bioRxiv Science⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2023.09.16.557985

Interaction between task-evoked and spontaneous brain activities: Insights from two event-related fMRI studies

Nayak, S.·Hojjati, S. H.·Ozoria-Blake, S.·Feiz, F.·Shteingart, J.·Guerrero, A. F.·Razlighi, Q. R.
View original source ↗Export metadata ↓

Abstract

Human brain activities measured by fMRI can be categorized into at least two distinct categories; 1) spontaneous: slow (< 0.1 Hz) but inter-regionally coherent fluctuations in MR signal, and 2) task-evoked: change in the MR signal due to external stimulation. To date, there is no consensus in the field about the roles of spontaneous brain activity and whether it interacts with task-evoked activity. This is mainly because direct measurements of spontaneous activity during task performance is challenging, if not impossible. Here for the first time, we used a data-driven approach to obtain the time course of the spontaneous brain activity in two of the well-studied brain networks; 1) the Default mode network (DMN), where the strongest task-evoked negative BOLD response is also observed and 2) the dorsal attention network (DAN), where some of the strongest task-evoked positive BOLD response is observed. Voxel-wise multiple regression analysis is used to model fMRI timeseries with anticipated task-evoked BOLD response, the obtain time course of the spontaneous activity, and their interaction at each participant. Using 46 young and cognitively normal participants performing an event-related perceptual speed task inside the fMRI scanner, we showed that there is no significant interaction between the spontaneous and the task-evoked activity either as negative BOLD response in the DMN or as positive BOLD response in the DAN. We replicate our findings in a separate dataset with 24 young and cognitively normal participants performing a different event-related task inside another fMRI scanner. Our results suggest that the presence or absence of coherent spontaneous activity in the DMN, or DAN has negligible effect on the magnitude of the BOLD response and vice versa, which consequently means that the fMRI signal is a linear superposition of spontaneous and task evoked activity.

Explore related subjects

neurosciencePreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Nayak, S., Hojjati, S. H., Ozoria-Blake, S., Feiz, F., Shteingart, J., Guerrero, A. F., Razlighi, Q. R.. 2023-09-16. Interaction between task-evoked and spontaneous brain activities: Insights from two event-related fMRI studies. https://doi.org/10.1101/2023.09.16.557985

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

The Unreasonable Effectiveness of Cell Types in Describing Neuronal Physiological Features

Single-cell RNA sequencing (scRNA-seq) captures detailed gene expression profiles at scale, while patch-clamp recordings measure intrinsic neuronal electrophysiological properties. Modeling the relations between these two modalities remains a challenge. Here, we compare how well electrophysiological features can be predicted by traditional transcriptomic cell type classification, representations derived from a foundational model (scGPT) pretrained on large-scale scRNA-seq datasets, ion channel-coding genes, and highly variable genes. Using paired transcriptomic and electrophysiological patch-sequencing data from 495 human neurons from neurosurgical tissue, we find that cluster-level cell type representations consistently outperform highly variable gene selection, ion channel gene selection, and context-enriched scGPT embeddings. Notably, performance varies across model architectures and initializations, and the best results are obtained by combining the outputs of separate cell type and scGPT-based models. Together, these findings suggest that traditional discrete cellular classification is highly effective in predicting physiological features. For maximum performance it can be complemented by pretrained transformer models.

neuroscience↗
bioRxiv2026

A nonlinear inhibition pathway underlying cortical responses to tuned holographic optogenetic perturbations

Optogenetics enables causal manipulation of cortical activity. Perturbation responses can be counterintuitive due to network interactions, making theory essential for predicting them. Existing approaches often rely on linear approximations, which fail for many biologically relevant perturbations. Here we develop a nonlinear theory of responses to holographic perturbations in cell-type-specific recurrent networks with structured connectivity. We fit a nonlinear model to mouse V1 data, which shows cotuned-ensemble suppression: perturbing spatially clustered neurons with similar preferred orientations yields markedly stronger short-range suppression than perturbing untuned ensembles. We show that cotuned-ensemble suppression arises from a feature-tuned, nonlinear inhibition pathway implicating somatostatin-positive (SST) interneurons. The theory predicts that cotuned ensembles suppress parvalbumin-positive (PV) neurons but facilitate SST neurons, and links the degree of cotuned-ensemble suppression or facilitation to the variance of the SST response. This framework identifies mechanisms by which nonlinear inhibition sculpts cortical dynamics and establishes a predictive basis for targeted optogenetic interventions.

neuroscience↗
bioRxiv2026

Proteomic signatures of APOE ε4 across human tissues and cell types in Alzheimers disease

The apolipoprotein E {varepsilon}4 (APOE {varepsilon}4) allele is the strongest genetic risk factor for late-onset Alzheimers disease (AD). However, the underlying molecular mechanisms remain unclear. This study included 1691 participants from the Religious Orders Study and Rush Memory and Aging Project (ROSMAP), 1226 participants from the Accelerating Medicines Partnership - Alzheimers Disease (AMP-AD) Diverse Cohorts Study, and 735 participants from the Alzheimers Disease Neuroimaging Initiative (ADNI). To characterise APOE {varepsilon}4 molecular effects, we analysed proteomic data from plasma, cerebrospinal fluid (CSF), and induced pluripotent stem cell (iPSC)-derived astrocytes and neurons, as well as transcriptomic and proteomic data from multiple brain regions. The association of APOE {varepsilon}4 with AD neuropathology was also examined. APOE {varepsilon}4 carriers shared a plasma proteomic signature enriched for immune processes, irrespective of AD diagnosis. A machine learning classifier trained on this signature discriminated APOE {varepsilon}4 carriers from non-carriers in an independent cohort using CSF proteomics. APOE {varepsilon}4 carriage was associated with higher Braak stages and Consortium to Establish a Registry for Alzheimers Disease (CERAD) score. However, only limited APOE {varepsilon}4-associated transcriptomic and proteomic changes were observed in bulk brain tissue, with poor cross-layer concordance. Proteomic analyses of iPSC-derived astrocytes and neurons further revealed cell-type-specific APOE {varepsilon}4-associated changes. APOE {varepsilon}4 is associated with a consistent proteomic signature across plasma and CSF. Its molecular effects in the brain differ across cell types, brain regions and molecular layers. These findings support the need for cell-type-resolved multi-omic studies to elucidate how APOE {varepsilon}4 confers AD risk.

neuroscience↗