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Amnesia and sad films
The patients had damage to the medial temporal lobe and hippocampus, which left them with severe anterograde amnesia. Leave the room for five minutes and come back, and they stand up to shake your hand and introduce themselves as if you had never met. Researchers at the University of Iowa showed them and a group of healthy controls some very sad movie clips. The patients followed the clips, got weepy, and rated themselves as very sad, just like the controls.
Sadness without memory
Five minutes later, the controls still felt a little sad, and they could say why: they remembered the movie. The patients still felt really sad too. Asked how they felt, they said they felt really sad and had no idea why. Asked if they remembered seeing a movie, they answered no. There was no declarative memory of the movie at all, and the sadness lasted anyway.
An emotional state keeps running on its own clock, apart from the memory of what set it off. Sadness probably has one of the longest time constants of any emotion. A reflex has no such lingering, because it runs straight through and is gone.
Why can amnesia patients still feel emotions?
The hippocampus and nearby medial temporal structures are needed to form new declarative memories, but they are not where emotional states are generated. Emotion draws on other circuits, including the amygdala, hypothalamus, and brainstem, which stay intact in many amnesia patients. The best-known amnesia patient, Henry Molaison, lost much of both medial temporal lobes in a 1953 operation by surgeon William Scoville. Psychologist Brenda Milner then showed that he could still learn motor skills such as mirror drawing without remembering the practice sessions.
How can a mood outlast its cause?
Many mood-related signals are carried by neuromodulators such as noradrenaline, serotonin, and dopamine, which are released diffusely and act over seconds to hours rather than milliseconds. Stress hormones are slower still, since cortisol released into the blood takes tens of minutes to clear. Neither system depends on remembering what set it off. Together they let a body stay in a state long after the triggering event has dropped out of mind.
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