The Scharfman laboratory also is interested in the mechanisms underlying plasticity, such as the ability of the brain to make modifications to neuronal structure (axon sprouting or retraction, spine growth) and synaptic strength (long-term potentiation and depression). We are therefore interested in a number of trophic or growth factors such as the neurotrophins (BDNF) and steroids (estrogen, androgen) which modulate plasticity. The recognition that new neurons are generated throughout life (postnatal neurogenesis) have fostered our interest in adult neurogenesis also, especially in the dentate gyrus, where a number of normal functions appear to be controlled. The diverse types of plasticity in the brain allow us to learn and form memories, respond to a changing environment, and recover from injury or illness. In general, we hypothesize that neurological and psychiatric disease is in part due to abnormalities in plasticity, such as excessive responses to BDNF, which we think contributes to temporal lobe epilepsy, and aberrant neurogenesis, which we hypothesize is a reason for psychiatric illness.