This 2011 human study by the grandfather of hippocampus stress studies, Martin Teicher, quantified childhood maltreatment using the Adverse Childhood Experiences study and Childhood Trauma Questionnaire scores:
“The strongest associations between maltreatment and volume were observed in the left CA2-CA3 and CA4-DG subfields, and were not mediated by histories of major depression or posttraumatic stress disorder.
These findings support the hypothesis that exposure to early stress in humans, as in other animals, affects hippocampal subfield development.”
The evidence is clear that early emotional experiences change our brains. There are seldom valid reasons for researchers to exclude emotional content when designing human brain studies, especially studies that involve the hippocampus.