Bayesian-based decipherment of in-depth information in bacterial chemical sensing beyond pleasant/unpleasant responses.

Chemical sensing is vital to the survival of all organisms. Bacterial chemotaxis is conducted by multiple receptors that sense chemicals to regulate a single signalling system controlling the transition between the direction (clockwise vs. counterclockwise) of flagellar rotation. Such an integrated system seems better suited to judge chemicals as either favourable or unfavourable, but not for identification purposes though differences in their affinities to the receptors may cause difference in response strength. Here, an experimental setup was developed to monitor behaviours of multiple cells stimulated simultaneously as well as a statistical framework based on Bayesian inferences. Although responses of individual cells varied substantially, ensemble averaging of the time courses seemed characteristic to attractant species, indicating we can extract information of input chemical species from responses of the bacterium. Furthermore, two similar, but distinct, beverages elicited attractant responses of cells with profiles distinguishable with the Bayesian procedure. These results provide a basis for novel bio-inspired sensors that could be used with other cell types to sense wider ranges of chemicals.

Macroscopic neural mass model constructed from a current-based network model of spiking neurons.

Neural mass models (NMMs) are efficient frameworks for describing macroscopic cortical dynamics including electroencephalogram and magnetoencephalogram signals. Originally, these models were formulated on an empirical basis of synaptic dynamics with relatively long time constants. By clarifying the relations between NMMs and the dynamics of microscopic structures such as neurons and synapses, we can better understand cortical and neural mechanisms from a multi-scale perspective. In a previous study, the NMMs were analytically derived by averaging the equations of synaptic dynamics over the neurons in the population and further averaging the equations of the membrane-potential dynamics. However, the averaging of synaptic current assumes that the neuron membrane potentials are nearly time invariant and that they remain at sub-threshold levels to retain the conductance-based model. This approximation limits the NMM to the non-firing state. In the present study, we newly propose a derivation of a NMM by alternatively approximating the synaptic current which is assumed to be independent of the membrane potential, thus adopting a current-based model. Our proposed model releases the constraint of the nearly constant membrane potential. We confirm that the obtained model is reducible to the previous model in the non-firing situation and that it reproduces the temporal mean values and relative power spectrum densities of the average membrane potentials for the spiking neurons. It is further ensured that the existing NMM properly models the averaged dynamics over individual neurons even if they are spiking in the populations.

Facilitated lexical ambiguity processing by transcranial direct current stimulation over the left inferior frontal cortex.

Previous studies suggest that the left inferior frontal cortex is involved in the resolution of lexical ambiguities for language comprehension. In this study, we hypothesized that processing of lexical ambiguities is improved when the excitability of the left inferior frontal cortex is enhanced. To test the hypothesis, we conducted an experiment with transcranial direct current stimulation (tDCS). We investigated the effect of anodal tDCS over the left inferior frontal cortex on behavioral indexes for semantic judgment on lexically ambiguous and unambiguous words within a context. Supporting the hypothesis, the RT was shorter in the anodal tDCS session than in the sham session for ambiguous words. The results suggest that controlled semantic retrieval and contextual selection were facilitated by anodal tDCS over the left inferior frontal cortex.

Phase shifts in alpha-frequency rhythm detected in electroencephalograms influence reaction time.

Although the phase shifts in ongoing oscillations seen in electroencephalograms (EEGs) and magnetoencephalograms are an important factor in discussions of phase dynamics, such as synchrony and reset, few studies have focused specifically on the phase shift. Here we investigate the relationship between phase shifts in alpha-frequency rhythms and reaction times during a visual simple reaction task by applying our previously described method (Naruse et al., 2013), which enables detection of phase shifts from a single EEG trial. In the left, parietal, and occipital areas, the reaction times in the trials in which phase shifts were detected before the button press were significantly longer than in those in which phase shifts were not so detected. These results indicate that phase shifts in the alpha and mu rhythms relate to variability in reaction times.

Accuracy of estimating strengths of dipole moments from a small number of magnetoencephalographic trial data.

The conventional analysis estimates both the locations and strengths of neural source activations from event-related magnetoencephalography data that are averaged across about a hundred trials. In the present report, we propose a new method based on a minimum modified-l 1-norm to obtain the dependence of strengths on the presented stimuli from a limited number of trial data. It estimates the strengths from 10-trial average data and the locations from 100-trial average data. The method can be applied to neural activations whose strengths, but not locations, depend on the presented stimuli. For instance, it can be used in experiments in which the activation in the anterior temporal area (aT) is measured by varying semantic relatedness between stimuli in linguistic experiments. We conducted a realistic simulation, following previous experiments on lexico-semantic processing, in which five neural sources were simultaneously activated. The results showed that when the signal-to-noise ratio was one for non-averaged data, the proposed method had standard deviations of 13 % for the normalized strengths in the aT. It is inferred on the basis of the general linear model in which the strength has a linear dependence on the stimulus parameters that the proposed method can detect the dependence at a significance level of 1 % if the peak-to-peak change in normalized strength is more than 49 %. It is smaller than 66 % for the conventional method, which estimated locations and strengths from 10-trial data for each point. Thus, the proposed method can plot an activation-strength versus stimulus-parameter curve with better sensitivity.

