International Society for Tractography 2025

Day 1 - Monday, October 13 2025 – Opening session

Speaker 1: Maxime Descoteaux - Introduction to the IST

• Handbook of Diffusion MR Tractography took 10 years to write from inception
• IST officially created in 2023
• Millenium pathways for tractography paper - Came from the roundtables in TractAnat retreat in 2024
• IST 2026 in Banff in Oct. 2026, IST Winter School in Verona in Feb. 2026
• GA Thursday Oct. 16th 2025, scientific unit discussions

Speaker 2: Denis Le Bihan - Diffusion MRI and Einstein’s legacy – The emergence of consciousness from the brain connectome –

• Measuring diffusion of water molecules in the brain to see at the macro (mm) scale
• Stejskal EO et al., 1965 — “Spin Diffusion Measurements: Spin Echoes in the Presence of a Time-Dependent Field Gradient.”
• The b-value formalism links gradient strength, timing, and diffusion time to signal attenuation.
• Le Bihan D et al., 1986 — “MR imaging of intravoxel incoherent motions: application to diffusion and perfusion in neurologic disorders.”
• Moseley ME et al., 1990 — “Early detection of regional cerebral ischemia in cats: comparison of diffusion- and T2-weighted MRI and spectroscopy.”
• Moseley ME et al., 1990 — “Diffusion-weighted MR imaging of anisotropic water diffusion in cat brain and spine.”
• Douek P et al., 1991 — “MR color mapping of myelin fiber orientation.”
• Basser PJ et al., 1994 — “MR diffusion tensor spectroscopy and imaging.”
• Mori S et al., 1999 — “Three-dimensional tracking of axonal projections in the brain by magnetic resonance imaging.”
• Gray matter organized in regions, white matter has been overlooked
• White matter grows faster than gray matter in development and size
• Gray matter is “spatial segregation”, white matter is “temporal integration”
• “Consciousness explained by Einstein’s work ?”
• Action potential has a speed limit
• “Relativity and diffusion are not compatible”
• Different brain regions activate at same time but can’t know about each other at same time
• Brain regions are connected by time instead of space
• “You believe you decide if you see a face or a vase but it’s not true”
• Brain connectome is a 4D Minkowski spacetime
• Psychiatry: “clock asynchrony” results in inner voices perceived as external voices
• Feeling of slowness or heaviness in depression might be associated with physical slowdown
• Denis Le Bihan book: Einstein’s Error at the frontier of the brain and the cosmos
• Social magnet from DTI & fMRI
• Restoring consciousness by restoring spacetime curvature in the brain
• Holographic principle : reality is a 3D projection of reality encoded on a 2D surface
• Consciousness = Geometry : 5D spacetime curvature (~ gravity)
• 5D connectome spacetime allows the immaterial emergence of consciousness as a dual to the material brain

Denis Le Bihan cuts the ribbon to inaugurate the IST 2025 conference.

Day 1 - Monday, October 13 2025 – Oral session 1

Saad Jbabdi - SPOT: Spatial Pointwise Orientation Tracking ( Tractography: have we been doing it wrong all along? )

• “We are obsessed with FOD”
• Two different structures can give the same FOD
• FOD can “hallucinate”
• Main idea is to find a model that bypasses FOD
• Pointwise vector field, model from x,y,z to F
• Is actually an INR, implicit neural representation
• Can include multiple modalities like PLI (polarized light imaging) and DMRI
• Using fourier features
• Give the MLP a spatial coordinate and get the PLI and dMRI signal
• Trained using … (loss, etc)
• Scale 0.0001, 0.001, 0.01, 0.1??
• Real data: x,y,z -> diffusion + ADC + S0
• Super resolution means no crossing fibers because in reality fibers don’t cross, they interdigitate

Ruben Vink - Estimating Brain Fibers via Volumetric Cortical Folding Deformation

• Tractography has limitations
• Incorporating anatomical priors into tractography
• Monkey brain, PLI shows structures far smaller than typical dMRI resolution
• Want to capture folding in cortical areas
• “can mapping the cortical fold development help tractography”?
• Tangential expansion of cortical surface during development
• Folding is hard, reverse folding is much simpler
• Tracking -> unfolding -> radial fibers -> refolding
• Doesn’t actually need diffusion data for folding -> radial fibers -> refolding
• Limitations: slow (1h total), simulation model (not capturing all relevant structures)

Alfred Anwander - Local Spherical Deconvolution (LSD) for Tractography of High-Resolution Diffusion MRI of Chimpanzee Brains

• Cannot do invasive studies on great apes
• Can we get anatomical information from great apes post-mortem?
• Benefits: longer acquisition time, higher resolution, no motion
• Challenges: fixatives
• Description of their fancy scanner
• 4 days scan, 500um resolution, publicly available
• Using local spherical deconvolution (LSD) instead of Constrained Spherical Deconvolution (CSD)
• Cleaner FODs with sharper peaks, because of spatially varying deconvolution kernel and account for microstructural differences
• They can track the “precursor” of the language pathway in chimpanzees
• 100 great apes scanned, data will be publicly available

Charles Poirier - Towards Whole-Brain Tractography of the Mouse from Serial Optical Coherence Tomography

• OCT is a label-free imaging technique, no tissue or tracer injection
• Polarization sensitive OCT (PS-OCT) can measure fiber orientation, but complex setup
• 3.5 x 3.5 x 3 um resolution
• Acquired in tiles, 200 um slab thickness
• In place resolution is good, tile blending is seamless
• Out of place reconstruction is hard
• In or out of place bundles can be tracked, but crossing fibers are hard to resolve

Day 1 - Monday, October 13 2025 – Afternoon

Lauren O’Donnell / Jarrett Rushmore - What is a bundle definition?

