neuroprobe

neuroprobe

Adversarial robustness testing for neural encoding models.

Can a 0.03-norm perturbation to visual features make TRIBE v2 predict auditory cortex activation?
neuroprobe finds out — with gradient-based attacks adapted from adversarial ML for brain-AI interfaces.

Why This Matters

Neural encoding models like Meta's TRIBE v2 — which predict human fMRI brain activity from video, audio, and text — are becoming the foundation of computational neuroscience and BCI safety evaluation. But how robust are these models?

neuroprobe answers this by transplanting adversarial ML techniques from computer vision into neuroscience:

Five Attack Algorithms

neuroprobe
├── BrainFGSM           # Single-step gradient sign (fast baseline)
├── BrainPGD            # Iterative projected gradient descent (strongest)
├── RegionTargeted      # Activate specific ROI, suppress others
├── CrossModalConfusion # Make visual input predict auditory brain activity
└── UniversalBrainPert. # One perturbation that transfers across all stimuli

All attacks operate on the feature space of the encoding model — the (T, D) representation mapped to (T, V) cortical predictions. This is both more tractable (differentiable by construction) and more general than pixel-level attacks.

Quick Start

pip install neuroattack

30-Second Demo (No GPU Required)

import torch
from neuroprobe import BrainPGD, PerturbationBudget, SyntheticEncoder

# Lightweight differentiable brain encoder for testing
model = SyntheticEncoder(feature_dim=768, n_vertices=2048, seed=42)

# Simulate a visual stimulus (10 timesteps, 768-dim features)
stimulus = torch.randn(10, 768)

# PGD attack: find minimal perturbation that maximally shifts brain predictions
budget = PerturbationBudget(epsilon=0.05, norm="linf")
result = BrainPGD(model, budget=budget, n_steps=40).attack(stimulus)

print(f"Brain shift: {result.brain_shift:.4f}")      # Mean |ΔBOLD| across cortex
print(f"L∞ distance: {result.linf_distance:.6f}")     # Perturbation magnitude
print(f"L2 distance: {result.l2_distance:.4f}")
for region, shift in sorted(result.region_shifts.items(), key=lambda x: -x[1])[:5]:
    print(f"  {region:>5s}: {shift:.4f}")

Attack TRIBE v2 (Requires GPU + Model Weights)

import torch
from neuroprobe import BrainPGD, PerturbationBudget
from neuroprobe.wrapper import TRIBEv2Wrapper

# Load the real TRIBE v2 brain encoding model
model = TRIBEv2Wrapper("facebook/tribev2")

# Encode a video stimulus
features = model.encode_stimulus("path/to/video.mp4")

# Run adversarial attack
budget = PerturbationBudget(epsilon=0.03, norm="linf")
result = BrainPGD(model, budget=budget, n_steps=50).attack(features)

print(f"Brain shift: {result.brain_shift:.4f}")
print(f"Most affected region: {max(result.region_shifts, key=result.region_shifts.get)}")

Region-Targeted Attack

Can we craft a perturbation that selectively activates the fusiform face area (FFA) while leaving auditory cortex untouched?

from neuroprobe import RegionTargeted

attacker = RegionTargeted(
    model,
    target_region="FFA",                         # Activate face processing area
    suppress_regions=["A1", "STG", "STS"],        # Keep auditory regions stable
    n_steps=100,
    target_activation=2.0,                        # Push FFA to 2.0 BOLD units
)
result = attacker.attack(stimulus)
print(f"FFA shift: {result.region_shifts.get('FFA', 0):.4f}")
print(f"A1 shift:  {result.region_shifts.get('A1', 0):.4f}")   # Should be ~0

Cross-Modal Confusion

Perturb visual features so the model predicts brain activity typical of auditory processing:

from neuroprobe import CrossModalConfusion

attacker = CrossModalConfusion(model, source_modality="visual", n_steps=80)
result = attacker.attack(visual_features)
# Result: model now predicts auditory cortex activation from visual input

Universal Adversarial Perturbation

Learn a single perturbation that transfers across all stimuli:

from neuroprobe import UniversalBrainPerturbation

uap = UniversalBrainPerturbation(model, n_epochs=10)
delta = uap.fit(training_stimuli)  # Learn from multiple stimuli
result = uap.attack(new_stimulus)  # Apply to unseen stimulus
print(f"Universal perturbation transfers with brain_shift={result.brain_shift:.4f}")

Full Robustness Audit

Run a complete robustness evaluation with a single function:

from neuroprobe import robustness_curve, region_vulnerability_map

# Robustness curve: brain shift vs. perturbation budget
reports = robustness_curve(model, stimuli, epsilons=[0.001, 0.005, 0.01, 0.05, 0.1])
for eps, report in reports.items():
    print(f"ε={eps:.3f}  shift={report.mean_brain_shift:.4f}  "
          f"most_vulnerable={report.most_vulnerable_region}")

# Which brain regions are most vulnerable to targeted attacks?
vuln = region_vulnerability_map(model, stimuli, n_steps=50)
for region, score in vuln.items():
    print(f"  {region:>5s}: {'█' * int(score * 20):<20s} {score:.4f}")

CLI

# Quick demo with SyntheticEncoder
neuroprobe demo --attack pgd --steps 40 --epsilon 0.05

# Full audit with JSON output
neuroprobe audit --epsilon 0.01,0.05,0.1 --output report.json

Architecture

Stimulus ──► Encoder ──► Features (T, D) ──► Brain Model ──► BOLD (T, V)
                              │                                    │
                         neuroprobe                          ◄─ gradients
                         perturbs here                         flow back

neuroprobe attacks the feature representation between the stimulus encoder and the brain prediction head. This is the critical interface where:

• Gradient access is guaranteed (differentiable by construction)
• Perturbations are semantically meaningful (feature space, not pixel space)
• Results generalize across input modalities (video, audio, text share this interface)

The BrainEncoderWrapper ABC lets you plug in any model:

from neuroprobe.wrapper import BrainEncoderWrapper

class MyModel(BrainEncoderWrapper):
    def encode_stimulus(self, stimulus):
        return my_encoder(stimulus)  # → (T, D)

    def predict_from_features(self, features):
        return my_brain_head(features)  # → (T, V), must be differentiable

Cortical ROI Definitions

13 standard regions on the fsaverage5 cortical mesh (20,484 vertices), covering:

Testing

pip install neuroattack[dev]
pytest tests/ -v    # 64 tests, ~60s

Citation

If you use neuroprobe in your research:

@software{neuroprobe2025,
  title={neuroprobe: Adversarial Robustness Testing for Neural Encoding Models},
  author={Zacharie B},
  year={2025},
  url={https://github.com/stef41/neuroprobe}
}

Related Work

• TRIBE v2 — Meta's brain encoding foundation model (d'Ascoli et al., 2026)
• Adversarial Examples for Neural Encoding Models — Adversarial vulnerability of visual encoding models
• Brain-Score — Benchmarking neural encoding models
• Universal Adversarial Perturbations — Moosavi-Dezfooli et al., 2017

License

Apache 2.0