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The coupling of gamma oscillation (~ 40+ Hz) amplitude to the phase of ongoing theta (~ 6 Hz) oscillations has been proposed to be directly relevant for memory performance. Current theories suggest that memory capacity scales with number of gamma cycles that can be fitted into the preferred phase of a theta cycle. Following this logic, transcranial alternating current stimulation (tACS) may be used to adjust theta cycles (increasing/decreasing theta frequency) to decrease or increase memory performance during stimulation. Here, we used individualized EEG-informed theta tACS to (1) experimentally "slow down" individual theta frequency (ITF), (2) evaluate cognitive after effects on a battery of memory and learning tasks, and (3) link the cognitive performance changes to tACS-induced effects on theta-band oscillations as measured by post EEG. We found frequency- and task-specific tACS after effects demonstrating a specific enhancement in memory capacity. This tACS-induced cognitive enhancement was specific to the visual memory task performed immediately after tACS offset, and specific to the ITF-1 Hz (slowing) stimulation condition and thus following a protocol specifically designed to slow down theta frequency to enhance memory capacity. Follow-up correlation analyses in this group linked the enhanced memory performance to increased left frontal-parietal theta-band connectivity. Interestingly, resting-state theta power immediately after tACS offset revealed a theta power increase not for the ITF-1 Hz group, but only for the ITF group where the tACS frequency was 'optimal' for entrainment. These results suggest that while individually calibrated tACS at peak frequency maximally modulates resting-state oscillatory power, tACS stimulation slightly below this optimal peak theta frequency is better suited to enhance memory capacity performance. Importantly, our results further suggest that such cognitive enhancement effects can last beyond the period of stimulation and are linked to increased network connectivity, opening the door towards more clinical and applied relevance of using tACS in cognitive rehabilitation and/or neurocognitive enhancement. [ABSTRACT FROM AUTHOR]

Despite the widespread use of the SH-SY5Y human neuroblastoma cell line in modeling human neurons in vitro, protocols for growth, differentiation and experimentation differ considerably across the literature. Many studies fully differentiate SH-SY5Y cells before experimentation, to investigate plasticity measures in a mature, human neuronal-like cell model. Prior to experimentation, serum is often removed from cell culture media, to arrest the cell growth cycle and synchronize cells. However, the exact effect of this serum removal before experimentation on mature, differentiated SH-SY5Y cells has not yet been described. In studies using differentiated SH-SY5Y cells, any effect of serum removal on plasticity markers may influence results. The aim of the current study was to systematically characterize, in differentiated, neuronal-like SH-SY5Y cells, the potentially confounding effects of complete serum removal in terms of morphological and gene expression markers of plasticity. We measured changes in commonly used morphological markers and in genes related to neuroplasticity and synaptogenesis, particularly in the BDNF-TrkB signaling pathway. We found that complete serum removal from already differentiated SH-SY5Y cells increases neurite length, neurite branching, and the proportion of cells with a primary neurite, as well as proportion of βIII-Tubulin and MAP2 expressing cells. Gene expression results also indicate increased expression of PSD95 and NTRK2 expression 24 h after serum removal. We conclude that serum deprivation in differentiated SH-SY5Y cells affects morphology and gene expression and can potentially confound plasticity-related outcome measures, having significant implications for experimental design in studies using differentiated SH-SY5Y cells as a model of human neurons. [ABSTRACT FROM AUTHOR]

Animal models, human neuroimaging and lesion studies revealed that the gut microbiota can influence the interaction between the central and the enteric nervous systems via the gut–brain axis (GBA) and can affect brain regions linked to basic emotional and cognitive processes. The role of the gut microbiota in decision-making in healthy humans thus far remains largely unknown. Our study establishes a functional relationship between the gut microbiota and healthy humans' decisions that involve risk and time. We conducted a between subjects' placebo-controlled double-blinded design, with two groups and two sessions separated by 28 days, during which participants received daily doses of probiotics or a placebo. We investigated whether the prolonged and controlled intake of probiotics affects risk-taking behavior and intertemporal choices using incentivized economic tasks. We found a significant decrease in risk-taking behavior and an increase in future-oriented choices in the probiotics group as compared to the placebo group. These findings provide the first direct experimental evidence suggesting a potential functional role on the part of the microbiota-gut-brain axis in decision-making, creating a path for potential clinical applications and allowing for a better understanding of the underlying neural mechanisms of risk-taking behavior and intertemporal choices. [ABSTRACT FROM AUTHOR]

