Overlapping influences shape motor activity during hasty sensorimotor decisions

Humans and other animals are able to adjust their speed-accuracy tradeoff (SAT) at will depending on the urge to act, favoring either cautious or hasty decision policies in different contexts. An emerging view is that SAT regulation relies on influences exerting broad changes on the motor system, tuning its activity up globally when hastiness is at premium. The present study aimed to test this hypothesis. Fifty subjects performed a task involving choices between left and right index fingers, in which incorrect choices led either to a high or to a low penalty in two contexts, inciting them to emphasize either cautious or hasty policies. We applied transcranial magnetic stimulation on multiple motor representations, eliciting motor evoked potentials (MEP) in nine finger and leg muscles. MEP amplitudes allowed us to probe activity changes in the corresponding finger and leg representations, while subjects were deliberating about which index to choose. Our data indicate that hastiness entails a broad amplification of motor activity, though this amplification was limited to the chosen side. On top of this effect, we identified a local suppression of motor activity, surrounding the chosen index representation. Hence, a decision policy favoring speed over accuracy appears to rely on overlapping processes producing a broad (but not global) amplification and a surround suppression of motor activity. The latter effect may help increasing the signal-to-noise ratio of the chosen representation, as supported by single-trial correlation analyses indicating a stronger differentiation of activity changes in finger representations in the hasty context.

Growth Rate-Dependent Global Amplification of Gene Expression

Regulation of cell growth rate is essential for maintaining cellular homeostasis and survival in diverse conditions. Changes in cell growth rate result in changes in rRNA and tRNA content, but the effect of cell growth rate on mRNA abundance is not known. We developed a new method for measuring absolute transcript abundances using RNA-seq, SPike in-based Absolute RNA Quantification (SPARQ), that does not assume a constant transcriptome size and applied it to the model eukaryote, Saccharomyces cerevisiae (budding yeast), grown at different rates. We find that increases in cell growth rate result in increased absolute abundance of almost every transcript, with significant coordinated changes in abundances among functionally related transcripts. mRNA degradation and synthesis rates increase with increased growth rate, but to differing extents, resulting in the observed net increases in absolute abundance. We propose that regulation of ribosome abundance links environmental conditions to transcriptome amplification via nutrient-sensing pathways.

A molecular analysis of the population of mRNA in bovine spermatozoa

Spermiogenesis represents the transition from haploid spermatids to spermatozoa. This process entails an extreme condensation of the nucleus and a loss of nearly all cytoplasmic content. The presence of messenger RNAs in the spermatozoa has previously been shown. Generally, these transcripts are considered to be remnants of spermiogenesis. However, it has recently been proposed that there may exist a function for these sperm-associated RNAs. To address the possibility of a functional role for these transcripts, we sought to investigate and characterize the RNA pool found in bovine spermatozoa. The main goals of this study were to examine RNA integrity and survey the mRNA found in spermatids and spermatozoa. Assessment of mRNAs integrity was performed by three approaches: microelectrophoresis, comparative smearing after global amplification, and PCR amplification of target sequences located either in the 5′ or the 3′ ends, while mRNAs survey was performed by microarray hybridizations. RNA integrity studies in the spermatozoa showed a majority of low molecular size fragments indicating a natural segmentation of the mRNA population. The mRNA survey indicated that the sperm transcriptome harbors a complex mixture of messengers implicated in a wide array of cell functions and representing a large subset of transcripts found in spermatids. Subsequently, such sperm RNA profiling could allow the molecular diagnosis of male gamete quality.