In this talk, I will present two complementary studies: understanding how the dendrites of cortical neurons process synaptic information and developing new tools to investigate their function in human brain tissue. In the first part, I will present new results showing that dendritic spikes are widespread among cortical inhibitory neurons across different layers, cell types, and mammalian species, including humans, domestic pigs, and rats. I will also compare the dendritic integration strategies of excitatory and inhibitory neurons. Using computational modeling, I will demonstrate how synaptic clusters on dendrites of different neurons, electrically coupled through gap junctions, can interact to form higher-order functional units. Together, our findings suggest that local dendritic spikes are a pervasive mode of neocortical operation. In the second part, I will present a complementary technological advance addressing the challenges of time-sensitive experiments and short-lived tissue preparations. Our approach, based on Semliki Forest virus (SFV), enables transgene expression within 4–6 hours, allowing fluorescent labeling and optogenetic activation of neurons in freshly resected human brain tissue. This makes functional experiments possible within 24 hours of transduction, opening new opportunities to study human cortical circuits.