Language Pathway (A→F→C)
A — Arcuate Fasciculus: Connects Wernicke's area (comprehension) to Broca's area (speech production). Linguistic intention forms here.
F — Frontal Aslant Tract: Links pre-SMA to Broca's area. Speech initiation and motor plan confirmation.
C — Corticobulbar Tract: Motor cortex to brainstem. Controls face, tongue, throat — semantics become physical speech.
Motor Pathway (C→S→C)
C — Corticospinal Tract: Primary motor cortex to spinal cord. Carries voluntary movement commands.
S — Superior Longitudinal Fasciculus: Connects frontal, parietal, and temporal lobes. Sensorimotor integration and spatial awareness.
C — Cerebellar Peduncles: Connect cerebellum to brainstem. Coordinate movement timing, precision, and motor learning.
The .trk files store only XYZ coordinates; colors are computed live from fiber direction.
You are looking at real white matter fiber bundles reconstructed from diffusion MRI. These pathways carry electrical signals between brain regions. Below are the two core circuits visualized here.
When you speak, your brain converts an abstract idea into coordinated muscle movements in under 600ms. This pathway traces that journey.
The brain's language highway. Connects Wernicke's area (where you understand words) to Broca's area (where you plan speech). When you think of what to say, this bundle carries the linguistic blueprint forward. Damage here causes conduction aphasia — you understand language and can speak fluently, but can't repeat words accurately.
Connects pre-SMA (supplementary motor area) to Broca's area. Acts as the "go signal" for speech — it confirms the motor plan and initiates the act of speaking. Damage causes speech initiation deficits: you know what you want to say but struggle to start saying it. Also involved in verbal fluency and turn-taking in conversation.
The final output. Projects from motor cortex to brainstem cranial nerve nuclei that control the muscles of the face, tongue, jaw, larynx, and pharynx. This is where the neural code becomes physical movement — your mouth shapes the sounds, your vocal cords vibrate, and meaning becomes audible speech.
Every voluntary movement — from picking up a cup to playing piano — relies on this circuit to translate cortical commands into smooth, precise actions.
The brain's main motor highway. Upper motor neurons originate in the primary motor cortex and descend through the brainstem to the spinal cord, where they synapse on lower motor neurons that directly activate skeletal muscles. About 90% of fibers cross to the opposite side (decussate), which is why the left brain controls the right body. Carries the raw movement commands.
A major association tract connecting frontal, parietal, and temporal lobes. SLF II links the dorsolateral prefrontal cortex to the parietal lobe — critical for spatial awareness and visuomotor integration. SLF III connects ventral premotor areas with the supramarginal gyrus — involved in grasping, tool use, and sensorimotor feedback. Together, they help you adjust movements based on what you see and feel.
The cerebellum receives a copy of every motor command and sensory feedback, then sends corrections back via the superior cerebellar peduncle (SCP). The middle cerebellar peduncle (MCP) carries input from the cortex to the cerebellum. Together they form a feedback loop: the cerebellum fine-tunes timing, coordination, and motor learning. This is why cerebellar damage causes ataxia — movements become clumsy and uncoordinated, not paralyzed.