Siyar Bahadir, MD, PhD(c)

Neurosurgeon.
Scientist.
Builder.

I am a neurosurgeon and PhD candidate at the Feinstein Institutes in New York. I study human anatomy and build ways to see, measure and explore it—from the cells and fibers of the vagus nerve to the brain’s fluid spaces and the shape of a reconstructed skull.

My work moves between dissection, microscopy, medical imaging, software and 3D printing. The two projects at the heart of my PhD are the human vagus branch atlas and the three-dimensional microanatomy of the nodose ganglion and vagus nerve. My current collaborations extend that approach to cranial reconstruction, ultrasound imaging and connectome-informed treatment planning.

Three-dimensional reconstruction of a human nodose ganglion with colorful fibers, cells and vessels
THE HUMAN NODOSE GANGLIONA whole sensory world,
inside a few millimeters.See the research
Actual research reconstruction
400+Operations
130+Brain tumor operations
80+Spinal operations
25+Cranial reconstructions
More about my surgical career Hacettepe University · 2017–2023

130+ Brain tumor operations

35 glial tumor resections · 30 navigation-guided resections · 10 posterior fossa procedures · 13 metastatic tumor procedures · skull base, pituitary, brainstem and intraventricular surgery.

25+ Cranial reconstruction operations

21 operations involving plate-based reconstruction · 3 autologous graft cranioplasties · 2 implant-based cranioplasties.

80+ Dural reconstructions

74 galeal graft repairs · 7 fascia lata graft repairs · 1 skull base dural repair.

80+ Spinal operations

30 lumbar microdiscectomies · cervical, thoracic and lumbar decompression · spinal tumors · instrumentation and fusion · spinal vascular surgery.

80+ CSF diversion operations

30 shunt placements · 21 shunt revisions · 6 third ventriculostomies · ventricular and lumbar drainage.

25+ Functional & epilepsy operations

9 vagus nerve stimulator implantations · 1 deep brain stimulation procedure · epilepsy resections · cortical stimulation and electrocorticography · intracranial electrode placement.

45 Hematoma & decompression operations

Subdural, epidural and intracerebral hematoma evacuation · 9 decompressive craniectomy operations.

17 Aneurysm operations

Single- and multiple-aneurysm clipping procedures.

8 awake craniotomies · 90+ pediatric operations

Counts reflect currently available surgical records from 2019–2023. Records from 2017–2019 and additional emergency procedures are not yet included. Procedure breakdowns may overlap within an operation and across categories.

Selected work

Anatomy, experiments & surgical questions

Beginning with the two projects at the heart of my PhD, followed by the clinical questions that have shaped my work.

PhD research

Inside the human nodose ganglion & vagus nerve

The nodose ganglion contains sensory neurons that carry information from our organs to the brain. During my PhD in the Translational Neurophysiology Lab at the Feinstein Institutes for Medical Research, led by Stavros Zanos, I have been working to understand how those cells and their fibers are organized in three dimensions.

Together with Stavros Zanos, with help from Eric Chang, PhD, and Ibrahim Mughrabi, PhD, I developed a workflow spanning human tissue preparation, clearing, immunostaining, whole-specimen light-sheet microscopy and computational reconstruction. I develop image-analysis tools to trace fibers and map cells, alongside innovative 3D-printing applications for light-sheet microscopy.

This is hands-on work across dissection, advanced imaging and computational anatomy. It has grown into studies of microanatomy and surgical access, with invited presentations at Rockefeller University and the Center for Pain Studies at UT Dallas.

Figures from my Bioelectronic Medicine Summit 2026 poster, “The Viscerosensory Gateway.”

PhD research

A human vagus nerve branch atlas

Alongside the microscopic work, I wanted to map the vagus nerve at the scale a surgeon encounters it: where its branches leave the main trunk, which organs they reach, and how that anatomy varies between people.

With Stavros Zanos and our team, I turned thousands of anatomical branch observations into a standardized, surgically relevant map. The project brings together human dissection, quantitative anatomy and software in a Brain Stimulation paper, open data and analysis, and an interactive atlas that others can explore.

NIH SPARC invited a dedicated seminar on the atlas. Together with the nodose and fiber-reconstruction work, it forms the core of my PhD: understanding human vagus anatomy from organ-specific branches down to cells and fibers.

Human Vagus Nerve AtlasOpen full screen
Branch emergence map from the Human Vagus Nerve Atlas

If the viewer does not load here, use “Open full screen.”

Try it

Select a branch group and follow where it emerges along the nerve. Compare the distribution across the cohort.

