Biology subjects

Koizumi, K.

Publications and source records attributed to Koizumi, K..

4 recordsLinked to original sources

bioRxiv2026

tACS increases alpha burst duration in a frequency- and montage-specific manner

Transcranial alternating current stimulation (tACS) can experimentally manipulate neural oscillations in humans non-invasively. Previous studies consistently suggest that 10 Hz tACS in posterior regions leads to a general increase in alpha (7-15 Hz) oscillations. However, the specificity of this effect regarding stimulation frequency and location as well as its consequences on cognition are still unclear. We therefore aimed to investigate whether the putative effects of tACS on neural oscillations and cognition are specific to posterior stimulation in the alpha frequency range. We tested these effects using a 2 x 2 design (posterior or fronto-parietal stimulation, at 10 Hz or 6 Hz) plus a no-stimulation control group, during a sustained attention task.158 healthy participants were randomly allocated to control group (no stimulation) or one of the four active groups. All participants underwent an Electroencephalography recording and completed the Amsterdam Resting State Questionnaire before and after stimulation. Our results show that, relative to the control group, alpha power increases significantly after stimulation for the group receiving posterior 10 Hz stimulation and that this was explained by an increase in alpha oscillatory bursts duration rather than their amplitude. On the other hand, no significant differences were found between active and controls groups in behavioural performance or resting state cognition. Together, our findings demonstrate that tACS increases the duration of alpha oscillatory bursts in a montage- and frequency-specific manner and that this modulation is not accompanied by significant changes in sustained attention during stimulation or resting state cognition after stimulation.

neuroscience↗

bioRxiv2022

Spatial control of ARGONAUTE-mediated RNA silencing in anther development

Argonaute protein (AGO) in association with small RNAs is the core machinery of RNA silencing, an essential mechanism for precise development and defense against pathogens in many organisms. Here, we identified two AGOs in rice anthers, AGO1b and AGO1d, that interact with phased small interfering RNAs (phasiRNAs) derived from numerous long non-coding RNAs. Moreover, 3D-immunoimaging and mutant analysis demonstrated that rice AGO1b and AGO1d redundantly and cell type-specifically regulate anther development by acting as mobile carriers of these phasiRNAs from the somatic cell layers to the germ cells in anthers. Our study also highlights a new mode of reproductive RNA silencing via the specific nuclear and cytoplasmic localization of three AGOs, AGO1b, AGO1d, and MEL1, in rice pollen mother cells.

plant biology↗

bioRxiv2020

Color morphs of the coral, Acropora tenuis, show different responses to environmental stress and different expression profiles of fluorescent-protein genes

Corals of the family Acroporidae are key structural components of reefs that support the most diverse marine ecosystems. Due to increasing anthropogenic stresses, coral reefs are in decline. Along the coast of Okinawa, Japan, three different color morphs of Acropora tenuis have been recognized for decades. These include brown (N morph), yellow-green (G) and purple (P) forms. The tips of axial coral polyps exhibit specific fluorescence spectra. This attribute is inherited asexually, and color morphs do not change seasonally. In Okinawa Prefecture, during the summer of 2017, the N and P morphs experienced bleaching, in which some N morphs died while P morphs recovered. In contrast, G morphs successfully withstood the stress. Symbiotic dinoflagellates are essential symbiotic partners of scleractinian corals. Photosynthetic activity of symbionts was reduced in July in N and P morphs; however, the three color-morphs host similar sets of Clade-C zoothanthellae, suggesting that beaching of N and P morphs cannot be attributed to differences in symbiont clades. The decoded Acropora tenuis genome includes five genes for green fluorescent proteins (GFP), two for cyan fluorescent proteins (CFP), three for red fluorescent proteins (RFP), and seven genes for chromoprotein (ChrP). A summer survey of gene expression profiles demonstrated that (a) expression of CFP and REP was quite low in all three morphs, (b) P morphs expressed higher levels of ChrP, (c) both N and G morphs expressed GFP highly, and (d) GFP expression was reduced in N morphs, compared to G morphs, which maintained higher levels of GFP expression throughout the summer. Although further studies are required to understand the biological significance of these color morphs of Acropora tenuis, our results suggest that thermal stress resistance is modified by genetic mechanisms that coincidentally lead to diversification of color morphs.

evolutionary biology↗

bioRxiv2020

The effects of transcranial direct current stimulation on the brain networks related to creative thinking

Human creative thinking is unique and capable of generating novel and valuable ideas. Recent research has clarified the contribution of different brain networks (default mode network, DN; executive control network; salience network) to creative thinking. However, the effects of brain stimulation on brain networks during creative thinking and on creative performance have not been clarified. The present study was designed to examine the changes in functional connectivity (FC) and effective connectivity (EC) of the large-scale brain network, and the ensuing changes in creative performance, induced by transcranial direct current stimulation (tDCS). Fourteen healthy male students underwent two tDCS sessions, one with actual stimulation and one with sham stimulation, on two separate days. Participants underwent tDCS (anode over the left dorsolateral prefrontal cortex, DLPFC; cathode over the right inferior parietal lobule, IPL) for 20 minutes. Before and after the tDCS session, electroencephalography signals were acquired from 32 electrodes over the whole head during the creative thinking task. On FC analysis, the delta band FC between the posterior cingulate cortex and IPL significantly increased only after real stimulation. We also found that the change of flexibility score was significantly correlated with the change in (i) delta band FC between mPFC and left lateral temporal cortex (LTC) and (ii) alpha band FC between IPL and right LTC. On EC analysis, decreased flow within the DN (from left LTC to right IPL) was observed. Our results reveal that tDCS could affect brain networks, particularly the DN, during creative thinking and modulate key FC in the generation of flexible creative ideas.

neuroscience↗