Morpho-Temporal Decoupling: How Primate Neurons Expand Dendrites Without Losing Speed

During evolution, biological neurons scale computation by expanding dendritic branches. However, this expansion creates a biophysical dilemma: increased membrane area typically imposes a capacitive load that slows somatic dynamics and narrows temporal bandwidth. Here, we investigate how primate cortical neurons resolve this tradeoff. While primary basal dendrite number is relatively conserved across mouse cortical areas, it increases systematically along the primate cortical hierarchy. Using biophysically constrained multicompartment modeling, we identify a key dimensionless control parameter---the dendritic-to-somato-apical specific membrane resistance ratio, $\rho \equiv R_{m,\mathrm{dend}}/R_{m,\mathrm{sa}}$, that governs the coupling between dendritic morphology and the effective somatic time constant $\tau$. In mouse-like neurons ($\rho>1$), adding basal dendrites progressively increases $\tau$ and promotes reliable low-pass integration. Conversely, human-like neurons operate near a balanced-resistance regime ($\rho \approx 1$), where resistive reweighting counterbalances morphology-driven capacitive loading. This allows $\tau$ to remain nearly invariant despite expanded dendritic topology, shifting the structure-function tradeoff toward faster, more flexible coding with improved high-frequency tracking. Our results reveal a biophysical scaling principle linking evolutionary dendritic architecture to hierarchy-dependent coding, offering potential design rules for preserving temporal bandwidth in dendrite-inspired neuromorphic architectures.