This invention provides methods for determining whether an agent, known to upregulate the sonic hedgehog pathway, increases brain progenitor cell division in a subject. Furthermore, this invention provides methods for treating anxiety, depression, a cognitive disorder or a neuro-degenerative disorder or inhibiting the onset of anxiety, depression or a cognitive disorder by administering to an afflicted subject a therapeutically or prophylactically effective amount of the agent known to upregulate the sonic hedgehog pathway. Finally, this invention provides methods for treating anxiety, depression, a cognitive disorder or a neuro-degenerative disorder or inhibiting the onset of anxiety, depression or a cognitive disorder by administering to an afflicted subject a therapeutically or prophylactically effective amount of Hh-Ag 1.1, Hh-Ag 1.2, Hh-Ag 1.3, or a derivative of Hh-Ag 1.1, Hh-Ag 1.2 or Hh-Ag 1.3.