Effect of task difficulty on blood-oxygen-level-dependent signal: A functional magnetic resonance imaging study in a motion discrimination task

<div><p>There is much evidence that neural activity in the human brain is modulated by task difficulty, particularly in visual, frontal, and parietal cortices. However, some basic psychophysical tasks in visual perception do not give rise to this expected effect, at least not in the visual cortex. In the current study, we used functional magnetic resonance imaging (fMRI) to record brain activity while systematically manipulating task difficulty in a motion discrimination task, by varying the angular difference between the motion direction of random dots and a reference direction. We used both a blocked and an event-related design, and presented stimuli in both central and peripheral vision. The behavioral psychometric function, across angular differences of 3°, 9°, 15°, or 80°, spanned the full response range, as expected. The mean blood oxygen level dependent (BOLD) signals were also correlated within-participants between the blocked and event-related designs, across all brain areas tested. Within the visual cortex, the voxel response patterns correlated more within-conditions (e.g., 3° and 3°) than between-conditions (e.g., 3° and 9°), in both designs, further attesting to the reasonable quality of the BOLD data. Nevertheless, the BOLD-o-metric functions (i.e., BOLD activity as a function of task difficulty) were flat in the whole-brain and region-of-interest (ROI) analyses, including in the visual cortex, the parietal cortex, in both designs, and in foveal and peripheral visual fields alike. Indeed, there was little difference between BOLD activity during the 3° and 80° conditions. Some suggestive evidence of difficulty modulation was revealed only in the superior and inferior frontal gyri for the blocked design. We conclude that, in motion discrimination, there is no systematic BOLD modulation that accompanies the standard psychometric function across different hierarchies of cortical areas, except for the frontal lobe of the brain.</p></div

Behavioral results: Experiments 1 and 2.

<p>Behavioral accuracies averaged across 14 participants in 3°, 9°, and 15° conditions for the blocked (A) and event-related (B) designs in Experiment 1; and across 10 participants in 3°, 9°, 15°, and 80° conditions for the blocked (C) and event-related (D) designs in Experiment 2. Error bars denote 1 SEM of the mean here and in all subsequent figures.</p

MVPA results.

<p>The correlation between activity patterns of motion stimuli within the same condition was larger than that between different conditions in Experiment 1 (A) and in Experiment 2 (B).</p

MRI results of ROI analysis: Experiment 2.

<p>BOLD amplitudes averaged across 10 participants for the 3°, 9°, 15°, and 80° conditions in V1, V2, V3, V3a, V4, MT+, and IPS for the blocked design (A) and the event-related design (B).</p

The 42 Talairach coordinates for ROI analysis in the higher-order cortex.

<p>The 42 Talairach coordinates for ROI analysis in the higher-order cortex.</p

In vivo antitumor activity of DOX-hyd-PEG-FA NPs.

<p>Athymic nude mice xenografted with KB cells were intravenously injected with different doses of DOX-hyd-PEG-FA NPs (2.5, 5 and 10 mg/kg equivalent DOX) and one dose of DOX (5 mg/kg) every 7 day (days 1, 7, and 14). Panel <b>A</b>-tumor volume changes of tumor bearing mice, *P<0.05 vs free DOX, ^#P<0.05 vs 5 mg/kg DOX-hyd-PEG-FA NPs, n = 3. Panel <b>B</b>-body weight changes in tumor bearing nude mice, *P<0.05 vs free DOX, n = 3. Panel <b>C</b>-survival curve of tumor bearing mice. *P<0.05 vs free DOX, n = 3.</p

Genome Re-Sequencing and Functional Analysis Places the <i>Phytophthora sojae</i> Avirulence Genes <i>Avr1c</i> and <i>Avr1a</i> in a Tandem Repeat at a Single Locus

<div><p>The aim of this work was to map and identify the <i>Phytophthora sojae Avr1c</i> gene. Progeny from a cross of <i>P. sojae</i> strains ACR10×P7076 were tested for virulence on plants carrying <i>Rps</i>1c. Results indicate that avirulence segregates as a dominant trait. We mapped the <i>Avr1c</i> locus by performing whole genome re-sequencing of composite libraries created from pooled samples. Sequence reads from avirulent (Pool1) and virulent (Pool2) samples were aligned to the reference genome and single nucleotide polymorphisms (SNP) were identified for each pool. High quality SNPs were filtered to select for positions where SNP frequency was close to expected values for each pool. Only three SNP positions fit all requirements, and these occurred in close proximity. Additional DNA markers were developed and scored in the F₂ progeny, producing a fine genetic map that places <i>Avr1c</i> within the <i>Avr1a</i> gene cluster. Transient expression of <i>Avr1c</i> or <i>Avr1a</i> triggers cell death on <i>Rps</i>1c plants, but <i>Avr1c</i> does not trigger cell death on <i>Rps</i>1a plants. Sequence comparisons show that the RXLR effector genes <i>Avr1c</i> and <i>Avr1a</i> are closely related paralogs. Gain of virulence on <i>Rps</i>1c in <i>P. sojae</i> strain P7076 is achieved by gene deletion, but in most other strains this is accomplished by gene silencing. This work provides practical tools for crop breeding and diagnostics, as the <i>Rps</i>1c gene is widely deployed in commercial soybean cultivars.</p></div

Genomic DNA blot hybridization showing <i>P. sojae</i> strain-specific deletions of <i>Avr1a</i> and <i>Avr1c</i>.

<p>Selected strains of <i>P. sojae</i> genomic DNA were digested with <i>Pml</i>I and separated by electrophoresis prior to blotting and hybridization. Virulence phenotype of the <i>P. sojae</i> strains on <i>Rps</i>1c or <i>Rps</i>1a plants is shown as virulent (V) or avirulent (A). The positions and sizes of the <i>Pml</i>I segments of <i>Avr1a</i>, <i>Avr1c</i>, and <i>Avh72</i> genes are indicated on the right. The sizes of DNA markers are shown on the left; kb, kilo base pair. The <i>Avr1c</i> gene is deleted from parental strain P7076.</p

Statistic analysis of survival of tumor bearing mice.

<p>a-compared with control, b-compared with free DOX.</p

Cytotoxicity for A549 cells, KB cells and HepG2 cells treated with DOX, DOX-hyd-PEG-FA NPs, DOX-hyd-PEG NPs, DOX-ami-PEG-FA NPsz and DOX-ami-PEG NPs.

<p>*p<0.05,</p><p>**p<0.01 vs DOX-ami-PEG-FA NPs.</p>#<p>p<0.05,</p>##<p>p<0.01 vs DOX-hyd-PEG NPs.</p>$<p>p<0.05,</p>$$<p>p<0.01 vs DOX.</p