To form memories, humans must create synapses, or connections between brain cells, that encode sensory information from an event into our memory. From there, our brains organize that information into categories and link it to other similar data, which is called consolidation. In order for that memory to last, we must periodically retrieve these memories and retrace those initial synapses, reinforcing those connections.
Studies have largely refuted the long-held thinking that babies cannot encode information that forms the foundation of memories. For instance, in one experiment involving 2- and 3-month-old infants, the babies' legs were attached by a ribbon to a mobile [source: Hayne]. By kicking their legs, the babies learned that the motion caused the mobile to move. Later, placed under the same mobile without the ribbon, the infants remembered to kick their legs. When the same experiment was performed with 6-month-olds, they picked up the kicking relationship much more quickly, indicating that their encoding ability must accelerate gradually with time, instead of in one significant burst around 3 years old.
This memory encoding could relate to a baby's development of the prefrontal cortex at the forehead. This area, which is active during the encoding and retrieval of explicit memories, is not fully functional at birth [source: Newcombe et al]. However, by 24 months, the number of synapses in the prefrontal cortex has reached adult levels [source: Bauer].
Also, the size of the hippocampus at the base of the brain steadily grows until your second or third year [source: Bauer]. This is important because the hippocampus determines what sensory information to transfer into long-term storage.
But what about implicit memory? Housed in the cerebellum, implicit memory is essential for newborns, allowing them to associate feelings of warmth and safety with the sound of their mother's voice and instinctively knowing how to feed. Confirming this early presence, studies have revealed few developmental changes in implicit memory as we age [source: Newcombe et al]. Even in many adult amnesia cases, implicit skills such as riding a bicycle or playing a piano often survive the brain trauma.
Now we know that babies have a strong implicit memory and can encode explicit ones as well, which indicates that childhood amnesia may stem from faulty explicit memory retrieval. Unless we're thinking specifically about a past event, it takes some sort of cue to prompt an explicit memory in all age groups [source: Bauer]. Up next, find out what those cues are.