Biology subjects

Rodriguez Larios, J.

Publications and source records attributed to Rodriguez Larios, J..

7 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↗

bioRxiv2026

Not all mantra meditations are equal: Emergence of divergent alpha oscillatory dynamics across mantras

The study of contemplative practices has evolved into a mature field, yet current taxonomies tend to classify all mantra-based meditation approaches as a single category, overlooking potentially different neural states induced by different mantras or different instructions. To address this gap, we conducted a study of 50 novice subjects practicing two types of mantra-based meditation over a six week period to evaluate changes in Electroencephalography (EEG) during and after meditation. Participants were randomly assigned to meditating with the Hare Krishna (HK) and Sa-Ta-Na-Ma (SA) mantras. Using spectral parameterization, we assessed the effects of each type of meditation on individual alpha power (IAP), individual alpha frequency (IAF) and center of gravity (CoG). The results revealed marked differences in alpha dynamics between the two practices. On the one hand, the HK group exhibited widespread IAP decrease and an IAF/CoG increase during mantra meditation that was maintained during rest after the meditation, which became more pronounced after training in the HK meditation. On the other hand, the SA group showed a localized IAP reduction during meditation and significant reduction of IAF during meditation after training. We suggest that the higher cognitive demands of HK induce a more activating, attentionally focused state, whereas SA promotes a more relaxed state. Additional psychological data show that both meditation groups had reduction in stress. Thus, these findings challenge the monolithic classification of mantra meditation and highlight the importance of differentiating practices according to their mechanisms, particularly for their targeted application in mental health contexts.

neuroscience↗

bioRxiv2025

Revisiting alpha-theta cross-frequency dynamics during working memory

Prior Electroencephalography (EEG) research has shown that during working memory delay, alpha (8-14 Hz) and theta (4-8 Hz) oscillations tend to form a 2:1 frequency ratio. According to the Binary Hierarchy Brain Body Oscillation Theory (BHBBOT), a recent model grounded in mathematical analysis, such harmonic (2:1) alpha:theta frequency configurations reflect enhanced connectivity between brain regions generating these rhythms. However, this prediction has not yet been empirically tested. In this study, we leveraged Information Theory and the Theory of Weakly Coupled Oscillators (TWCO) to examine whether the previously observed frequency modulations in alpha and theta rhythms during working memory are accompanied by changes in inter-areal connectivity. Contrary to the BHBBOT predictions, both Information Theory metrics and TWCO parameters showed that connectivity between frontal theta and parietal alpha rhythms was significantly reduced during the working-memory delay period (while the proportion of 2:1 ratios increased). In addition, phase locking value, a standard measure of synchrony, was also significantly reduced during working memory delay and was negatively associated with behavioural performance. In conclusion, our results show that the increased occurrence of 2:1 alpha:theta cross-frequency ratios during working memory reflects functional segregation (rather than integration) between frontal and parietal regions.

neuroscience↗

bioRxiv2025

Reduced occurrence of alpha waves during resting state predicts high ADHD traits in young adults

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental condition with significant cognitive and social impacts. Identifying reliable biomarkers for ADHD is crucial for developing personalized therapies. Electroencephalography (EEG) alpha oscillations (8-12 Hz) have been suggested as a potential biomarker, but findings have been inconsistent. This study aimed to investigate whether alpha oscillations in young adulthood are associated with high ADHD traits using EEG data from a large twin sample (N = 556) enriched with participants with ADHD and autism. We assessed whether alpha oscillations during rest were associated with high ADHD traits through logistic regression analysis. In addition, we used twin modelling to estimate the heritability of EEG alpha measures and their relationship with ADHD traits. Results showed that relative alpha power was a significant predictor of ADHD traits when controlling for other factors such as age, sex and autistic traits. Specifically, we found that for each unit decrease in relative alpha power, the likelihood of being in the high ADHD trait group increased by approximately 26%. Further analysis suggested that group differences were due to a reduced occurrence (but not amplitude) of oscillatory bursts in the alpha range. Finally, our twin modelling results suggested that although alpha power is heritable, the genetic factors contributing to individual differences in alpha measures and ADHD traits were largely independent. Together, these findings suggest that reduced alpha oscillations, particularly occurrence of alpha bursts, may serve as a potential biomarker for ADHD. Our results may have implications for neuromodulation therapies targeting alpha rhythms in ADHD, such as neurofeedback and transcranial alternating current stimulation (tACS).

