What is your earliest memory? Think about it. How far back in your past can you go and retrieve a clear memory? Most people can’t remember anything prior to age two or three. In explanation, Freud popularized the concept that people can’t remember anything before that as a result of repression (the unconscious preventing memory from entering conscious recollection). But today, neuroscience provides us with a more satisfactory explanation. We don’t remember anything earlier than age two to age three because the brain structures responsible for episodic memory (things personally experienced) aren’t sufficiently developed. Basically, we cannot remember anything prior to that early stage in our brain’s development because we possess no sense of self.Think of memory and identity like two dancers swaying to the music of time. Prior to age two, infants have no real identity and can’t recognize themselves in a mirror. Within a year after that, they will look at the mirror and reach up to touch a spot of rouge dubbed on their face moments earlier by an experimental psychologist. At that point they’re able to recognize that they are seeing in the mirror none other than themselves.By five years, all the memory systems are online and functioning. Coincident with the maturing of the pre-frontal cortex and hippocampus—they are both late maturers—episodic memory (for events that have been personally experienced) and semantic memory (general knowledge) emerge along with language. It is language that super charges the infant’s sense of identity. As remembered experiences slowly accumulate in the infant’s brain with the help of language, the components interweave into a fine tapestry composed of the skeins of identity and memory.The sequence is → words → concepts → identity → memories.Both episodic memory and semantic memory are based in the cortex, which is involved in a two-way communication with the hippocampus. Over our lifetime, the hippocampus along with the specialized memory centers in the cortex perform a kind of call and response routine. If we are trying to remember our college graduation, for instance, nerve impulses proceed from the hippocampus to the cerebral centers in the cortex where the memory is stored (the separate sights, sounds, discussions, etc). And then the separate components are wired back from the hippocampus, which recreates the graduation experience in the form of an episodic memory.Over time, identity, language, and memory create links between the present, the past, and the future. As a sign of life’s ironies and cruelties, these same communication channels unravel towards the end of life in the same sequence as they developed during the first five years. The initial indication of Alzheimer’s disease is usually a language problem, a loss for words (aphasia) and concepts, followed by the loss of identification for others, and finally, in the last sad stages of this dreadful illness, the failure to identify one’s self.There are different types of memories just as there are different types of dogs and cars. A poodle differs from a Great Dane, just as a Rolls Royce differs from a Prius. Each shares similarities to the other, but each also displays significant differences.Memory can divide it into transient and long-term. If you remember for only a few seconds something that you have just seen, heard, tasted, felt, etc., we speak of transient sensory memory. Unless you make a deliberate attempt to retain the fleeting impression thus created, transient memory, as the name implies, rapidly disappears. Memory for the taste of chocolate ice cream comes easily, but it’s difficult to maintain it in memory for more than a few seconds.