Graded action potentials in small cultured rat hippocampal neurons.

The 'all-or-nothing' principle has been central to neurobiology since the beginning of this century. We here demonstrate that action potentials in small cultured neurons from the hippocampus of rat embryos clearly depend on stimulus strength and thus deviate from this principle. We also demonstrate that similar stimulus-dependent action potentials can be predicted from computations based on voltage-clamp measurements. The findings suggest that amplitude modulation of the action potential may be a principle for information processing in the mammalian nervous system.