Supramolecular photocyclodimerization of 2-hydroxyanthracene with a chiral hydrogen-bonding template, cyclodextrin and serum albumin.

2-Hydroxyanthracene (HA) in its neutral form smoothly photocyclodimerized to four stereoisomeric [4 + 4]-cyclodimers, which were isolated and characterized for the first time, whereas the anionic form of HA turned out to be photochemically inert. Enantiodifferentiating photocyclodimerization of HA in the presence of a chiral hydrogen-bonding template (TKS159), γ-cyclodextrin (γ-CDx) and bovine serum albumin (BSA) was examined to afford chiral syn-head-to-tail and anti-head-to-head cyclodimers in modest enantiomeric excesses with TKS159 and γ-CDx, but practically no photocyclodimerization proceeded in the presence of BSA probably due to the ionization of HA in the binding sites.

Statistical method for detecting phase shifts in alpha rhythm from human electroencephalogram data.

We developed a statistical method for detecting discontinuous phase changes (phase shifts) in fluctuating alpha rhythms in the human brain from electroencephalogram (EEG) data obtained in a single trial. This method uses the state space models and the line process technique, which is a Bayesian method for detecting discontinuity in an image. By applying this method to simulated data, we were able to detect the phase and amplitude shifts in a single simulated trial. Further, we demonstrated that this method can detect phase shifts caused by a visual stimulus in the alpha rhythm from experimental EEG data even in a single trial. The results for the experimental data showed that the timings of the phase shifts in the early latency period were similar between many of the trials, and that those in the late latency period were different between the trials. The conventional averaging method can only detect phase shifts that occur at similar timings between many of the trials, and therefore, the phase shifts that occur at differing timings cannot be detected using the conventional method. Consequently, our obtained results indicate the practicality of our method. Thus, we believe that our method will contribute to studies examining the phase dynamics of nonlinear alpha rhythm oscillators.

Cross- versus homo-photocyclodimerization of anthracene and 2-anthracenecarboxylic acid mediated by a chiral hydrogen-bonding template. Factors controlling the cross-/homo-selectivity and enantioselectivity.

Competitive cross-/homo-photocyclodimerization of anthracene (AN) and 2-anthracenecarboxylic acid (AC) mediated by a chiral hydrogen-bonding template (TKS) was investigated under various conditions. The cross-photocyclodimerization was favored by a factor of 4-5 at all temperatures and wavelengths examined to afford the AC-AN cross-dimer in 80-84% yield even at AN/AC = 1 and in 98% yield at AN/AC = 10. The enantiomeric excesses (ee's) obtained were 27-47% for the homo-dimers and 21-24% for the cross-dimer. The absolute configuration of the cross-dimer was determined by comparing the experimental and theoretical circular dichroism spectra and further correlated with the re/si enantiotopic-face selectivity upon AC-TKS complexation in the ground state. Detailed analyses of the complexation behavior and the fluorescence lifetime and cyclodimerization rate of excited re/si complexes revealed that the product's ee is critically controlled not only by the relative abundance of the re/si complexes in the ground and excited states but also by their relative photocyclodimerization rate. Crucially, the ground-state thermodynamics and the excited-state kinetics are not synergistic but offsetting in enantiotopic-face selectivity, and the latter overwhelms the former to give the homo- and cross-dimers in modest ee's. Finally, some practical strategies for enhancing the enantioselectivity in chiral template-mediated photochirogenesis have been proposed.

Language comprehension dependent on emotional context: a magnetoencephalography study.

In communication, language can be interpreted differently depending upon the emotional context. To clarify the effect of emotional context on language processing, we performed experiments using a cross-modal priming paradigm with an auditorily presented prime and a visually presented target. The primes were the names of people that were spoken with a happy, sad, or neutral intonation; the targets were interrogative one-word sentences with emotionally neutral content. Using magnetoencephalography, we measured neural activities during silent reading of the targets presented in a happy, sad, or neutral context. We identified two conditional differences: the happy and sad conditions produced less activity than the neutral condition in the right posterior inferior and middle frontal cortices in the latency window from 300 to 400 ms; the happy and neutral conditions produced greater activity than the sad condition in the left posterior inferior frontal cortex in the latency window from 400 to 500 ms. These results suggest that the use of emotional context stored in the right frontal cortex starts at ∼300 ms, that integration of linguistic information with emotional context starts at ∼400 ms in the left frontal cortex, and that language comprehension dependent on emotional context is achieved by ∼500 ms.