Poisson ISI: p(t) = λe-λt
Gamma (refractory):
p(t) = tk-1e-t/θ/(Γ(k)θk)
CV = σ/μ — coefficient of variation
CV=1: Poisson; CV<1: regular; CV>1: bursty
Fano factor: F = σ²_N/μ_N
Gamma (refractory):
p(t) = tk-1e-t/θ/(Γ(k)θk)
CV = σ/μ — coefficient of variation
CV=1: Poisson; CV<1: regular; CV>1: bursty
Fano factor: F = σ²_N/μ_N
ISI distribution reveals neural coding strategy: clock-like (sensory), Poisson (cortical), or bursty (limbic). Refractory period enforces minimum ISI, lowering CV below 1.