Long-term memory is one of the most basic cognitive functions. Only in the last thirty years has it become apparent that long-term memory is not a single system, but that there are multiple types of long-term memory that are available to humans and other mammals. The basic distinction between declarative memory - the memory system that we usually think of when talking about memory in a casual way - and non-declarative memory is essential for the understanding of remembering. Even patients without any ability to form new declarative memories can still learn - but they have to use their skill-based memory systems to do so and they don't have a conscious awareness of their memories. Dr. Squire and others have identified the medial temporal lobe as the main structure involved in the formation of declarative memories both in humans as well as other mammals (e.g., rodents, monkeys), while non-declarative memories are supported by independent structures that are often unaffected by damages to the medial temporal lobes.