Clinical experience · U.S. collaborations

Developing surgical technologies and brain mapping

From the operating room to simulation, tractography and surgical tools.

My work in surgical technology grew out of clinical neurosurgery. During my training at Hacettepe University (2017–2023), I logged more than 450 operations, integrated MRI, tractography and 3D reconstruction into surgical planning, and co-developed a laboratory for microsurgical simulation and skills training. I subsequently practiced as an attending neurosurgeon in Anamur.

Across these years, collaborations with U.S.-based neurosurgeons and brain-mapping researchers became a continuing part of my work: making anatomy easier to explore, operations easier to plan, and surgical outcomes easier to measure.

2021 · Brain mapping

Connectome research with Frank Yeh

Working with a team that included Frank Yeh, founder of DSI Studio, I performed the connectome analysis and built the 3D visualizations for our study of human brain connectivity. I also co-wrote the initial manuscript. We examined how network hubs differ across hemispheres and within anatomical parcels.

Read the connectome study ↗
2023 · Surgical simulation

A virtual anatomy laboratory with Barrow

With Nicolás Gonzalez-Romo and collaborators at Barrow Neurological Institute, I contributed to a collaborative virtual neurosurgery anatomy laboratory. The team brought reconstructed anatomical specimens into a shared VR environment for remote exploration and surgical education.

Read the virtual anatomy study ↗
2025 · Augmented reality

Tractography with Michael Ivan’s group

I built the tractography reconstructions for our augmented-reality cranial surgery work with Michael Ivan’s group at the University of Miami, contributing the white-matter anatomy used in surgical planning and visualization.

Read the augmented-reality paper ↗
2025–2026 · Cranial reconstruction

Measuring reconstruction with Netanel Ben-Shalom

With Netanel (Nati) Ben-Shalom, I developed automated 3D measurement and topographic analysis to quantify cranial deformity and its correction after cranioplasty. My work connected registration of head models, geometric measurements and visual maps of surgical change.

The paper is accepted in Operative Neurosurgery. I presented the work orally at CNS and at the neuroplastic surgery meeting at Lenox Hill Hospital.

CNS oral presentation abstract ↗
Residency research · ongoing collaborations

iNPH & Cistern Explorer

My neurosurgery thesis at Hacettepe developed a comprehensive volumetric analysis of the brain and its cerebrospinal-fluid spaces in idiopathic normal-pressure hydrocephalus (iNPH), combining quantitative MRI with detailed 3D anatomical models.

Together with Brazilian researchers, we later extended the dataset and analysis pipeline into three presentations at the Hydrocephalus Society conference, with one of our collaborative projects receiving an award. The methods also remain in use in Turkey.

I later built Cistern Explorer around those anatomical reconstructions, combining 3D anatomy and anatomical sections with an exploratory CSF-flow model. Place a catheter, introduce a tracer and inspect its spread through the modeled spaces. The fluid simulation is a later extension of the original thesis work.

This is a research demonstration for exploring model behavior, rather than a validated prediction of an individual patient’s CSF physiology.

Cistern ExplorerOpen full screen
Preview of Cistern Explorer

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3 Hydrocephalus Society presentations · 1 award-winning project
Interactive anatomy · surgical education

Neuroplastic Anatomy — from 3D anatomy to surgical illustrations

I built Neuroplastic Anatomy to explore the layered anatomy of the scalp and head, and turn a chosen anatomical view into a surgical illustration. It grew from my collaboration with the Society for Neuroplastic Surgery.

Rotate the model, reveal or hide structures, adjust labels and separate the layers to understand how they fit together. The drawing workspace uses the arranged 3D view as the starting point for an anatomical illustration.

Neuroplastic AnatomyOpen full screen
Neuroplastic Anatomy application showing the layered anatomy of the scalp and head with structure controls

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3D anatomy · anatomical illustration · education

Ultrasound — learning from sparse annotations

With Netanel Ben-Shalom at Lenox Hill Hospital, whose work includes transcranioplasty ultrasound through sonolucent implants, I built a rapid ultrasound annotation and segmentation tool. It trains random forests from sparse annotations, designed around the limited input a clinician could realistically provide in the operating room.

My contribution was hands-on implementation: turning the annotation workflow and machine-learning approach into a usable research tool. The study is available as a medRxiv preprint and has been submitted to a journal. I also contribute to the group’s broader transcranioplasty-ultrasound research.

