Hippocampus and trauma memory

The hippocampus is a bilateral subcortical structure of the medial temporal lobe, essential for explicit memory (conscious, narrative, autobiographical) and for the temporal integration of experiences. Without a functional hippocampus, we cannot form new autobiographical memories; experiences remain in implicit memory but are not integrated into the conscious narrative.

In acute and chronic trauma: during severe traumatic experiences, high levels of cortisol and glutamate can inhibit hippocampal function. The consequence: the traumatic event is registered by the amygdala (implicit emotional memory) but not by the hippocampus (explicit narrative memory). This is why many survivors remember 'feeling something terrible' without being able to narrate exactly what happened —especially in early trauma—.

Neuroscientific findings: MRI studies in PTSD victims show a smaller hippocampal volume compared to controls. Causality is still debated (does trauma reduce the hippocampus or does a smaller hippocampus predispose to trauma?), but the correlation is robust. Studies with Holocaust survivors and their descendants show similar patterns.

Clinical implication: explains the phenomenon of 'frozen memory' in trauma —images without clear temporal context, the sensation of 'it's still happening' even though the event was decades ago, difficulty integrating the trauma into the autobiographical narrative—. Therapeutic work seeks, in part, to restore hippocampal integration: to place the trauma in its time, in its context, as an event that happened and ended.

Good neuroplasticity news: the hippocampus is one of the brain structures with the greatest capacity for adult neurogenesis —it produces new neurons throughout life—. Exercise, adequate sleep, BDNF (neurotrophic factor), and effective therapy promote this neurogenesis. Trauma healing includes documentable hippocampal reconstruction.