Click here to get the ‘Part 5: BPPV Nomenclature is Canal-Based — NOT Muscle Based’ handout

The posterior canal connects to the ipsilateral Superior Oblique (SO) and contralateral Inferior Rectus (IR) — muscles that pull the eye DOWN.

So why does posterior canal BPPV produce UPbeating nystagmus?

If you’ve ever paused mid-explanation, trying to reconcile muscle actions with nystagmus direction — same. This is the paradox we’ve been building toward all series.

Part 5 of our Visual-Vestibular Foundations Series resolves this by connecting everything we’ve learned:

→ Conjugate gaze and muscle actions (Part 1)

→ Synergistic patterns (Part 2)

→ Canal-to-muscle VOR connections (Part 3)

→ The two-phase nature of nystagmus (Part 4)

The answer: BPPV nomenclature is canal-based, not muscle-based.

The muscles DO pull down — that’s the slow phase (the true vestibular response). But we NAME nystagmus by the fast phase (the saccadic reset).

Once you trace the complete mechanism — from otoconia displacement through Ewald’s Laws to what you actually observe — the paradox dissolves.

I’ve attached a deeper dive that walks through the step-by-step mechanism and includes a summary table for all canal variants.

Clinicians who understand WHY posterior canal BPPV produces upbeating nystagmus — rather than memorizing patterns — can confidently interpret atypical presentations, recognize red flags, and troubleshoot failed repositioning maneuvers.

That’s the power of understanding mechanism over memorization.

Thank you for following this 5-part series! The foundation is built. Now go apply it.

By Bridgett Wallace, PT, DPT ~ 360 Neuro Health Co-Founder & Director of Clinical Education