• Everyone disagrees on the “definition of a bundle definitions”
• Paper coming
• Definitions of “bundle definition” are very different
• Started on internal capsule
• Computer scientist suggested to text files defining pathways and summarize with ChatGPT
• Neuroanatomists suggest start with internal capsule and consider directionality, …
• Our goal is to provide a definition
• Neuroanat focus on history, nomenclature, axons indiv.
• Computer scientists focus on org. formatting info
• Clinicians focus on using tracto to guide surgery
• Competing terminologies are common but neuroanatomy is particularly bad
• Zilles K et al., 2010 — “Centenary of Brodmann’s map—conception and fate.”
• Why the internal capsule?
• Studied for 200 years, earliest description
• ten Donkelaar HJ et al., 2018 — “An Illustrated Terminologia Neuroanatomica: A Concise Encyclopedia of Human Neuroanatomy.”
• Next paper topic: Top clinical bundles

Roundtable wrap-up:

• What do you want from a bundle def
  • multi-scale and context dependent
  • standardized
  • incorp. functional, struct and microsructural info

Day 2 - Tuesday, October 14 2025 – Oral session 2

Cross-species Standardised Cortico-Subcortical Tractography

• XTRACT protocols for bundles guided by tracer data.
• Amygofugal tract, anterior commissure, muratoff, striatal bundle
• The relative positioning of tracts mirrors tracer data.
• Comparison between twin pairs shows agreement.

Mapping the Superior Longitudinal System: anatomical insights from BraDiPho - Laura Vavassori

Validation of arcuate fasciculus tractography in Broca’s area using cortical stimulation language mapping in a paediatric epilepsy surgery case - Joseph Yang

• Compare manual Arcuate Fasciculus tractography with automated Arcuate Fasciculus tractography.
• Validation by comparing stimulation sites with the Arcuate Fasciculus.

Unveiling the functional specialization of human circuits with naturalistic stimuli - Marcela Ovando-Tellez

• What is the functional specialization of White Matter?

Day 3 - Wednesday, October 15 2025 – Opening session

Keynote 1 : Marco Catani - Connectional anatomy before and after tractography

• Arcangelo Piccolomini — first to differentiate white and gray matter
• Catani M and Thiebaut de Schotten M., 2008 — “A diffusion tensor imaging tractography atlas for virtual in vivo dissections.”
• Catani M et al., 2005 — “The rises and falls of disconnection syndromes.”
• Frontal aslant tract — Name was originally coined informally; involved in speech initiation and characterized with tractography.
• Inferior fronto-occipital fasciculus is not a semantic pathway (papers rejected)
• “The longer are the streamlines, the deeper they are in the brain” Meynert’s rule confirmed by tractography
• “Poppy hand region”
• Penfield W and Boldrey E., 1937 — “Somatic motor and sensory representation in the cerebral cortex of man as studied by electrical stimulation.” brain -> function, Catani Brain 2017 “What works together is wired together”
• Wedeen VJ et al., 2012 — “The geometric structure of the brain fiber pathways.” (sheetography)
• Single axons can make ninety-degree turns; entire bundles do not typically turn as a unit.
• Nomina Anatomica — Tract names derived from tractography.
• Catani atlases (with Michel Thiebaut de Schotten and Dell’Acqua). ### Power pitches:
• Tractome 2.0
• Sam. Deslauriers : principled approach tractography, equations of tractography ### Round tables: Application and translational aspects of tractography - Kathryn Manning

Day 4 - Thursday, October 16 2025 – Opening session

Keynote 1 : What can we expect from tractography in brain surgery ? - Hughes Duffau

• A tumor mass does not exist in isolation; it is part of a distributed network.
• A focal lesion can have effects across the entire brain network.
• Herbet G et al., 2020 — “Revisiting the Functional Anatomy of the Human Brain: Toward a Meta‑Networking Theory of Cerebral Functions.”
• Clinicians prioritize outcomes and reliability over complex tractography visualizations.
• Broca’s area is not the sole ‘speech center’; language production relies on distributed networks.
• Arcuate fasciculus: role discussed in the context of distributed language and repetition pathways.
• Cortical terminations of the Inferior fronto‑occipital fasciculus and the uncinate fasciculus were reviewed (frontal, temporal, and occipital targets).
• Martino J et al., 2010 — “Anatomical dissection of the inferior fronto‑occipital fasciculus.”
• Sarubbo S et al., 2015 — “Towards a functional atlas of human white matter.”
• Engelhardt E et al., 2010 — “Cerebrocerebellar system and Arnold’s bundle.”