Biology subjects

Yanez-Ramos, M. G.

Publications and source records attributed to Yanez-Ramos, M. G..

4 recordsLinked to original sources

bioRxiv2026

White matter conduction in the human brain is mostly slow, with rare high velocity connections

White matter bundles play a crucial role in cognitive functions by rapidly transmitting information between brain regions. Inter-areal conduction guides the integration of information and conduction velocity is a fundamental parameter in theories and models of brain function. However, distributions of conduction velocity remain difficult to characterize in vivo in humans. In this work, we integrated diffusion magnetic resonance imaging (dMRI) tractography with intracranial electrical stimulation during clinical stereo-electroencephalography (sEEG) monitoring in 17 subjects to measure conduction velocity within four major white matter bundles. Our findings reveal that human brain conduction is characterized by high variability both within and between bundles, reflecting a predominance of slow connections alongside rare high-speed connections. Because conduction velocity in myelinated fibers follows an approximately linear relationship with axon diameter, we derive underlying axon diameter distributions and show that these estimates are comparable to previous post-mortem studies. These findings demonstrate a heavily skewed distribution of human neural conduction velocities and show that structural heterogeneity shapes the timing and integration of information in large-scale networks.

neuroscience↗

bioRxiv2026

Graded Centro-Parietal Responses During Contextual Integration Across Symbolic Domains

Many cognitive processes depend on integrating information as it becomes available to construct meaningful interpretations. Prior work has shown graded and incremental context effects, especially in language, but it remains less clear whether contextual integration exhibits a comparable temporal profile across symbolic domains when structured input is examined within congruent sequences. Twenty-seven participants processed congruent four-element sequences designed to be structurally comparable across lexical, algebraic, and graphical domains while event-related potentials were recorded. In the 250-500 ms interval, mean amplitudes increased systematically with sequence position within a predefined centro-parietal region of interest (p < .001). The Domain x Position interaction did not reach significance (p = .056), although modest domain-related differences in the buildup profile cannot be ruled out. A follow-up analysis showed that the increase to the response-relevant final position was larger than earlier increases (p < .001). Additional analyses indicated maximal amplitudes over parietal sites and the clearest graded increase over central sites. These findings indicate that context-sensitive activity was progressive but not uniform across sequence positions, with the strongest increase occurring when the sequence reached its final, response-relevant completion point. The presence of position-related increases across lexical, algebraic, and graphical domains is consistent with the view that centro-parietal ERP activity in the 250-500 ms window tracks the progressive buildup of contextual integration during structured sequence processing. HighlightsO_LIContext-sensitive ERP activity increased across sequence position. C_LIO_LIThe strongest increase occurred at the final completion point. C_LIO_LIMaximal amplitudes were observed over parietal electrodes. C_LIO_LICentral sites best captured graded position-related modulation. C_LIO_LIPosition-related buildup was observed across symbolic domains. C_LI

neuroscience↗

bioRxiv2026

A Systematic Characterization of Causal Interactions Between Human Visual Areas

Human visual cortex comprises three interacting streams, but anatomy and correlated activity cannot determine the direction or reliability of interareal influence. Characterizing directional interactions among these streams can reveal the architecture through which activity can propagate across the visual system. Here, we used single-pulse electrical stimulation during intracranial EEG recordings in 23 patients to map directed effective connectivity among 22 atlas-defined visual cortical areas. The resulting effective connectivity matrix revealed a selective and asymmetric architecture of interareal influence. Feedforward influences from early visual areas to the dorsal and lateral streams were more reliable and more prevalent than the corresponding feedback influences, whereas interactions between early visual and ventral temporal areas were comparatively balanced. Cross-stream interactions favored temporal-to-parietal over parietal-to-temporal influence, with higher response reliability and a greater proportion of significant responses among sampled connections. Network-level profiles were consistent with source-like organization in early visual areas and the ventral stream, and integrator-like organization in the dorsal and lateral streams. Visual-task data collected in three of the same patients illustrated how stimulation-derived connectivity may relate to functional responses across connected visual regions. These findings reveal a directional architecture for activity propagation across the human visual cortex and provide empirical constraints for biologically grounded models of visual processing.

neuroscience↗

bioRxiv2025

Human pulvinar stimulation engages select cortical pathways in epilepsy

The pulvinar has been proposed as an effective neuromodulation target for patients with posterior quadrant and temporal epilepsies. However, the pulvinar has a large tissue volume, multiple subnuclei, and widespread cortical connections. It remains unknown whether electrical stimulation of distinct pulvinar subregions affects the temporal, occipital, and parietal areas differently. To address this gap, we delivered single-pulse electrical stimulation to the pulvinar and measured the resulting brain stimulation evoked potentials in twelve patients undergoing stereotactic EEG for drug-resistant epilepsy. Brain stimulation evoked potentials were parameterized across the occipital, temporal and parietal cortex. Stimulation of the lateral pulvinar elicited significant brain stimulation evoked potentials in striate and extrastriate areas that diminish as stimulation shifts towards the medial pulvinar. Conversely, stimulation of the ventral aspect of the medial pulvinar produced significant lateral temporal evoked potentials, which diminish with lateral pulvinar stimulation. We also found that stimulation of the dorsomedial pulvinar evoked significant parietal responses with limited striate/extrastriate and lateral temporal responses. These results demonstrate that electrical stimulation of specific pulvinar subregions influences distinct occipital, parietal and lateral temporal areas. Selective targeting of pulvinar subregions to maximize seizure network engagement may be essential for individualized treatment of posterior quadrant and temporal epilepsies.

neuroscience↗