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. Author manuscript; available in PMC: 2018 Jun 7.
Published in final edited form as: Neuron. 2017 Jun 7;94(5):954–960. doi: 10.1016/j.neuron.2017.04.044

Figure 2.

Figure 2

Examples of discrete symmetry breaking in biology. (A) Two mutually exclusive genetic codes: with similar binding profiles. The top 2×2 matrix corresponds to standard base pairing, and the bottom right 2×2 matrix is an alternative code with notations from (Piccirilli et al., 1990). Binding affinities are denoted by color and approximate binding strengths based on the model from (Wagner, 2005). The two codes are mutually exclusive because of strong mixed binding (off-diagonal blocks). (B) Optimal encoding based on two (or more) distinct thresholds (orange and yellow curves here) requires sharper activation functions compared to encoding based on a single type of nonlinearity (blue). Further, the activation function (orange) whose threshold is closer to the peak of the input distribution (gray) should be sharper than the activation function with a larger (further removed from the peak) threshold (yellow). The theoretical approach can be applied to encoding by neurons or intracellular receptors.