Heritability of Stroop and flanker performance in 12-year old children

Background  

There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks.     

The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

Background  

In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment.     

Precise mass measurement of a double-stranded 500 base-pair (309 kDa) polymerase chain reaction product by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd.     

Separation of different physical forms of plasmid DNA using a combination of low electric field strength and flow in porous media: effect of different field gradients and porosity of the media

The retention of different physical forms of DNA by an electric field in a chromatography system was studied. We were able to effectively separate the supercoiled and the open circular forms of plasmid DNA using this type of electrochromatography system. Chromatography columns were packed with porous beads, and an axial electric field was applied so that convective buffer flow opposed the direction of electrophoresis of the DNA. A model system composed of approximately equal amounts of the super-coiled and open circular forms of the plasmid pBR 322 (4322 base pairs) was used to test the separation. Chromatography beads (agarose-based) with different porosities were used to determine the effect of the stationary phase on the separation. The porous media did not have a major effect on the separation, but the best separations were obtained using porous chromatography media made with the highest agarose concentration (10% agarose). Selective elution of plasmid DNA with different forms was obtained by either increasing the flow rates or decreasing the electric field strength (by steps or a gradient). In all the separations, the more compact supercoiled form of the plasmid was retained less strongly than either the open circular form (nicked) or the linear form. High molecular weight host genomic DNA was more strongly retained than the plasmid DNA. Increasing the ionic strength of the buffer improved resolution and capacity. The capacity of the separation was determined by injecting increasing amounts of plasmid DNA. Satisfactory separation was obtained at sample loading of up to 360 microg of total DNA on a column with dimensions of 2.5 by 11 cm (bed volume of 54 mL). The retention of DNA depends upon a counter-current flow of electrophoresis and convective flow and could be regarded as a type of field flow fractionation. The retention of the DNA by the electric field and flow is discussed in relation to the diffusion coefficients of the DNA.