When a person blacks out (especially from alcohol), the hippocampus is unable to properly form and store new memories, so events that happen during the blackout are not recorded into long‑term memory. This is why someone can appear awake, talk, walk, and make decisions, yet later have no recollection of what they said or did.

Quick Scoop

  • The hippocampus is a small brain structure deep in the temporal lobes that helps turn short‑term experiences into long‑term, autobiographical memories.
  • During an alcohol blackout, high blood‑alcohol levels disrupt hippocampal neurons and key receptors (like NMDA receptors), so memory consolidation “shuts down” even though other brain areas are still working.
  • The result is a “gap” in memory: it is not that the memory is hidden or repressed, but that the brain never successfully stored it in the first place.

What the hippocampus is “unable” to do

In the specific phrasing “when a person blacks out, their hippocampus is unable…”, the missing idea is “to form or consolidate new memories.” It is not mainly about regulating blood pressure or controlling muscles; those functions are handled by other brain regions and can remain relatively intact during a blackout.

Why this matters

  • Frequent blackouts signal that alcohol use has reached a level that can damage brain structures, including the hippocampus, and may contribute to long‑term learning and memory problems.
  • Even a single severe blackout can be associated with risky behaviors (injuries, unsafe decisions) that the person will later be unable to remember, increasing both medical and safety risks.

In short, during a blackout the hippocampus is unable to effectively consolidate short‑term experiences into long‑term memories, so the “record button” for new memories is essentially switched off.

Information gathered from public forums or data available on the internet and portrayed here.