It appears possible to stimulate the production of the hormone leptin to suppress appetite and stimulate neuron development with frequencies in the 4mhz range. These frequencies appear to vary slightly across individuals and more research is needed.
Leptin regulates brain growth: Studies of leptin-deficient mice reveal new roles for the hormone in the hypothalamus
By David Secko, April 2, 2004, The Scientist
In the 10 years since the discovery of the hormone leptin and its appetite-suppressing activity in mice, the hormone has provided a good deal of insight into how a metabolic signal can affect the central nervous system. In the April 2 Science, two papers report that leptin regulates synaptic plasticity and neuronal development.