Mission 2 · The story

How a fly knows which way it’s facing

Dror says: That way.

Morning. Light pours in through a gap in the shutters, and Dror wants out.

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WiredMind · Lesson 2

Push a real fly’s compass around and see what holds it in place.

About this lesson

Push a real fruit fly’s internal compass around, then silence the ring neurons and watch its sense of direction drift. A free 10-minute lesson.

1
Tap Stimulate to fire the left turn neurons (the turning signal). Then watch the compass dial.
The compass neurons (the heading cells) light up on one side. That bright patch, the bump, marks which way the fly faces.
2
Now tap Stimulate on the right turn neurons (the other signal). Keep your eyes on the bump.
The bump swung around the dial. Turning signals from each side push it opposite ways, so the fly’s sense of direction turns too.
3
Silence the ring neurons (the landmark carriers). They bring in what the fly sees. We will fire the right turning signal for you.
The bump slips off its spot and wanders. Without landmarks, the compass drifts.
4
Tap the ring neurons (the landmark carriers) button again to switch them back on. We will send the same turning signal.
The bump holds its spot again. Landmarks keep the fly’s compass true.

How do flies know which way they are facing?: A fly keeps an internal compass: a ring of neurons where one patch of activity marks its heading. Turns move the patch, and landmarks hold it steady.