Fig. 1.

Schematic representation of the Marr motif. Four sensory neurons at the left (circles represent their cell bodies) send their axons to two regions of neuropil (dotted circles) in the first (encoder) stage of the three-stage circuit. Additional circuitry (not illustrated) produces interactions between the two neuropil regions. Dendrites of the two stage 1 projection neurons (cell bodies of precerebellar neurons are the circles) collect and format the sensory information as a combinatorial code. This coded information is then sent over the precerebellar neuron axons to stage 2 (decoder). Synaptic connections (dark dots) are made on the dendrites of four stage 2 neurons (granule cell bodies represented by four circles), and the output, the broken code, is sent at the right of the diagram to stage 3 (not represented). Additional circuitry responsible for breaking the combinatorial code in the second stage is not shown.