Rhythmic stimulation can be applied to modulate neuronal oscillations. Such 'entrainment' is optimized when stimulation frequency is individually calibrated based on magneto/encephalography markers. It remains unknown how consistent such individual markers are across days/sessions, within a session, or across cognitive states, hemispheres and estimation methods, especially in a realistic, practical, lab setting. We here estimated individual alpha frequency (IAF) repeatedly from short electroencephalography (EEG) measurements at rest or during an attention task (cognitive state), using single parieto‐occipital electrodes in 24 participants on 4 days (between‐sessions), with multiple measurements over an hour on 1 day (within‐session). First, we introduce an algorithm to automatically reject power spectra without a sufficiently clear peak to ensure unbiased IAF estimations. Then we estimated IAF via the traditional 'maximum' method and a 'Gaussian fit' method. IAF was reliable within‐ and between‐sessions for both cognitive states and hemispheres, though task‐IAF estimates tended to be more variable. Overall, the 'Gaussian fit' method was more reliable than the 'maximum' method. Furthermore, we evaluated how far from an approximated 'true' task‐related IAF the selected 'stimulation frequency' was, when calibrating this frequency based on a short rest‐EEG, a short task‐EEG, or simply selecting 10 Hz for all participants. For the 'maximum' method, rest‐EEG calibration was best, followed by task‐EEG, and then 10 Hz. For the 'Gaussian fit' method, rest‐EEG and task‐EEG‐based calibration were similarly accurate, and better than 10 Hz. These results lead to concrete recommendations about valid, and automated, estimation of individual oscillation markers in experimental and clinical settings. [ABSTRACT FROM AUTHOR]

Recent evidence suggests that visuospatial attentional performance is not stable over time but fluctuates in a rhythmic fashion. These attentional rhythms allow for sampling of different visuospatial locations in each cycle of this rhythm. However, it is still unclear in which paradigmatic circumstances rhythmic attention becomes evident. First, it is unclear at what spatial locations rhythmic attention occurs. Second, it is unclear how the behavioural relevance of each spatial location determines the rhythmic sampling patterns. Here, we aim to elucidate these two issues. Firstly, we aim to find evidence of rhythmic attention at the predicted (i.e. cued) location under moderately informative predictor value, replicating earlier studies. Secondly, we hypothesise that rhythmic attentional sampling behaviour will be affected by the behavioural relevance of the sampled location, ranging from non‐informative to fully informative. To these aims, we used a modified Egly‐Driver task with three conditions: a fully informative cue, a moderately informative cue (replication condition), and a non‐informative cue. We did not find evidence of rhythmic sampling at cued locations, failing to replicate earlier studies. Nor did we find differences in rhythmic sampling under different predictive values of the cue. The current data does not allow for robust conclusions regarding the non‐cued locations due to the absence of a priori hypotheses. Post‐hoc explorative data analyses, however, clearly indicate that attention samples non‐cued locations in a theta‐rhythmic manner, specifically when the cued location bears higher behavioural relevance than the non‐cued locations. [ABSTRACT FROM AUTHOR]

Sexual responding in transgender people has typically been investigated from a medical and functional perspective. Aligning with the biopsychosocial model, it is however equally important to consider psychological aspects of sexuality in this population. We propose that the Sexual Self-Concept (SSC) theory offers a valuable framework to understand (sexual) wellbeing in transgender people, while Self-Concept Discrepancy (SCD) theory could offer an explanation of the mechanisms underlying negative SSCs related to gender dysphoria. We investigated differences in SSC (consisting of sexual esteem, sexual attitudes, and sexual self-efficacy) in 197 binary transgender and 205 cisgender individuals using an online survey and explored the mediating role of actual/ideal self-discrepancies in explaining the relation between gender dysphoria and SSC. Transgender and cisgender individuals differed significantly in seven out of eight components related to sexual esteem and sexual attitudes. Actual/ideal self-discrepancies mediated the relationship between gender dysphoria and the SSC in transgender individuals for the sexual esteem components related to body perception, conduct, and attractiveness, as well as for sexual anxiety. We found no relation between gender dysphoria and the other SSC components in this group. We conclude that SSC discrepancies could be a valuable treatment target to improve transgender individuals' sexual esteem and sexual attitudes. [ABSTRACT FROM AUTHOR]