Shorter sleep duration may also contribute to cognitive decline through degeneration of the hippocampus through multiple pathways, including changes in neuronal excitability, decreasing synaptic plasticity, and decreasing neurogenesis. Sleep deprivation activates neurotoxic complement components C3a and C5a, which disturb the hippocampal brain-derived neurotrophic factor (BDNF) pathway and adult neurogenesis, eventually impairing spatial memory. The gene discussed is BDNF; the disease is Mental deterioration.