Biology subjects

ASANO, E.

Publications and source records attributed to ASANO, E..

7 recordsLinked to original sources

bioRxiv2025

Whole-Brain Millisecond-Scale Effective Connectivity Atlas of Auditory and Visual Naming

Neurobiological models suggest that speech relies on interactions among distant cortical regions interconnected by white matter pathways. Prior studies have shown that speech-related functional coactivation--simultaneous high-gamma augmentation across distributed regions--reflects underlying neural interactions, as validated by electrical stimulation mapping. However, it remains unclear at the whole-brain level when, for how long, and in which directions cortical regions transmit information, and how dynamic information flows contribute to speech. Here, we investigated the causal roles of directional neural information flow during auditory and visual naming using intracranial EEG from 9,526 artifact-free nonepileptic sites across 127 patients. Information flow, estimated by transfer entropy-based effective connectivity, was classified as excitatory when high-gamma acceleration in one region predicted subsequent acceleration in another, and inhibitory when deceleration predicted downstream deceleration. Following stimulus onset, excitatory flows emerged from modality-specific sensory cortices and propagated to higher-order regions, later becoming bidirectional as functional coactivation developed. Each excitatory flow event was transient (<500 ms), typically followed by inhibitory flows and decreased coactivation, during which excitatory flows often emerged along new pathways. During auditory naming, faster response times were associated with stronger excitatory flows in left perisylvian regions; during visual naming, faster responses were linked to stronger flows in bilateral basal temporal cortices. Stronger excitatory flows at specific time points predicted a higher probability of stimulation-induced symptoms (Spearmans rho: 0.54-0.81; p<0.00001), whereas associations with inhibitory flows peaked later. Excitatory flows near visual naming response onset were particularly associated with stimulation-induced speech arrest and face sensorimotor symptoms, whereas functional coactivation alone failed to reveal comparable associations. These findings demonstrate that transient acceleration of directional neural interactions through white matter supports successive stages of speech processing. As activity within one pathway decelerates, excitatory flow accelerates along another, enabling functional transitions critical for naming. By establishing the causal contribution of temporally precise, anatomically specific white matter pathways, this study substantiates and extends existing neurobiological models of speech. To facilitate replication and dynamic whole-brain visualization, we provide open access to the full dataset (62.15 GB) and analysis code.

neuroscience↗

bioRxiv2025

Dynamic Causal White Matter Atlas of Auditory and Visual Speech Networks at Millisecond Resolution: Intracranial Evidence from 125 Patients

Background and ObjectivesSince the era of Penfield, invasive neurophysiology has laid a lasting foundation for functional neuroscience by elucidating brain regions necessary for speech. However, whole-brain investigations have yet to distinguish the millisecond-scale dynamics and specific white matter pathways that support rapid naming in the auditory and visual domains. MethodsIn this observational study, we constructed a whole-brain Dynamic Causal Tractography atlas using intracranial neurophysiological data from 125 neurosurgical patients. The resulting video atlas captured local cortical high-gamma activity and cortico-cortical coactivation via white matter tracts during rapid and delayed auditory and picture naming. Direct electrical stimulation was employed to assess the causal significance of the observed neural dynamics. ResultsThe atlas revealed white matter coactivation intensity patterns at specific 5-millisecond time windows that best aligned with sensorimotor and language symptoms elicited by electrical stimulation (Spearmans {rho} = 0.58-0.91; p = 4.8 x 10cc to 1.6 x 10c{superscript 2}c). Rapid auditory naming was associated with deactivation of the right rostral middle frontal gyrus and increased coactivation along the left arcuate fasciculus, linked to stimulation-induced receptive and expressive aphasia. In contrast, delayed auditory naming correlated with a late surge in bifrontal coactivation. Rapid picture naming involved early coactivation between cortices connected via the bilateral inferior longitudinal fasciculi--associated with stimulation-induced visual distortions--coinciding with transient co-inactivation of Brocas area. DiscussionThese findings delineate dissociable white matter-mediated mechanisms supporting rapid naming in the auditory and visual domains. Reduced inhibitory monitoring by the right dorsolateral prefrontal cortex may facilitate efficient lexical retrieval via left perisylvian pathways during auditory naming. In contrast, excessive bifrontal interaction may underlie delayed auditory naming. Rapid visual object recognition appears to rely on early occipitotemporal coactivation with minimal involvement of Brocas area. The resulting atlas--accompanied by a publicly available dataset (61.2 GB) and analysis code--serves as a valuable resource for students and trainees studying the network dynamics underlying speech, as well as for presurgical language mapping in patients undergoing cortical or subcortical intervention.

