// the brain · magnets

brain magnets

The brain as magnets. Imprint a picture and it becomes a valley in the field. Break the picture — flip half the magnets — and hit recall: each spin turns to match its neighbors, the energy only ever falls, and the whole thing slides back into the shape it remembers. Memory as a place the magnets want to be.

imprint:
temperature0.00

memories 0 · energy 0 · recalled — · empty

imprint a few · click + drag to draw your own, then break it and recall · red = north, blue = south · raise temperature to melt the memory

// the science under it

  • memory as magnetism. Treat neurons as spins that point up or down and pull their neighbors into line — the same math that describes a magnet. (Ising 1925; Little 1974)
  • imprinting is Hebbian. Storing a pattern means strengthening the link between magnets that agree in it: Wij += si sj / N. Each stored pattern becomes a low-energy valley. (Hopfield 1982, PNAS)
  • recall is rolling downhill. Flip each magnet to match the field around it and the energy E = −½ Σ Wij si sj never rises — so a broken cue slides into the nearest stored valley. That's associative memory: the whole from a fragment.
  • it can hold about 0.138 N. Past roughly that many patterns the valleys blur into spurious states and recall breaks down. (Amit, Gutfreund & Sompolinsky 1985)
  • temperature is noise. Raise it and the magnets flip at random (Glauber dynamics) — warm enough and the memory melts. The physics behind this won the 2024 Nobel Prize in Physics (Hopfield & Hinton).

// what this is not

  • neurons are not literally magnets. This is an abstraction — it shows how alignment can store and recall a pattern, not how a brain actually works.
  • this is also not a brain magnet in the medical sense — that's TMS, real magnetic pulses applied to the scalp (rTMS is FDA-cleared for depression). Different thing entirely; this is a memory model, not a device.

// sources

Ising 1925 · Little 1974 · Hopfield 1982 (PNAS) · Amit, Gutfreund & Sompolinsky 1985 · Nobel Prize in Physics 2024 (Hopfield & Hinton).