neuroscience↗

bioRxiv2024

Common neural mechanisms supporting time judgements in humans and monkeys

There has been an increasing interest in identifying the biological underpinnings of human time perception, for which purpose research in non-human primates (NHP) is common. Although previous work, based on behaviour, suggests that similar mechanisms support time perception across species, the neural correlates of time estimation in humans and NHP have not been directly compared. In this study, we assess whether brain evoked responses during a time categorization task are similar across species. Specifically, we assess putative differences in post-interval evoked potentials as a function of perceived duration in human EEG (N = 24) and local field potential (LFP) and spike recordings in pre-supplementary motor area (pre-SMA) of one monkey. Event-related potentials (ERPs) differed significantly after the presentation of the temporal interval between "short" and "long" perceived durations in both species, even when the objective duration of the stimuli was the same. Interestingly, the polarity of the reported ERPs was reversed for incorrect trials (i.e., the ERP of a "long" stimulus looked like the ERP of a "short" stimulus when a time categorization error was made). Hence, our results show that post-interval potentials reflect the perceived (rather than the objective) duration of the presented time interval in both NHP and humans. In addition, firing rates in monkeys pre-SMA also differed significantly between short and long perceived durations and were reversed in incorrect trials. Together, our results show that common neural mechanisms support time categorization in NHP and humans, thereby suggesting that NHP are a good model for investigating human time perception.

neuroscience↗

bioRxiv2024

Assessing the effects of an 8-week mindfulness training program on neural oscillations and self-reports during meditation practice

Previous literature suggests that mindfulness meditation can have positive effects on mental health, however, its mechanisms of action are still unclear. In this pre-registered study, we investigate the effects of mindfulness training on lapses of attention (and their associated neural correlates) during meditation practice. For this purpose, we recorded Electroencephalogram (EEG) during meditation practice before and after 8 weeks of mindfulness training (or waitlist) in 41 participants (21 treatment and 20 controls). In order to detect lapses of attention and characterize their EEG correlates, we interrupted participants during meditation to report their level of focus and drowsiness. First, we show that self-reported lapses of attention during meditation practice were associated to an increased occurrence of theta oscillations (3-6 Hz), which were slower in frequency and more spatially widespread than theta oscillations occurring during focused attention states. Then, we show that mindfulness training did not reduce the occurrence of lapses of attention nor their associated EEG correlate (i.e. theta oscillations) during meditation. Instead, we find that mindfulness training was associated with a significant slowing of alpha oscillations in frontal electrodes during meditation. Crucially, frontal alpha slowing during meditation practice has been reported in highly experienced meditators and is thought to reflect relative decreases in arousal levels. Together, our findings provide insights into the EEG correlates of mindfulness meditation, which could have important implications for the identification of its mechanisms of action and/or the development of neuromodulation protocols aimed at facilitating meditation practice.

neuroscience↗

bioRxiv2022

Visual working memory recruits two functionally distinct alpha rhythms in posterior cortex

Oscillatory activity in the human brain is dominated by posterior alpha oscillations (8-14 Hz), which have been shown to be functionally relevant in a wide variety of cognitive tasks. Although posterior alpha oscillations are commonly considered a single oscillator anchored at an individual alpha frequency (IAF; [~]10 Hz), previous work suggests that IAF reflects a spatial mixture of different brain rhythms. In this study, we assess whether Independent Component Analysis (ICA) can disentangle functionally distinct posterior alpha rhythms in the context of visual short-term memory retention. Magnetoencephalography (MEG) was recorded in 33 subjects while performing a visual working memory task. Group analysis at sensor level suggested the existence of a single posterior alpha oscillator that increases in power and decreases in frequency during memory retention. Conversely, single-subject analysis of independent components revealed the existence of two dissociable alpha rhythms: one that increases in power during memory retention (Alpha1) and another one that decreases in power (Alpha2). Alpha1 and Alpha2 rhythms were differentially modulated by the presence of visual distractors (Alpha1 increased in power while Alpha2 decreased) and had an opposite relationship with accuracy (positive for Alpha1 and negative for Alpha2). In addition, Alpha1 rhythms showed a lower peak frequency, a narrower peak width, a greater relative peak amplitude and a more central source than Alpha2 rhythms. Together, our results demonstrate that modulations in posterior alpha oscillations during short-term memory retention reflect the dynamics of at least two distinct brain rhythms with different functions and spatiospectral characteristics. Significance statementAlpha oscillations are the most prominent feature of the human brains electrical activity, and consist of rhythmic neuronal activity in posterior parts of the cortex. Alpha is usually considered a single brain rhythm that changes in power and frequency to support cognitive operations. We here show that posterior alpha entails at least two dissociable rhythms with distinct functions and characteristics. These findings could solve previous inconsistencies in the literature regarding the direction of task-related alpha power/frequency modulations and their relation to cognitive performance. In addition, the existence of two distinct posterior alpha rhythms could have important consequences for the design of neurostimulation protocols aimed at modulating alpha oscillations and subsequently cognition.

neuroscience↗