neuroscience↗

bioRxiv2025

Millisecond-Scale White Matter Dynamics Underlying Visuomotor Integration

In the conventional neuropsychological model, nonverbal visuospatial processing is predominantly handled by the right hemisphere, whereas verbal processing occurs in the left, with right-hand responses governed by the left motor cortex. Using intracranial EEG and MRI tractography, we investigated the timing and white matter networks involved in processing nonverbal visuospatial stimuli, forming response decisions, and generating motor outputs. Within 200 ms of stimulus onset, we observed widespread increases in functional connectivity and bidirectional neural flows from visual to association cortices, predominantly in the right hemisphere. Engagement of the right anterior middle frontal gyrus improved response accuracy; however, the accompanying enhancement in intra-hemispheric connectivity delayed response times. In the final 100 ms before right-hand response, functional connectivity and bidirectional communication via the corpus callosum between the right and left motor cortices became prominent. These findings provide millisecond-level support for the established model of hemispheric specialization, while highlighting a trade-off between accuracy and speed governed by the right dorsolateral prefrontal network. They also underscore the critical timing of callosal transmission of response decisions formed in right-hemispheric networks to the left-hemispheric motor system. HighlightsNeural information propagates through fasciculi during a visuomotor task. Non-verbal visuospatial analysis is mediated with right-hemispheric dominance. The right middle frontal gyrus improves response accuracy but delays responses. Interhemispheric information transfer occurs immediately before motor responses. This transfer between motor cortices is mediated by the corpus callosum.

neuroscience↗

bioRxiv2025

Normative high-frequency oscillation phase-amplitude coupling and effective connectivity under sevoflurane

Resective surgery for pediatric drug-resistant focal epilepsy often requires extraoperative intracranial electroencephalography recording to accurately localize the epileptogenic zone. This procedure entails multiple neurosurgeries, intracranial electrode implantation and explantation, and days of invasive inpatient evaluation. There is a need for methods to reduce diagnostic burden and introduce objective epilepsy biomarkers. Our preliminary studies aimed to address these issues by using sevoflurane anesthesia to rapidly and reversibly activate intraoperative phase-amplitude coupling between delta and high-frequency activities, as well as high-frequency activity-based effective connectivity. Phase-amplitude coupling can serve as a proxy for spike-and-wave discharges, and effective connectivity describes the spatiotemporal dynamics of neural information flow among regions. Notably, sevoflurane activated these interictal electrocorticography biomarkers most robustly in areas whose resection led to seizure freedom. However, they were also increased in normative brain regions that did not require removal for seizure control. Before using these electrocorticography biomarkers prospectively to guide resection, we should understand their endogenous distribution and propagation pathways, at different anesthetic stages. In the current study, we highlighted the normative distribution of delta and high-frequency activity phase-amplitude coupling and effective connectivity under sevoflurane. Normative data was derived from nineteen patients, whose ages ranged from four to eighteen years and included eleven males. All achieved seizure control following focal resection. Electrocorticography was recorded at an isoflurane baseline, during stepwise increases in sevoflurane concentration, and also during extraoperative slow-wave sleep without anesthesia. Normative electrode sites were then mapped onto a standard cortical surface for anatomical visualization. Dynamic tractography traced white matter pathways that connected sites with significantly augmented biomarkers. Finally, we analyzed all sites --regardless of normal or abnormal status -- to determine whether sevoflurane-enhanced biomarker values could intraoperatively localize the epileptogenic sites. We found that normative electrocorticography biomarkers increased as a function of sevoflurane concentration, especially in bilateral frontal and parietal lobe regions (Bonferroni-corrected p-values <0.05). Callosal fibers directly connected homotopic Rolandic regions exhibiting elevated phase-amplitude coupling. The superior longitudinal fasciculus linked frontal and parietal association cortices showing augmented effective connectivity. Higher biomarker values, particularly at three to four volume percent sevoflurane, characterized epileptogenicity and seizure-onset zone status (Bonferroni-corrected p-values <0.05). Supplementary analysis showed that epileptogenic sites exhibited less augmentation in delta-based effective connectivity. This study helps clarify the normative distribution of, and plausible propagation pathways supporting, sevoflurane enhanced electrocorticographic biomarkers. Future work should confirm that sevoflurane-activated electrocorticography biomarkers can predict postoperative seizure outcomes in larger cohorts, to establish their clinical utility.

