Biology subjects

Carrasco-Gomez, M.

Publications and source records attributed to Carrasco-Gomez, M..

4 recordsLinked to original sources

bioRxiv2024

Individual alpha frequency tACS reduces functional connectivity across the default mode network

Structured AbstractO_ST_ABSObjectivesC_ST_ABSResearch on the influence of transcranial alternating current stimulation over alpha functional connectivity (FC) is scarce, and at the same time poses as a potential treatment for various diseases. This study aimed to investigate the effects of individualized alpha frequency tACS (IAF-tACS) on FC within the default mode network (DMN) in healthy individuals, particularly focusing on the precuneus (PCU) as a major hub within the network. Materials and Methods27 healthy participants were recruited, which underwent a 20-minute IAF-tACS session and three magnetoencephalography (MEG) recordings: two pre-stimulation and one post-stimulation. Participants were randomly assigned to either the stimulation or sham group. FC was evaluated through the corrected imaginary phase locking value (ci-PLV) and leakage corrected amplitude envelope correlation (AEC-c). Statistical analyses compared both Pre-Post FC ratio between groups through ratio t-tests and intragroup FC changes through repeated measures t-tests, with FDR correction applied to account for multiple comparisons. An additional analysis simulated the influence of the cortical folding on the effect of tACS over FC. ResultsIAF-tACS significantly decreased AEC-c within the PCU and DMN in the stimulation group compared to the sham group, especially influencing antero-posterior links between hubs of the DMN. No significant changes were observed in ci-PLV connectivity metrics. Negative correlations were found between AEC-c FC changes and power alterations in posterior DMN areas, suggesting a complex interaction between cortical folding and electric field direction. ConclusionsAgainst our initial hypothesis, IAF-tACS reduced FC in the DMN, possibly due to phase disparities introduced by cortical gyrification. These findings suggest that tACS might modulate FC in a more complex manner than previously thought, highlighting the need for further research into the personalized application of neuromodulation techniques, as well as its potential therapeutic implications for conditions like Alzheimers disease.

neuroscience↗

bioRxiv2024

Dynamic functional connectivity is modulated by the amount of p-Tau231 in blood in cognitively intact participants

INTRODUCTIONElectrophysiology and plasma biomarkers are early and non-invasive candidates for Alzheimers disease detection. The purpose of this paper is to evaluate changes in dynamic functional connectivity measured with magnetoencephalography, associated with the plasma pathology marker p-tau231 in unimpaired adults. METHODS73 individuals were included. Static and dynamic functional connectivity were calculated using leakage corrected amplitude envelope correlation. Each sources strength entropy across trials was calculated. A data-driven statistical analysis was performed to find the association between functional connectivity and plasma p-tau231 levels. Regression models were used to assess the influence of other variables over the clusters connectivity. RESULTSFrontotemporal dynamic connectivity positively associated with p-tau231 levels. Linear regression models identified pathological, functional and structural factors that influence dynamic functional connectivity. DISCUSSIONThese results expand previous literature on dynamic functional connectivity in healthy individuals at risk of AD, highlighting its usefulness as an early, non-invasive and more sensitive biomarker.

neuroscience↗

bioRxiv2024

Dynamics of Brain Connectivity across the Alzheimer's Disease Spectrum: a magnetoencephalography study

Alzheimers disease (AD) represents a major challenge in neurodegenerative disease research, as it is characterized by a complex pathophysiology that involves not only structural but also functional changes in the brain. While changes in static functional connectivity have already been linked to AD, there is still a lack of research studying dynamic functional connectivity (dFC) across the AD continuum, which could be crucial for identifying potential biomarkers for early diagnosis and tracking disease progression. This study leverages the high temporal resolution of MEG to dissect the dynamics of brain connectivity alterations across various stages of AD and their association with cognitive decline and structural brain changes. 321 participants were included in this study, categorized into healthy control, subjective cognitive decline (SCD), and mild cognitive impairment (MCI) groups. Amplitude envelope correlation with leakage correction was calculated over MEG signals using a sliding window, and the correlation across epochs was studied to assess dFC at whole-brain and node level. Finally, we explored dFC associations with cognitive scores, grey matter volume, and white matter fractal anisotropy. The study unveils a significant reduction in whole-brain dFC, especially within the alpha and beta frequency bands, as individuals advance along the AD continuum. Notably, the frontal and temporal lobes, as well as regions within the default mode network, exhibited pronounced dFC reductions. Finally, dFC significantly correlated with cognitive performance and changes in structural brain, suggesting the potential of the proposed dFC metric as sensitive indicator for monitoring disease progression. This investigation provides crucial insights into the temporal dynamics of brain connectivity alterations in the early stages of the AD spectrum, underlining the importance of dFC changes as reflective of cognitive and anatomical degeneration. The findings hint towards a strong relationship between connectivity profiles and white matter integrity, especially for high frequency activity in the association cortices. Key PointsO_LIDynamic functional connectivity declines over the AD spectrum. C_LIO_LIDynamic functional connectivity reductions are most prominent in orbitofrontal, temporal, and DMN-related areas. C_LIO_LICognitive performance, brain volumetrics, and white matter integrity parameters positively correlate with dynamic functional connectivity over the whole AD spectrum, and most significantly among mild cognitive impairment participants. C_LI

neuroscience↗

bioRxiv2024

Effects of Alzheimer's disease plasma marker levels on multilayer centrality in healthy individuals

Finding early and non-invasive biomarkers that help identify individuals in the earliest stages of the Alzheimers disease continuum is paramount. Electrophysiology and plasma biomarkers are great candidates in this pursuit. Furthermore, the combination of functional connectivity metrics with graph-theory analyses allows for a deeper understanding of network alterations. Despite this, this is the first MEG study to assess multilayer centrality considering inter-band connectivity in an unimpaired population at high risk of Alzheimers disease. Our objective is twofold. First, to address the relationship between a compound centrality score designed to overcome previous inconsistencies stemming from the use of various individual metrics, and plasma pathology markers of Alzheimers disease in unimpaired individuals with elevated levels of the latter. Lastly, to evaluate whether hubs centrality is more affected by the pathology. 33 individuals with available MEG recordings and elevated plasma pathology markers were included. A compound centrality score for each brain source of every subject was calculated combining widely used centrality metrics, considering intra- and inter-band connections. Spearman correlations were carried out to address the association between each nodes centrality score and biomarkers levels. Next, to test whether greater associations were found in hubs, a correlation between the obtained rho and the grand-average of the centrality score was carried out. Increasing concentrations of p-tau231 were associated with greater centrality within the network of posterior areas, which increased their connectedness in the theta range with the remaining areas, regardless of the latters frequency range. The opposite relationship was found for left areas, that decreased their connectedness in the gamma frequency range. Hubs centrality was significantly more affected by p-tau231 levels. Our results expand previous literature demonstrating early network reorganizations associated with elevated plasma p-tau231 in cognitively unimpaired individuals. Multilayer centrality increases in the theta band in posterior regions are congruent with previous results and theoretical models, that predict a longitudinal evolution towards a loss of centrality. On the other hand, the changes in multilayer centrality found in the gamma band could be associated with inhibitory neuron dysfunction, classical in AD pathology. Lastly, hubs were more likely to increase their centrality in association to p-tau231, thus corroborating hubs vulnerability.

neuroscience↗