflection points of the feature. The description is compact, quantitative, and hierarchical, describing the hyperspectral curve by its most important structural features first, followed by features of lesser importance.

Studies on the bacteriophage MS2: I. Distribution of purine sequences in the viral RNA and in yeast RNA

Methods have been worked out for digestion of RNA with pancreatic ribonuclease and for fractionation of the products. In appropriate conditions the hydrolysis seemed to proceed strictly according to the known specificity of the enzyme. The resulting oligonucleotides of general formula (purine nucleotide) n pyrimidine nucleotide were separated on the basis of chain length by chromatography on DEAE-cellulose in the presence of 7 M -urea. Other factors, however, influenced the separation as well. The methodology was worked out by means of yeast RNA and some of these results are presented. The distribution of purines in the bacteriophage MS2 RNA reveals a striking pattern of alternating excess ( n = 0, 2, 4, 6, 8) and deficit ( n = 1, 3, 5, 7) over the amount calculated on the basis of a random distribution. A similar rhythm is present in yeast RNA. The estimated number of the various tracts per MS2 RNA molecule are reported. There occur three octanucleotides, three nonanucleotides and two decanucleotides ( n respectively 7, 8 and 9). The minimum molecular weight, based on the decanucleotide content, amounts to 1·06 × 10 6 , which is in complete agreement with the physical value. The implications of the results, especially the rhythmic distribution, for the genetic code are discussed. It may be concluded that the sequence of triplets is not random, but subject to a higher degree of order.

Progress in Medical Genetics.

The ides of March have brought with them the new volume of Steinberg and Bearn's<i>Progress in Medical Genetics</i>, by now a fairly reliable sign of spring and, hopefully, a portent of a possible annual appearance of this splendid review and essay series. The over-all quality of the contributions to this volume is altogether superb, and Drs. Steinberg and Bearn are to be congratulated for being able to obtain again the cooperation of such outstanding collaborators. Bernard Strauss has the first word with a magnificent chapter on chemical mutagens and the genetic code. The first one half of this essay is devoted to a review of the evidence for the hypothesis that genetic information is encoded in the base sequence of DNA; that this code probably consists of a nonoverlapping linear sequence of nucleotide-pair triplets and that it is highly degenerate; furthermore, that the base sequence of a section of