arXiv:2603.03347v1 Announce Type: new Abstract: Synapses are efficient in the sense that their natural conductance values convey as many bits per Joule as possible, but efficiency falls rapidly if the conductance is forced to deviate from its natural value (Harris et al, 2015). However, the exact manner in which efficiency falls as conductance deviates from its natural value remains unexplained. Here, we express the minimal energy boundary proposed in Malkin et al (2026) in terms of Shannon's information theory (Shannon, 1949) to derive a biophysically motivated model that accurately predicts the decrease in efficiency values observed in Harris et al (2015) across a wide range of synaptic conductances.