Biology subjects

Javidi, S. S.

Publications and source records attributed to Javidi, S. S..

3 recordsLinked to original sources

bioRxiv2026

Structural and Functional Connectivity Predict the Effects of Direct Brain Stimulation on Memory

Intracranial stimulation can enhance episodic memory in humans; however, the behavioral effects vary substantially across individuals and stimulation sites. Here, we investigated whether the network embedding of a stimulation target, defined by MRI-based normative structural and functional connectivity, accounts for variability in stimulation-linked memory enhancement. We analyzed data from 50 adults with medically refractory epilepsy who underwent intracranial EEG monitoring and completed a verbal delayed free-recall task during stimulation of left temporal cortex sites across 61 sessions (39 closed-loop; 22 random). On average, closed-loop stimulation delivered during classifier-detected low-encoding states increased recall rates, whereas random stimulation produced no reliable benefit. Diffusion tractography from a normative database showed that sites yielding greater memory enhancement were characterized by stronger structural coupling to a distributed fronto-temporo-parietal network. Greater structure-function congruence with a normative verbal-encoding activation network predicted larger closed-loop memory benefit (Spearman {rho} = 0.58, P < 0.0001). Functional connectivity exhibited overlapping trends but did not yield robust regional associations after permutation correction. Multivariate Partial Least Squares Structural Equation Modeling further identified stimulation mode, baseline memory, and a structural profile factor as independent predictors of memory enhancement, with no independent contribution of functional connectivity. These findings indicate that reliable stimulation-driven memory improvement depends not only on the timing of stimulation, but also on whether the stimulated target is structurally embedded within an encoding-relevant network scaffold. Significance statementMemory enhancement through direct brain stimulation holds substantial clinical promise, yet inconsistent outcomes have limited its therapeutic translation. This study shows that the effectiveness of closed-loop brain stimulation for memory improvement is determined by the structural network architecture of the stimulation target. Sites more deeply embedded within white-matter pathways connecting a distributed verbal encoding network yield the greatest mnemonic benefits when stimulation is delivered adaptively during poor encoding states. These findings establish a principled, network-based rationale for precision-guided neuromodulation: optimizing both the targets structural embedding and the timing of stimulation delivery are necessary and complementary conditions for reliable, individualized memory enhancement.

neuroscience↗

bioRxiv2026

Mapping Individualized Dual-Axis Network Topology in Focal Epilepsy: Divergent Alterations in System Integrity, Integration, and Clinical Correlates

Focal epilepsy is increasingly recognized as a disorder of distributed brain systems, yet characterizations of patient-specific alterations in network organization that are clinically meaningful remain limited. Here, we used resting-state functional MRI to introduce an overlap-permitting individualized network-estimation framework anchored to normative references to derive two complementary, system-level axes of topology: (1) network correspondence, indexing the expression of canonical networks and the fidelity of intrinsic system boundaries, and (2) k-hubness, indexing cross-system integration and multi-functionality through multi-network participation. We used a large presurgical focal epilepsy cohort (305 patients, including temporal and extratemporal epilepsy; 224 healthy participants) and an independent multi-syndrome validation cohort spanning focal and common generalized and childhood epilepsy syndromes (903 patients; 666 healthy participants), to show: (1) correspondence disruption of both canonical and non-normative networks constitutes a broadly shared system-level endpoint that displays heterogeneity across individuals and differential impacts on cognition, (2) k-hubness reconfigurations reflect lateralized and syndrome-dependent redistributions of cross-system integration, demonstrating epilepsys impact on the functional multiplicity inherent to specific brain areas. These complementary axes shared variance yet showed dissociable clinical associations, with correspondence preferentially relating to neurocognitive deficits and k-hubness aligning with epilepsy clinical features. Accordingly, these axes demonstrate the presence of distinct topological phenotypes, providing clinically relevant, reproducible patient-level signatures that explain both the syndrome-specific and common effects of seizures on the organization and integration of canonical and individualized brain systems.

neuroscience↗

bioRxiv2024

Normative and individual, non-normative intrinsic networks and the transition to impaired cognition

Despite their temporal lobe pathology, a significant subgroup of temporal lobe epilepsy (TLE) patients are able to maintain normative cognitive functioning. Here, we identify TLE patients with intact versus impaired cognitive profiles, and interrogate for the presence of both normative and highly individual intrinsic connectivity networks(ICN) - all towards understanding the transition from impaired to intact neurocognitive status. We retrospectively investigated data from 88 TLE patients and matched 91 healthy controls with resting-state functional MRI. Functional MRI data were decomposed using independent component analysis to obtain individualized ICNs. Here, we calculated the degree of match between individualized ICNs and canonical ICNs (e.g., Yeo et.al 17 resting-state network) and divided each participants ICNs into normative or non-normative status based on the degree of match. We found that the individualized networks matched the canonical networks less well in the cognitively impaired compared to the cognitively intact TLE patients. The cognitively impaired patients showed significant abnormalities in the profiles of both normative and non-normative networks, whereas the intact patients showed abnormalities only in non-normative networks. At the same time, we found normative networks held a strong, positive association with the neuropsychological measures, with this association negative in non-normative networks. We were able to provide the initial data demonstrating that significant cognitive deficits are associated with the status of highly-individual ICNs, making clear that the transition from intact to impaired cognitive status is not simply the result of disruption to normative brain networks.

neuroscience↗