Image analysis · random forests · clinician-facing software

medRxiv preprint · October 2026 · Manuscript submitted to a journal

MRI–Ultrasound Explorer

I built an interactive imaging workspace that brings registered MRI and intraoperative ultrasound into a shared 3D scene, alongside reference white-matter pathways and cortical regions. Linked views let researchers inspect the ultrasound window in its wider anatomical context.

The example below combines RESECT MRI/ultrasound with mapped population-reference tractography and HCP-MMP cortical regions. The pathways and regions provide anatomical context; they are not structures directly measured by ultrasound.

Registration · tractography · anatomical visualization · web engineering

Interactive research demo. Explore the registered images and reference anatomy below.

Data: RESECT (CC BY 4.0); Yeh population tractography atlas (CC BY-SA 4.0); HCP-MMP cortical regions under WU-Minn HCP data-use terms. Figures include registration, reslicing and visualization adaptations; shared under CC BY-SA 4.0 where applicable.

MRI–Ultrasound ExplorerOpen full screen
Preview of MRI–Ultrasound Explorer

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BrachyAtlas — anatomy, connectivity & radiation planning

With A. Gabriella Wernicke and Netanel Ben-Shalom, I built BrachyAtlas to combine anatomy, imaging, implant geometry and radiation dose in one patient-specific intracranial brachytherapy workflow.

It integrates those inputs with an AI agent that helps the clinician work through complex anatomical and connectomic reports, bringing modeled radiation exposure and the surrounding brain anatomy into a shared view for research planning.

Research prototype
STEP 01 / 03
An implant that follows the anatomy

Arrange virtual tiles on the patient-derived surface. The opened planning map stays linked to the three-dimensional view, so placement can be inspected from both perspectives.

Output · Virtual tile and seed geometry

Views from Figures 2–4 of our BrachyAtlas preprint (2026). The anatomical views describe modeled exposure.

Research collaboration · Randy D’Amico’s group

Connectomic Anomaly — following connectivity over time

With Randy D’Amico’s brain-tumor group, I build tools to examine patient-specific connectivity anomalies and how they change across scans, surgery and treatment.

The Connectomic Anomaly Explorer brings connectivity matrices, regional and network-level measurements, and longitudinal comparisons into an interface the research team can explore directly.

Patient-specific connectomics · longitudinal analysis

Clinical AI — evaluating capability and limits

In 2024, I co-authored a Clinical Neurology and Neurosurgery study evaluating ChatGPT on brain-tumor diagnosis and treatment planning. I built the API-based system that sent clinical questions to the model and captured its answers for independent assessment by practicing neurosurgeons.

With Randy D’Amico, I later moved from benchmarking performance to a harder question: what happens when AI becomes part of the clinical cognitive system? That became our 2026 Neurosurgery letter on the extended mind and the uneven frontier of clinical AI.

We have also submitted a review to Neurosurgery on how AI studies should handle data quality, leakage, validation, interpretability, reproducibility and clinical meaning.

SIYAR / ON SCREENThe Vago channel ↗
SCIENCE, WITH A STORY

Meet Vago.

A small octopus.
A whole world inside us.

2 MIN · ANIMATED SHORT

Choose your next watch

Vago · animated science

Your organs have feelings

Your organs have feelings, too.Meet Vago and explore the messages traveling between our organs and brain.

The biology of inner balance

The biology of inner balanceA visual story about homeostasis and the feedback loops that keep us steady.

Neuroplastic surgery

Your skull is getting an upgrade

Your Skull Is Getting an UpgradeA visual introduction to neuroplastic surgery and neurotechnology in the skull.

Beyond brain surgery

Brain Surgery Changes More Than the BrainA visual introduction to the wider impact of brain surgery and the role of neuroplastic surgery.

Talks & conversations

Mapping the human vagus nerve

Mapping the human vagus nerveThe branch atlas, the anatomy behind it, and its relevance to selective neuromodulation.

The vagus nerve revolution

The vagus nerve revolutionMy conversation with Deborah Westphal about neurosurgery, mapping and bioelectronic medicine.

Caravan Wellness

5 Min How The Brain & Immune System Talk04:54 ↗

Brain & immune system

5 Min How The Brain & Immune System TalkBrain–immune communication and the inflammatory reflex.Caravan Wellness · Subscription required
5 Min Microglia & Aging05:48 ↗

Microglia & aging

5 Min Microglia & AgingThe brain’s immune cells and their changing roles with age.Caravan Wellness · Subscription required
5 Min What Is Cellular Senescence?05:43 ↗

Cellular senescence

5 Min What Is Cellular Senescence?An introduction to cellular senescence and aging.Caravan Wellness · Subscription required
3 Min The Vagus Nerve & Longevity04:06 ↗

Vagus nerve & longevity

3 Min The Vagus Nerve & LongevityA lesson exploring the vagus nerve in the context of aging.Caravan Wellness · Subscription required
5 Min Why The Brain Ages Differently From The Body05:01 ↗

Why the brain ages differently

5 Min Why The Brain Ages Differently From The BodyHow aging affects the brain and its cells.Caravan Wellness · Subscription required
AN ILLUSTRATED SERIES · 8 REFLEXES

Neuroscience ×
bioelectronic medicine.

