The Body Remembers Without Knowing It

A research group from Tohoku University and Iwate University has shown, through heart rate variability analysis, that the body freezes during disaster footage and that the sympathetic nervous system surges sharply once the footage ends. The response occurred even when viewers reported no subjective distress.

Photo by Joshua Chehov on Unsplash

This article was originally published in Japanese on Ki to Oku. (Translated via Generative AI)

Memory Does Not Always Rise to Consciousness

When we say we “remember” something, we tend to assume awareness is involved. But psychology draws a distinction: implicit memory refers to memory that operates without conscious recall. The classic example is a skill absorbed into the body — the way a musician’s fingers move without deliberate thought. Emotional and physiological responses can work the same way, replaying past experience without ever surfacing as conscious recollection.

Researcher Chiaki Ono, Professor Hiroaki Tomita, and their colleagues at Tohoku University Graduate School of Medicine, together with Associate Professor Tomohiro Uchida of Iwate University’s Faculty of Humanities and Social Sciences, set out to test whether this kind of memory also shapes the body’s response to media footage. Their findings were published in Frontiers in Psychiatry on May 11, 2026.

Freeze, Then Rebound

The study enrolled 36 healthy adults who had experienced strong shaking during the 2011 Great East Japan Earthquake but had not been directly affected by the tsunami. Participants watched four types of footage — natural scenery, earthquake footage, tsunami footage, and public service announcements broadcast repeatedly in the days after the disaster — while heart rate (HR) and heart rate variability (HRV) were continuously recorded before, during, and after each clip. HRV, which measures the fluctuation in time between heartbeats, is a well-established objective indicator of autonomic nervous system activity.

During disaster-related footage, heart rate and autonomic activity fell significantly compared to the neutral nature clips. The researchers interpret this as a “freeze” response — the momentary stillness that animals exhibit when facing a threat.

When the footage ended, the pattern reversed. Heart rate rose and sympathetic nervous system activity increased. From suppression during viewing to activation after it: this two-stage, time-delayed pattern was confirmed through objective measurement for the first time.

The Response No One Felt

The most striking finding involves the public service announcements. Unlike earthquake or tsunami footage, these clips contained no direct depictions of disaster. Yet the autonomic response followed the same pattern as the disaster footage. More tellingly, participants reported no significant change in subjective distress. Their bodies were responding to something their conscious minds did not register as upsetting.

The research group calls this “unconscious somatic memory” — the idea that repeated exposure to footage during the disaster period may have formed a kind of conditioned response, one that triggers autonomic reactions without any conscious involvement.

What “Unconscious Somatic Memory” Reveals

Memory comes in more than one form. There is the kind you can deliberately retrieve — what you had for lunch yesterday, a face you recognize — and the kind that simply acts, without being summoned. The latter is often called procedural memory: the body’s knowledge of how to ride a bicycle, how to play a chord. It surfaces not as recollection but as behavior.

What this study suggests is that memory of this involuntary kind can take root in emotionally charged experiences as well. Participants’ bodies responded automatically to footage they had seen before, even when they had no sense of “remembering” anything. The response was there; the awareness was not.

The body reacting without a felt sense of memory — that is not a gap in memory, but perhaps a different register of it entirely. Where exactly such traces are stored, and what form they take, remains an open question. This research illuminates one part of the answer, through the quiet evidence of a heartbeat.

Source: TOHOKU UNIVERSITY press release