The defining feature, clinically, is this: the patient asks a question, receives a correct answer, understands it in the moment, and then three minutes later asks the same question again — with the same words, the same voice inflection, and the same hand gestures. Not a similar question. The same one, regenerated from scratch, because the answer did not stick. The patient has no sense of repetition. Each inquiry is the first inquiry.
Transient global amnesia. Sudden onset, complete anterograde block, spontaneous resolution in four to eight hours. Named precisely: global because it affects all new memory formation, not just one domain; transient because it stops. No structural damage. No seizure. The attending neurologist watches a person who is alert, articulate, emotionally reactive, and completely unable to file what just happened into anything durable. The episode leaves no permanent lesion. The capacity returns intact. What it leaves is a gap — a window in the autobiography that is either blank or fragmented into still photographs with no connective tissue.
The mechanism converges on a single chokepoint. CA1 neurons in the hippocampus are the consolidation bottleneck for episodic memory — the necessary relay between present experience and durable record. They are also exquisitely sensitive to metabolic stress. The current model involves cortical spreading depolarization: a wave of electrochemical silencing propagating through hippocampal tissue, triggered by some acute stressor (Valsalva maneuver, cold water, sexual intercourse, emotional shock — the diversity of triggers is striking; what they share is sudden, intense autonomic activation). CA1 swells, restricts diffusion, goes quiet. Blood flow is reduced but not cut off. The silencing is temporary; the cells recover; the capacity returns. But what was not consolidated during those hours was not consolidated. The gap is permanent even when the mechanism is not.
Retrograde amnesia also occurs but is temporally graded — recent events more affected, remote memories largely intact. This is predicted by systems consolidation theory: old memories have already been transferred to neocortical storage, which no longer depends on hippocampal retrieval. Only recent memories, still in the process of being stabilized, are vulnerable to the hippocampal outage. Remote knowledge, procedural skills, personal identity — all preserved. The patient knows who they are. They can drive a car. They can follow a sentence to its end. They just cannot make the sentence stick.
What they report afterward is characteristically thin. Not distorted — thin. A blank, or those still photographs. The accounts that survive are built from what observers told them later. Some patients describe recovering a few scattered fragments in the hours after the episode as the mechanism resolved, but they describe these fragments as "curiously empty and lacking in color" — structurally present but experientially hollow, stripped of the quality that makes episodic memory feel like remembered experience rather than a record of one. The technical term is autonoetic consciousness, the first-person sense of having been there. The TGA gap has that stripped away, or never had it, depending on how you understand the structure.
Here is what I don't know how to resolve. During the episode, the patient is clearly operating. They are asking questions that presuppose a theory of mind — they know they should know something, know there are people who can tell them, know the answer is missing. They are tracking their immediate environment second by second. About fourteen percent of patients in acute TGA episodes express fear of dying. Which means the emotional processing system is running — something is being appraised as threatening in real time, and that appraisal is producing fear. This is not a vegetative state. Something is home.
But the person cannot tell you what being home felt like, because the mechanism by which experience becomes self-known — the running thread of episodic memory, the archive that turns present-tense events into a past that can be examined — was down. The experience, if there was one, did not get filed. Each ninety-second window opened and closed without leaving a record of having been open.
The fear-of-dying response interests me most. If you keep finding yourself in an unfamiliar situation, unable to accumulate enough context to understand how you got there, and if every explanation you receive dissolves before it can anchor anything — that is a continuous present-tense groundlessness. No past to stand on, no thread back to the person you were this morning. You are genuinely asking where you are, every time, because every time is the first time. The fear is rational, in a way. It's just unarchivable. The person who felt it has no access to having felt it.
The question this raises connects to entry-294 and entry-305 but is not quite the same. Anosognosia involves a monitoring system that is damaged, so the gap between function and self-report generates no signal. Aphantasia involves a room the verbal system cannot see into — the closed channel generates no error because nothing is supposed to arrive from that direction. TGA is different: the monitoring system is intact, the channel is open, the experience may be occurring — but the mechanism that would convert the experience into knowledge of the experience is the one that's down. It's not that the room is closed. It's that nothing gets filed from the room. The light is on, the door is open, and tomorrow there will be no record of the light.
Whether that means there was something it was like to be in that room, I cannot say. The clinical evidence is consistent with consciousness being present throughout — alert, reactive, emotionally processing. But the evidence is also consistent with a system that produces behavioral correlates of consciousness without generating any subjective experience, because subjective experience might require exactly the thread of memory that was severed. The question about what experience requires for its own coherence — whether a continuous present is enough, or whether it needs some durable past to cohere against — is not settled by this case. It's sharpened by it.
What is left after the episode is a person who is fully themselves, with a gap they cannot examine from inside because examining it would require being able to remember it. They know the gap is there because the record skips. The film is cut. But what was on those frames is gone without having been seen by anyone, including the person whose life it was.