Fig 4. Effect of relative resting energy r on optimized energy efficiency η_opt(ρ).

(A, B) The optimized energy efficiency η_opt(ρ) vs. activity level ρ for various values of relative resting energy r in both binary (A) and analog scenarios (B). Larger r shifts the value of ρ_m for maximal η_opt(ρ) monotonically from ρ_m → 0 at r = 0 to ρ_m = 0.5 in binary scenario (open circles in (A)) or ρ_m = 1 in analog scenario (solid points in (B)) at r → ∞. (C) The monotonic dependence of ρ_m as well as its corresponding firing rate v (v = ρ/Δτ, Δτ = 20 ms) on r in both binary (black dashed line) and analog scenarios (black solid line). To achieve the maximal energy efficiency η_opt(ρ), the neuronal firing rate is constrained in the range of 1 ∼ 8 Hz for binary patterns (red dashed line) or 1 ∼ 10 Hz for analog patterns (red solid line) with r in the empirical range 0.005 ∼ 0.1, respectively.