Behavioral rhythms synchronize between humans for communication; however, the relationship of brain rhythm synchronization during speech rhythm synchronization between individuals remains unclear. Here, we conducted alternating speech tasks in which two subjects alternately pronounced letters of the alphabet during hyperscanning electroencephalography. Twenty pairs of subjects performed the task before and after each subject individually performed the task with a machine that pronounced letters at almost constant intervals. Speech rhythms were more likely to become synchronized in human–human tasks than human–machine tasks. Moreover, theta/alpha (6–12 Hz) amplitudes synchronized in the same temporal and lateral-parietal regions in each pair. Behavioral and inter-brain synchronizations were enhanced after human–machine tasks. These results indicate that inter-brain synchronizations are tightly linked to speech synchronizations between subjects. Furthermore, theta/alpha inter-brain synchronizations were also found in subjects while they observed human–machine tasks, which suggests that the inter-brain synchronization might reflect empathy for others' speech rhythms.

Working memory (WM) tasks require not only distinct functions such as a storage buffer and central executive functions, but also coordination among these functions. Neuroimaging studies have revealed the contributions of different brain regions to different functional roles in WM tasks; however, little is known about the neural mechanism governing their coordination. Electroencephalographic (EEG) rhythms, especially theta and alpha, are known to appear over distributed brain regions during WM tasks, but the rhythms associated with task‐relevant regional coupling have not been obtained thus far. In this study, we conducted time–frequency analyses for EEG data in WM tasks that include manipulation periods and memory storage buffer periods. We used both auditory WM tasks and visual WM tasks. The results successfully demonstrated function‐specific EEG activities. The frontal theta amplitudes increased during the manipulation periods of both tasks. The alpha amplitudes increased during not only the manipulation but also the maintenance periods in the temporal area for the auditory WM and the parietal area for the visual WM. The phase synchronization analyses indicated that, under the relevant task conditions, the temporal and parietal regions show enhanced phase synchronization in the theta bands with the frontal region, whereas phase synchronization between theta and alpha is significantly enhanced only within the individual areas. Our results suggest that WM task‐relevant brain regions are coordinated by distant theta synchronization for central executive functions, by local alpha synchronization for the memory storage buffer, and by theta–alpha coupling for inter‐functional integration.

Fifty-seven years after NO_x (NO + NO₂) were identified as essential components of photochemical smog, atmospheric chemical models fail to correctly predict •OH/HO₂• concentrations under NO_x-rich conditions. This deficiency is due, in part, to the uncertain rates and mechanism for the reactive dissolution of NO₂(g) (2NO₂ + H₂O = NO₃⁻ + H⁺ + HONO) in fog and aerosol droplets. Thus, state-of-the-art models parametrize the uptake of NO₂ by atmospheric aerosol from data obtained on “deactivated tunnel wall residue”. Here, we report experiments in which NO₃⁻ production on the surface of microdroplets exposed to NO₂(g) for ∼1 ms is monitored by online thermospray mass spectrometry. NO₂ does not dissolve in deionized water (NO₃⁻ signals below the detection limit) but readily produces NO₃⁻ on aqueous NaX (X = Cl, Br, I) microdroplets with NO₂ uptake coefficients γ that vary nonmonotonically with electrolyte concentration and peak at γ_max ∼ 10⁻⁴ for [NaX] ∼ 1 mM, which is >10³ larger than that in neat water. Since I⁻ is partially oxidized to I₂^•− in this process, anions seem to capture NO₂(g) into X−NO₂^•− radical anions for further reaction at the air/water interface. By showing that γ is strongly enhanced by electrolytes, these results resolve outstanding discrepancies between previous measurements in neat water versus NaCl-seeded clouds. They also provide a general mechanism for the heterogeneous conversion of NO₂(g) to (NO₃⁻ + HONO) on the surface of aqueous media.

Replacing platinum by a less precious metal such as palladium, is highly desirable for lowering the cost of fuel-cell electrocatalysts. However, the instability of palladium in the harsh environment of fuel-cell cathodes renders its commercial future bleak. Here we show that by incorporating trace amounts of gold in palladium-based ternary (Pd₆CoCu) nanocatalysts, the durability of the catalysts improves markedly. Using aberration-corrected analytical transmission electron microscopy in conjunction with synchrotron X-ray absorption spectroscopy, we show that gold not only galvanically replaces cobalt and copper on the surface, but also penetrates through the Pd–Co–Cu lattice and distributes uniformly within the particles. The uniform incorporation of Au provides a stability boost to the entire host particle, from the surface to the interior. The spontaneous replacement method we have developed is scalable and commercially viable. This work may provide new insight for the large-scale production of non-platinum electrocatalysts for fuel-cell applications.

Human daily behaviors are often affected by subjective preferences. Studies have shown that physical responses are affected by unconscious preferences before conscious decision making. Accordingly, attention-related neural activities could be influenced by unconscious preferences. However, few neurological data exist on the relationship between visual attention and subjective preference. To address this issue, we focused on lateralization during visual attention and investigated the effects of subjective color preferences on visual attention-related brain activities. We recorded electroencephalograph (EEG) data during a preference judgment task that required 19 participants to choose their preferred color from 2 colors simultaneously presented to the right and left hemifields. In addition, to identify oscillatory activity during visual attention, we conducted a control experiment in which the participants focused on either the right or the left color without stating their preference. The EEG results showed enhanced theta (4-6 Hz) and decreased alpha (10-12 Hz) activities in the right and left occipital electrodes when the participants focused on the color in the opposite hemifield. Occipital theta synchronizations also increased contralaterally to the hemifield to which the preferred color was presented, whereas the alpha desynchronizations showed no lateralization. The contralateral occipital theta activity lasted longer than the ipsilateral occipital theta activity. Interestingly, theta lateralization was observed even when the preferred color was presented to the unattended side in the control experiment, revealing the strength of the preference-related theta-modulation effect irrespective of visual attention. These results indicate that subjective preferences modulate visual attention-related brain activities.

Visual working memory (VWM) capacity is affected by motivational influences; however, little is known about how reward-related brain activities facilitate the VWM systems. To investigate the dynamic relationship between VWM- and reward-related brain activities, we conducted time–frequency analyses using electroencephalograph (EEG) data obtained during a monetary-incentive delayed-response task that required participants to memorize the position of colored disks. In case of a correct answer, participants received a monetary reward (0, 10 or 50 Japanese yen) announced at the beginning of each trial. Behavioral results showed that VWM capacity under high-reward condition significantly increased compared with that under low- or no-reward condition. EEG results showed that frontal theta (6 Hz) amplitudes enhanced during delay periods and positively correlated with VWM capacity, indicating involvement of theta local synchronizations in VWM. Moreover, frontal beta activities (24 Hz) were identified as reward-related activities, because delay-period amplitudes correlated with increases in VWM capacity between high-reward and no-reward conditions. Interestingly, cross-frequency couplings between frontal theta and beta phases were observed only under high-reward conditions. These findings suggest that the functional dynamic linking between VWM-related theta and reward-related beta activities on the frontal regions plays an integral role in facilitating increases in VWM capacity.