Memories are lost because we have no recognizable need to reference the original experience. Memories are lost because of brain damage, loss of consciousness during an experience, neurochemical imbalance, cognitive restructuring, and sensory, emotional or hormonal overload. All the empirical evidence indicates that the more traumatic an experience the more likely one is to remember it. Novel visual images, which would frequently accompany traumas, stimulate the hippocampus and left inferior prefrontal cavity and will become part of long-term memory. Neuroscience tells us that a memory is a set of connections among groups of neurons that participate in the encoding process.
Encoding can take place in several parts of the brain.
Recollection of an event can occur by a stimulus to any of the parts of the brain where a neural connection for the memory occurs. If part of the brain is damaged, access to any neural data that was there is lost. On the other hand, if the brain is healthy and a person is fully conscious when experiencing some trauma, the likelihood that they will forget the event is near zero, unless either they are very young or they later experience a brain injury. Long-term memory requires elaborative encoding in the inner part of the temporal lobes. If the left inferior prefrontal lobe is damaged or undeveloped, there will be grave difficulty with elaborative encoding.