As pointed out by Hebb (1949) there is little reason to consider the issues of perceptual development and the issues of learning to be fundamentally differentwhether studying them as abstract cognitive processes or studying them at the microscopic, biological level. That is, regardless of how old an animal is, there

is the problem of how the brain uses experience to determine its own connectivity. With this perspective and with supporting evidence that implies synaptic modifi­ cation throughout the lifetime of an animal, we are comfortable interrelating observations from various times in the organism’s life to understand adaptive modifications of brain circuitry based on synaptic modification. Within this philosophy one question to consider is-What are the local modification rules used by neurons to control their own connections?