Those four year old events might as well have occurred forty years ago.
Maybe this is why ...
Scientific American: Mind the Alzheimer's SwitchIt's one of the lesser sorrows of parenting -- much of what one treasures as a parent is forgotten to the child. I'd long suspected it was due to brain rewiring occurring during childhood. Now the evidence is emerging.
... neuroscientists at the Buck Institute in California made a startling discovery—young brains may experience memory loss due to the same mechanism responsible for Alzheimer's, but this memory loss could give young brains the ability to rewire. They say all brains may have a forward-reverse switch for making and breaking memories, but in certain older brains this switch can go awry, leading to Alzheimer's.
A protein called APP could control the switch. The researchers previously found they could stop Alzheimer's in mice by preventing APP from being cut in two. Recently they found that YOUNG brains have ten times more cut APP than the diseased brains of Alzheimer's patients—and you'd think that was a bad thing. But this isn't detrimental to young brains because they are constantly rewiring to make new neural connections—so some broken memories along the way don't hurt.