Anodal Transcranial Direct Current Stimulation Over Prefrontal Cortex Slows Sequence Learning in Older Adults

Aging is associated with declines in sensorimotor function. Several studies have demonstrated that transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, can be combined with training to mitigate age-related cognitive and motor declines. However, in some cases, the application of tDCS disrupts performance and learning. Here, we applied anodal tDCS either over the left prefrontal cortex (PFC), right PFC, supplementary motor complex (SMC), the left M1, or in a sham condition while older adults (n = 63) practiced a Discrete Sequence Production (DSP), an explicit motor sequence, task across 3 days. We hypothesized that stimulation to either the right or left PFC would enhance motor learning for older adults, based on the extensive literature showing increased prefrontal cortical activity during motor task performance in older adults. Contrary to our predictions, stimulation to the right and left PFC resulted in slowed motor learning, as evidenced by a slower reduction rate of reduction of reaction time and the number of sequence chunks across trials relative to sham in session one and session two, respectively. These findings suggest an integral role of the right PFC early in sequence learning and a role of the left PFC in chunking in older adults, and contribute to mounting evidence of the difficultly of using tDCS in an aging population

The effect of natural fracture heterogeneity on hydraulic fracture performance and seismic response in shale and coal formations

Two 0.3 m × 0.3 m × 0.3 m cubic blocks of shale and coal were used for hydraulic fracturing experiments under true tri-axial stress conditions. The shale block used was highly homogeneous and without visible fractures, while the coal block contained a host of natural fractures. The mechanical and hydraulic properties of both rocks were characterized through multi-stage triaxial tests, Brazilian disk tests, and porosity and permeability measurements. A true tri-axial rock testing machine equipped with loading, pump and acoustic systems was used in the experiment. The acoustic system uses 48 transducers with active sources to repetitively generate and receive ultrasonic P/S wave pulses to reveal fracture initiation and growth. Before the experiment, initial seismic response of both blocks was recorded under hydrostatic stress conditions to characterize anisotropy and heterogeneity of the blocks as reference. Silicon oil was injected centrally into both blocks to create a hydrofracture under deviatoric stress conditions and the load, displacement, pump pressure and volume, and seismic response during the injection process were recorded. Results from two blocks are being compared in terms of hydrofracture geometry and seismic features

Histopathological changes in the reproductive system (ovaries and testes) of Oreochromis mossambicus following exposure to DDT

A b s t r a c t This study assesses the effects of 1,1-bis (4-chlorophenyl)-2,2,2-trichloroethane (DDT) on the reproduction and gonadal histology of adult Mozambique tipalia (Oreochromis mossambicus). The fish were allowed to breed, following exposure to 2 and 5 jig/l of waterborne technical-grade DDT for 40 days. Fertilized eggs were artificially incubated. In the 5 jig/l exposure, posthatch survival was significantly lower, and prevalence of larval skeletal deformities significantly higher, compared to the control (p<0.05). Incomplete axial development was the common gross deformity in posthatch larvae, caused by failure to develop chondroblasts posterior to the buccopharyngeal cavity. There were no significant differences in the gonadosomatic index of exposed and non-exposed male and female adults. The exposure caused increased oocyte atresia in the ovaries and disorganization of seminiferous lobules in the testes of adults. DDT exposure reduced survival and increased deformities in larvae, at levels that did not cause severe histopathological changes to parental gonads

The use of the urogenital papillae of male feral African sharptooth catfish (Clarias gariepinus) as indicator of exposure to estrogenic chemicals in two polluted dams in an urban nature reserve, Gauteng, South Africa

The African sharptooth catfish (Clarias gariepinus) is indigenous to South Africa where it is commonly found in calm waters such as lakes, streams, rivers, swamps and floodplains. The males of this gonochoristic species can be readily distinguished from females via a distinct elongated urogenital papilla with a pointed tip, located just behind the anus. This structure is an androgen controlled secondary sexual characteristic and could potentially be affected by chemicals displaying endocrine disrupting properties during development. Results of previous studies on effects on papillae of different fish species indicated that these structures could be useful as bio-indicators of exposure due to alterations in the structures. This study investigated the occurrence of abnormal morphology in urogenital papillae compared to the macroscopic and microscopic structure of the gonads of presumed male or intersex catfish sampled from the Rietvlei and Marais dams in an urban nature reserve, due to exposure to endocrine disrupting chemicals (EDCs). Macroscopic observation of the UGP, gonad examination after laparotomy and histology were done. Gonadosomatic index (GSI) and Urogenital papilla length index (UGPLI) were determined for all fish collected. Mesenteric fat analyzed for selected alkylphenols and organochlorines showed high levels of especially nonylphenol indicating long term exposure to these chemicals due to bio-accumulation. The GSI indicated that fish with intersex gonads were probably feminized males. It was concluded that use of the UGP alone, without macroscopic and microscopic analyses of the gonads, could not effectively indicate exposure to EDCs.Water Research Commission (WRC) of South Africahttp://www.elsevier.com/locate/ecoenvhb201

QRTEngine: An easy solution for running online reaction time experiments using Qualtrics

Performing online behavioral research is gaining increased popularity among researchers in psychological and cognitive science. However, the currently available methods for conducting online reaction time experiments are often complicated and typically require advanced technical skills. In this article, we introduce the Qualtrics Reaction Time Engine (QRTEngine), an open-source JavaScript engine that can be embedded in the online survey development environment Qualtrics. The QRTEngine can be used to easily develop browser-based online reaction time experiments with accurate timing within current browser capabilities, and it requires only minimal programming skills. After introducing the QRTEngine, we briefly discuss how to create and distribute a Stroop task. Next, we describe a study in which we investigated the timing accuracy of the engine under different processor loads using external chronometry. Finally, we show that the QRTEngine can be used to reproduce classic behavioral effects in three reaction time paradigms: a Stroop task, an attentional blink task, and a masked-priming task. These findings demonstrate that QRTEngine can be used as a tool for conducting online behavioral research even when this requires accurate stimulus presentation times

Auditory presentation and synchronization in Adobe Flash and HTML5/JavaScript Web experiments

Substantial recent research has examined the accuracy of presentation durations and response time measurements for visually presented stimuli in Web-based experiments, with a general conclusion that accuracy is acceptable for most kinds of experiments. However, many areas of behavioral research use auditory stimuli instead of, or in addition to, visual stimuli. Much less is known about auditory accuracy using standard Web-based testing procedures. We used a millisecond-accurate Black Box Toolkit to measure the actual durations of auditory stimuli and the synchronization of auditory and visual presentation onsets. We examined the distribution of timings for 100 presentations of auditory and visual stimuli across two computers with difference specs, three commonly used browsers, and code written in either Adobe Flash or JavaScript. We also examined different coding options for attempting to synchronize the auditory and visual onsets. Overall, we found that auditory durations were very consistent, but that the lags between visual and auditory onsets varied substantially across browsers and computer systems