One reflex at a time. My visual guides follow the anatomy, the signal and the response—making the body's hidden conversations easier to see.

THE REFLEX COLLECTION · 01 / 08

The vagus brake

A rise in blood pressure stretches arterial sensors. This rapid feedback loop adjusts the heart and blood vessels to steady pressure from one beat to the next.

01 / Trigger
More stretch in the aortic arch and carotid sinus as arterial pressure rises.
02 / Pathway
Aortic signals travel through the vagus; carotid signals travel through the glossopharyngeal nerve. Both reach the nucleus of the solitary tract in the brainstem.
03 / Response
More cardiac vagal activity and less sympathetic activity slow the heart and reduce vascular resistance.

The illustration focuses on the aortic, vagal arm of a reflex that also includes the carotid sinus.

EXPLORE THE COLLECTION
The poster wall

Research, in one big picture.

Posters from my human vagus and nodose research, including experimental methods, surgical access and literature curation. Select a poster to read it in the on-page viewer.

Bioelectronic Medicine Summit · 2026

The Viscerosensory Gateway

Whole-ganglion 3D anatomy of the human nodose ganglion at cellular resolution.

NYC Neuromodulation · 2026

Human nodose spatial transcriptomics

Organ-related expression of ion channels by vagal sensory neurons.

Literature curation · Hofstra / Feinstein

Curation of knowledge for vagal connectivity

Organizing vagal research through semantic similarity, text embeddings and vector spaces, alongside structured literature review.

Explore this work

Approach. Database searches and textbook sources feed a collaborative Covidence screening workflow, with quality assessment informed by PRISMA and AQUA.

What it shows. Text embeddings represent papers in high-dimensional vector spaces, where distances reflect semantic similarity. Lower-dimensional projections help visualize related topics and explore the literature. The poster also investigates language models for data extraction and quality assessment, with performance under evaluation.

Human peripheral nerve microanatomy

3D cytoarchitecture of human ganglia and nerves

A pipeline for building scalable 3D cytoarchitecture models from cleared intact fixed whole human ganglia and peripheral nerve samples.

Explore this work

Approach. CLARITY clearing and light-sheet microscopy of a human nodose ganglion with proximal vagus nerve, followed by random-forest pixel classification, surface reconstruction, cell segmentation and semi-automated fiber tracking.

What it shows. The reconstructions bring cell bodies and long, tightly packed axons into the same 3D spatial context, providing a foundation for studying peripheral nerve organization and targeted stimulation.

Elmezzi poster competition · 2025

Minimally invasive access to the human nodose ganglion

A proof-of-concept cadaveric photogrammetry study for tissue harvesting and potential electrode placement.

Explore this work

Approach. Layered dissection and co-registered 3D models guided route planning in one cadaver. External landmarks and custom craniometry then guided bilateral endoscopic access in a second cadaver.

What it shows. The marked sites were 7 mm from the left ganglion and 16 mm from the right. Incision, trocar placement, visualization and dyeing took less than 20 minutes on each side. These are preliminary cadaveric findings; electrode placement remains a future application.

Institutional poster record ↗

Vagus nerve research

Single-fiber tracking in the human vagus

Three-dimensional reconstruction of nerve fibers from microscopy images.

Original author and collaborator credits are preserved in each poster.

Connected through my AI harness

Research services & APIs.

I connect these research workflows through my AI harness and use them as API services across my projects—from image segmentation and registration to anatomical analysis and structured reporting. Contact me to explore a research collaboration.

Independent research service · API + browser demo

Disconnectome

A brain region or energy field in.
A structured report out.

I built Disconnectome as a reusable service for reporting on energy delivered to a defined region of the brain. A supplied region or spatial energy field is related to brain regions, reference pathways and functional networks, producing structured anatomical and connectomic output for other applications.

The service is designed around the spatial input, so it can support different energy-delivery workflows. The browser demo offers a hands-on way to explore the underlying lesion–pathway analysis.

