Where Gliomas Start — And Why Location Should Shape Surgery
Parietal lobe: the brain’s attention & visuospatial hub—why its networks matter in glioma surgery.
Post 3: Parietal Lobe
About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.
Why the parietal lobe matters
Parietal gliomas sit at the crossroads of attention, visuospatial control, touch and body position, and praxis (learned actions). Symptoms can be subtle: missing items on one side, losing the sequence of a task, or clumsiness with eyes closed. Mapping the right roads (white-matter tracts) helps teams remove more tumor safely.
Plain-English takeaway: Parietal tumors threaten how we aim attention and coordinate purposeful action. Protecting those circuits preserves independence.
Parietal networks in plain English
1) Dorsal Attention Network (DAN) — the spotlight controller
What it controls: Aiming your visual “spotlight,” scanning, and targeting.
Where it runs: Top/back parietal ↔ frontal eye fields (front↔back along the top).
Common signs: Slow visual search, overshooting when reaching, losing your place on a page.
2) Ventral Attention / Salience (VAN) — the interrupt/redirect
What it controls: “Hey—look there!” when something important appears.
Where it runs: Right inferior parietal/TPJ ↔ frontal insula/inferior frontal (lower-side).
Common signs: Hemineglect (often left-side neglect): half-shaved face, bumping doorframes, food left on one half of the plate.
3) Frontoparietal Control Network (FPN) via SLF II/III — the project manager
What it controls: Working memory, task switching, keeping steps in order.
Where it runs: DLPFC ↔ inferior/superior parietal (front↔back, top/side).
Common signs: “I lose the thread,” fatigue with multi-step tasks (cooking, paying bills).
4) Language–parietal hub (angular/supramarginal; arcuate/SLF) — the concept combiner
What it controls: Linking sounds to motor plans and binding concepts.
Where it runs: Inferior parietal ↔ temporal & frontal via the dorsal language stream.
Common signs (dominant side): Trouble repeating long phrases, reading multi-line text, retrieving abstract words.
5) Somatosensory pathways — the body map
What it controls: Touch and limb position (proprioception).
Where it runs: Thalamus → post-central gyrus/superior parietal; short links to premotor.
Common signs: “Cottony” numbness, misjudged limb position—worse with eyes closed.
6) Praxis network (left parietal ↔ premotor) — the blueprints for actions
What it controls: Learned tool use and gesture sequences.
Where it runs: Left inferior parietal to premotor via short parietofrontal fibers.
Common signs: Ideomotor apraxia—you know what to do, but the sequence falls apart (e.g., can’t mime using a comb on command).
7) Superior optic radiations — the “pie-on-the-floor” lane
What it controls: Lower-field visual information.
Where it runs: Superior visual fibers through parietal white matter to occipital cortex.
Common signs: Inferior quadrantanopia (missing the lower outer corner); tripping on curbs; skipping sub-lines when reading.
Common signs you might notice
Leaving food on the left side of the plate; missing text on the left of a page.
Can do each step but lose the sequence when making a meal.
Reaching overshoots unless eyes lock onto the target.
Knows the concept but can’t assemble the word under pressure.
Misjudges arm position with eyes closed.
“A corner of my view is missing”—especially lower-outer.
How teams plan surgery (Before • During • After)
Before surgery
Imaging the roads: Tractography of SLF II/III, arcuate, short parietofrontal fibers, and superior optic radiations.
Targeted testing:
Neglect: line bisection and cancellation
Attention/visual search tasks
Praxis: gesture/tool use on command
Executive: phonemic fluency, digit span (FPN)
Sensation: two-point discrimination and proprioception near S1
During surgery
Direct mapping (cortical & subcortical):
Watch for neglect-like behavior at TPJ/inferior parietal (often right-sided).
Test working memory/set-shifting near SLF II/III.
Check touch/proprioception near post-central and deep fibers.
Monitor visual fields when near superior optic radiations; adjust if transient cuts appear.
Awake vs asleep: Choose awake when attentional or praxis mapping is likely to change decisions.
After surgery
Neglect rehab: scanning, prism adaptation, cueing strategies.
Praxis/ADL: task chunking and external cues with OT.
Executive supports: checklists, timers, spaced breaks.
Sensory retraining: eyes-closed → eyes-open progression.
Visual field strategies: boundary scanning; safe-driving drills with therapy oversight.
Ask your surgeon (patient-facing)
Which attention network is closest to my tumor (dorsal vs ventral)?
How will you protect SLF II/III and the language–parietal hub?
Am I at risk for neglect, apraxia, or a visual field cut—and how will you test for them during surgery?
Which rehab steps start right after surgery?
Bottom line
Parietal gliomas live where attention, space, and skilled action meet. Understanding DAN/VAN, SLF/arcuate, praxis, somatosensory, and superior optic pathways lets teams push resection safely—preserving day-to-day independence.
Mini-glossary (quick definitions)
Hemineglect: Not attending to one side of space, even with normal eyesight.
Praxis / Apraxia: The ability (or difficulty) to carry out learned, multi-step actions.
Quadrantanopia: Loss of a quarter of the visual field (e.g., lower-outer corner).
SLF (Superior Longitudinal Fasciculus): Front↔back “highway” linking parietal and frontal areas.
TPJ (Temporoparietal Junction): A parietal “hub” that helps reorient attention.
Fast FAQ
Is neglect a vision problem?
No. Eyesight can be normal. Neglect is a failure to attend to part of space.
Why test tool-use and gestures?
They stress the praxis system. Subtle apraxia becomes obvious under command and guides safer resection.
Do all parietal surgeries cause visual field loss?
No. Risk depends on proximity to superior optic radiations. Imaging and subcortical testing reduce it.
