core-cross-site-ood-brain-network

name: core-cross-site-ood-brain-network description: > CORE (Cross-site OOD Robust brain nEtwork) framework for brain network learning across unseen sites. Addresses cross-site out-of-distribution degradation in fMRI graph-based learning through site-aware confounder decoupling, transient pathway dynamics profiling, line graph organization for transferable pathway-level modeling, and prior-guided subject-adaptive gating. Use when working with cross-site fMRI brain network analysis, OOD generalization in neuroimaging, site-conditioned bias mitigation, transient neurodynamics modeling, or multi-site brain disorder classification. Triggers: cross-site OOD, brain network generalization, site bias, confounder decoupling, CORE framework, transient pathway, line graph brain, multi-site fMRI.

CORE: Cross-site OOD Robust brain nEtwork

Unified framework for brain network learning across unseen sites. Addresses two key failures in existing methods: (1) site-conditioned confounders induce non-pathological shortcuts, and (2) temporal averaging obscures transient neurodynamics, limiting generalization.

Problem Statement

Graph-based learning on fMRI shows strong potential but degrades under cross-site OOD settings because:

1. Site-conditioned confounders create non-pathological shortcuts
2. Temporal averaging in FC construction obscures transient neurodynamics

Three-Stage Architecture

Stage 1: Site-Aware Confounder Decoupling

Extracts cross-site population scaffold of reproducible diagnostic connectivity edges by mitigating site-conditioned bias.

Raw FC → Site confounder removal → Scaffold edges (diagnostic, reproducible)

Key insight: Separate site-specific variation from population-level disease signal.

Stage 2: Transient Pathway Dynamics Profiling

Profiles transient dynamics over the scaffold using lightweight temporal descriptors and organizes scaffold edges into a line graph for transferable pathway-level modeling.

Scaffold edges → Line graph → Pathway dynamics → Transferable representations

Line Graph Construction: Each edge in the original brain network becomes a node in the line graph, enabling pathway-level (edge-to-edge) analysis.

Stage 3: Prior-Guided Subject-Adaptive Gating

Leverages scaffold-derived population priors while preserving subject-specific connectivity variability through an adaptive gating mechanism.

Population prior ⊗ Subject-specific gating → Final representation

Implementation Pattern

import torch
import torch.nn as nn

class CORE(nn.Module):
    def __init__(self, n_regions, n_sites, scaffold_edge_dim, pathway_dim):
        super().__init__()
        # Stage 1: Confounder decoupling
        self.site_encoder = nn.Embedding(n_sites, 64)
        self.decoupler = nn.Sequential(
            nn.Linear(n_regions * n_regions, 256),
            nn.ReLU(),
            nn.Linear(256, scaffold_edge_dim)
        )

        # Stage 2: Line graph + pathway dynamics
        self.line_graph_conv = nn.Sequential(
            nn.Linear(scaffold_edge_dim, pathway_dim),
            nn.ReLU(),
            nn.Linear(pathway_dim, pathway_dim)
        )
        self.temporal_descriptor = nn.GRU(
            input_size=pathway_dim,
            hidden_size=pathway_dim,
            batch_first=True
        )

        # Stage 3: Subject-adaptive gating
        self.gate = nn.Sequential(
            nn.Linear(scaffold_edge_dim, 64),
            nn.ReLU(),
            nn.Linear(64, scaffold_edge_dim),
            nn.Sigmoid()
        )

        self.classifier = nn.Linear(pathway_dim, 2)

    def forward(self, fc_matrix, site_id, time_series=None):
        # Stage 1: Decouple site confounders
        site_embed = self.site_encoder(site_id)
        scaffold = self.decoupler(fc_matrix.view(fc_matrix.size(0), -1))

        # Stage 2: Line graph + temporal dynamics
        pathway = self.line_graph_conv(scaffold)
        if time_series is not None:
            temporal_out, _ = self.temporal_descriptor(pathway.unsqueeze(1))
            pathway = temporal_out[:, -1]

        # Stage 3: Adaptive gating
        gate_weights = self.gate(scaffold)
        representation = pathway * gate_weights

        return self.classifier(representation), scaffold, gate_weights

Line Graph for Brain Networks

Transform edge-level brain connectivity to pathway-level representations:

def build_line_graph(adjacency):
    """Convert brain network adjacency to line graph.

    Each edge (i,j) in original graph becomes a node in line graph.
    Two line-graph nodes are connected if their corresponding edges
    share a vertex in the original graph.
    """
    n = adjacency.shape[0]
    edges = []
    for i in range(n):
        for j in range(i+1, n):
            if adjacency[i, j] > 0:
                edges.append((i, j))

    n_edges = len(edges)
    line_adj = torch.zeros(n_edges, n_edges)
    for a in range(n_edges):
        for b in range(a+1, n_edges):
            # Share a vertex?
            if (edges[a][0] == edges[b][0] or
                edges[a][0] == edges[b][1] or
                edges[a][1] == edges[b][0] or
                edges[a][1] == edges[b][1]):
                line_adj[a, b] = line_adj[b, a] = 1
    return line_adj

Key Datasets

• ABIDE: Autism Brain Imaging Data Exchange
• REST-meta-MDD: Resting-state MDD dataset
• SRPBS: Suzuki Resting-State fMRI Database
• ABCD: Adolescent Brain Cognitive Development

Evaluation Protocol

Leave-one-site-out evaluation: Train on N-1 sites, test on held-out site.

Results show up to 6.7% relative gain over baselines, robust to atlas variations across different brain parcellation schemes.

Advantages Over Baselines

Workflow

1. Collect multi-site fMRI data: Gather FC matrices + temporal series
2. Build scaffold: Apply confounder decoupling to extract reproducible edges
3. Construct line graph: Transform edge-level to pathway-level representation
4. Profile transient dynamics: Use temporal descriptors over time windows
5. Apply adaptive gating: Combine population prior with subject variability
6. Evaluate cross-site: Leave-one-site-out protocol

Activation Keywords

• cross-site brain network
• OOD neuroimaging
• site confounder decoupling
• transient pathway dynamics
• line graph brain network
• multi-site fMRI generalization
• CORE framework
• subject-adaptive gating
• brain network transfer learning