neuroscience↗

bioRxiv2025

Visualization of functional and effective connectivity underlying auditory descriptive naming

ObjectiveWe visualized functional and effective connectivity within specific white matter networks in response to auditory descriptive questions. MethodsWe investigated 40 Japanese-speaking patients with focal epilepsy and estimated connectivity measures using cortical high-gamma dynamics and MRI tractography. ResultsHearing a wh-interrogative at question onset enhanced inter-hemispheric functional connectivity, with left-to-right callosal facilitatory flows between the superior-temporal gyri, contrasted by functional connectivity diminution with right-to-left callosal suppressive flows between dorsolateral prefrontal regions. Processing verbs associated with concrete objects or adverbs increased left intra-hemispheric connectivity, with bidirectional facilitatory flows through extensive white matter pathways. Questions beginning with what, compared to where, induced greater neural engagement in the left posterior inferior-frontal gyrus at question offset, linked to enhanced functional connectivity and bidirectional facilitatory flows to the temporal lobe neocortex via the arcuate fasciculus. During overt responses, inter-hemispheric functional connectivity was enhanced, with bidirectional callosal flows between Rolandic areas, and individuals with higher IQ scores exhibited less prolonged neural engagement in the left posterior middle frontal gyrus. ConclusionsVisualization of directional neural interactions within white matter networks during overt naming is feasible. SignificancePhrase order may influence network dynamics in listeners, even when presented with auditory descriptive questions conveying similar meanings.

neuroscience↗

bioRxiv2022

Dynamic cortical and tractography atlases of proactive and reactive alpha and high-gamma activities

Alpha waves - posterior-dominant rhythms at 8-12 Hz reactive to eye opening and closure - are among the most fundamental EEG findings in clinical practice and research since Hans Berger first documented them in the early 20th century. Yet, the exact network dynamics of alpha waves in regard to eye movements remains unknown. High-gamma activity at 70-110 Hz is also reactive to eye movements and a summary measure of local cortical activation supporting sensorimotor or cognitive function. We aimed to build the first-ever brain atlases directly visualizing the network dynamics of eye movement-related alpha and high-gamma modulations, at cortical and white matter levels. We studied 28 patients (age: 5-20 years) who underwent intracranial EEG and electrooculography recordings. We measured alpha and high-gamma modulations at 2,170 electrode sites outside the seizure onset zone, interictal spike-generating areas, and MRI-visible structural lesions. Dynamic tractography animated white matter streamlines modulated significantly and simultaneously beyond chance, on a millisecond scale. Before eye closure onset, significant alpha augmentation occurred at the occipital and frontal cortices. After eye closure onset, alpha-based functional connectivity was strengthened, while high gamma-based connectivity was weakened extensively in both intrahemispheric and interhemispheric pathways involving the central visual areas. The inferior fronto-occipital fasciculus supported the strengthened alpha coaugmentation-based functional connectivity between occipital and frontal lobe regions, whereas the posterior corpus callosum supported the interhemispheric functional connectivity between the occipital lobes. After eye opening offset, significant high gamma augmentation and alpha attenuation occurred at occipital, fusiform, and inferior parietal cortices. High gamma coaugmentation-based functional connectivity was strengthened, whereas alpha-based connectivity was weakened in the posterior interhemispheric and intrahemispheric white matter pathways involving central and peripheral visual areas. Proactive and reactive alpha waves involve extensive, distinct white matter networks that include the frontal lobe cortices, along with low- and high-order visual areas. High-gamma co-attenuation coupled to alpha co-augmentation in shared brain circuitry after eye closure supports the notion of an idling role for alpha waves during eye closure. These dynamic tractography atlases may improve understanding of the significance of EEG alpha waves in assessing the functional integrity of brain networks in clinical practice; they also may help elucidate the effects of eye movements on task-related brain network measures observed in cognitive neuroscience research.

