CA3 size predicts the precision of memory recall.

There is enduring interest in why some of us have clearer memories than others, given the substantial individual variation that exists in retrieval ability and the precision with which we can differentiate past experiences. Here we report novel evidence showing that variation in the size of human hippocampal subfield CA3 predicted the amount of neural interference between episodic memories within CA3, which in turn predicted how much retrieval confusion occurred between past memories. This effect was not apparent in other hippocampal subfields. This shows that subtle individual differences in subjective mnemonic experience can be accurately gauged from measurable variations in the anatomy and neural coding of hippocampal region CA3. Moreover, this mechanism may be relevant for understanding memory muddles in aging and pathological states.