01
Define the regionRegion or spatial energy field
02
Map the anatomyRegions · pathways · networks
03
Return the reportStructured output for the next tool

Illustrated service workflow

SEGMENT

Medical image segmentation

A research service that turns medical images and plain-language prompts into three-dimensional segmentation masks, ready for visualization and further analysis.

Image + text promptSegmentation masks
Contact for research collaborations ↗
ALIGN

Image registration

A registration service for bringing imaging into a shared coordinate space. It supports workflows that need to align scans with anatomical references before further analysis.

Image + referenceShared spatial coordinates
Contact for research collaborations ↗
PROCESS

Brain MRI segmentation & analysis

A research service for automated brain segmentation and anatomical analysis of T1 MRI. It returns regional segmentations and downloadable outputs for imaging research.

T1 MRISegmentation + downloadable outputs
Contact for research collaborations ↗
STRUCTURE

Document ingestion

A service that converts documents into a readable hierarchy and contextual text chunks. Inspect tables, headings and page references, or retrieve the structured result through its API.

Document or URLStructure + contextual chunks
Contact for research collaborations ↗
From services to experiences

Other things I’ve built.

CerebroMap

An interactive brain atlas and visual stories connecting neuroanatomy to everyday experience.

Explore CerebroMap ↗

Outfold

A platform for sharing 3D models through QR codes and augmented reality, bringing research posters into the space around them.

Open Outfold ↗

Noospera

A searchable 3D map of AI conversation history, built to help people revisit ideas and see connections across their work.

Explore Noospera ↗
Open the work

Things you can explore.

Interactive anatomy, imaging and research tools. Pick a project and take a closer look.

Also explore CerebroMap.

Experience & credentials

Clinical, scientific and technical background

Training and roles behind the work above.

Experience

The Feinstein Institutes for Medical Research / Elmezzi Graduate School

Elmezzi Scholar · PhD Candidate, Bioelectronic Medicine | 2023–present · Manhasset, NY

Human translational neuroscience focused on the vagus nerve and peripheral nervous system, integrating human anatomy, microscopy, molecular biology, computational imaging, software and device development.

Anamur State Hospital, Turkish Ministry of Health

Attending Neurosurgeon | 2023 · Mersin, Turkey

Independent emergency neurosurgical, trauma and acute neurological care in a resource-conscious public hospital.

Hacettepe University Faculty of Medicine

Neurosurgery Resident · Chief Resident | 2017–2023 · Ankara, Turkey

Comprehensive neurosurgical training with 450+ operations across cranial, tumor, vascular, trauma, spinal and functional neurosurgery.

Turkish Ministry of Health — Korkut District Hospital

Rural Emergency Physician · Regional EMS Coordinator | 2015–2017 · Turkey

Frontline emergency care, triage, resuscitation, interhospital transfer and regional EMS coordination across an underserved rural region.

CerebroMap

Founder | 2022–2025

Computational brain mapping, tractography, automated MRI analysis, 3D visualization and cloud-based neuroimaging workflows.

Selected publications & work in press
Additional papers, posters, abstracts & talks
2025Augmented reality in cranial surgery: head-mounted fiber tractography for brain tumor surgery.Paper ↗
2023Virtual neurosurgery anatomy laboratory: collaborative remote education in the metaverse.Paper ↗
2022Traumatic subgaleal hematoma in Ehlers-Danlos syndrome.Paper ↗
2021Group-level ranking-based hubness analysis of the human brain connectome.Paper ↗
2020Emergency diagnosis and triage with artificial intelligence in intracranial hemorrhage.Paper ↗
2025Scalable 3D cytoarchitecture models from cleared intact human ganglia and peripheral nerve.Abstract ↗
2025Minimally invasive access routes to the human nodose ganglion.Poster ↗
2025Automated 3D Measurement and Topographic Representation for Cranioplasty. CNS oral presentation.Abstract ↗
2024Single-fiber tracking and 3D reconstruction of human vagus nerve trajectories. Minnesota Neuromodulation Symposium.Record ↗
2024Fascicular Organization and Fiber Composition of the Human Vagus Nerve at Levels of Branch Emergence.Abstract ↗
2022Volumetric Analysis of the Brain in Normal Pressure Hydrocephalus.
2026NIH SPARC invited seminar: human vagus nerve atlas.Video ↗
2026Rockefeller University Light Sheet Microscopy Workshop. Invited presentation.
2026Center for Pain Studies, UT Dallas. Invited presentation.
2026Neuroplastic & Reconstructive Surgery Symposium, Lenox Hill Hospital. Invited presentation on quantitative cranial-shape measurement.
Contact

Let’s talk about anatomy, research or something worth building.

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