neuroscience↗

bioRxiv2021

Refining epileptogenic high-frequency oscillations using deep learning: a reverse engineering approach

Intracranially-recorded interictal high-frequency oscillations (HFOs) have been proposed as a promising spatial biomarker of the epileptogenic zone. However, visual verification of HFOs is time-consuming and exhibits poor inter-rater reliability. Furthermore, no method is currently available to distinguish HFOs generated from the epileptogenic zone (epileptogenic HFOs: eHFOs) from those generated from other areas (non-epileptogenic HFOs: non-eHFOs). To address these issues, we constructed a deep learning (DL)-based algorithm using HFO events from chronic intracranial electroencephalogram (iEEG) data via subdural grids from 19 children with medication-resistant neocortical epilepsy to: 1) replicate human expert annotation of artifacts and HFOs with or without spikes, and 2) discover eHFOs by designing a novel weakly supervised model (HFOs from the resected brain regions are initially labeled as eHFOs, and those from the preserved brain regions as non-eHFOs). The "purification power" of DL is then used to automatically relabel the HFOs to distill eHFOs. Using 12,958 annotated HFO events from 19 patients, the model achieved 96.3% accuracy on artifact detection (F1 score = 96.8%) and 86.5% accuracy on classifying HFOs with or without spikes (F1 score = 80.8%) using patient-wise cross-validation. Based on the DL-based algorithm trained from 84,602 HFO events from nine patients who achieved seizure-freedom after resection, the majority of such DL-discovered eHFOs were found to be HFOs with spikes (78.6%, p < 0.001). While the resection ratio of detected HFOs (number of resected HFOs/number of detected HFOs) did not correlate significantly with post-operative seizure freedom (the area under the curve [AUC]=0.76, p=0.06), the resection ratio of eHFOs positively correlated with post-operative seizure freedom (AUC=0.87, p=0.01). We discovered that the eHFOs had a higher signal intensity associated with ripple (80-250 Hz) and fast ripple (250-500 Hz) bands at the HFO onset and with a lower frequency band throughout the event time window (the inverted T-shaped), compared to non-eHFOs. We then designed perturbations on the input of the trained model for non-eHFOs to determine the models decision-making logic. The model probability significantly increased towards eHFOs by the artificial introduction of signals in the inverted T-shaped frequency bands (mean probability increase: 0.285, p < 0.001), and by the artificial insertion of spike-like signals into the time domain (mean probability increase: 0.452, p < 0.001). With this DL-based framework, we reliably replicated HFO classification tasks by human experts. Using a reverse engineering technique, we distinguished eHFOs from others and identified salient features of eHFOs that aligned with current knowledge. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/458385v1_ufig1.gif" ALT="Figure 1"> View larger version (81K): org.highwire.dtl.DTLVardef@39977dorg.highwire.dtl.DTLVardef@108b182org.highwire.dtl.DTLVardef@1bdf864org.highwire.dtl.DTLVardef@fe9e57_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