Experimental data indicate that cerebral energy consumption and synaptic density qualitatively correlate during development [1, 2], presumably indicating that energy plays a key role during the process. The purpose of this study is two-fold. First, to collect empirical data on cortical metabolism and synaptic density during development (from birth to adulthood for different mammals), and to quantify their dependence. Second, to provide atheoretical link between neural metabolism and electrical activities of neurons and synapses . A theoretical model allows us to estimate synaptic contribution to the overall energy used by neurons.