Memory In Action

  • Posted 06.01.09
  • NOVA scienceNOW

A remarkable experiment confirms what brain scientists have long suspected: Each experience that we have involves a particular group of neurons firing together. And when that experience is recalled, the same neurons spring to life.

Running Time: 03:07


Memory in Action

Posted: June 1, 2009

CHAD COHEN: More than 50 years after H.M.'s operation one scientist can actually get inside a living human brain and watch, even listen, as memories form.

ITZHAK FRIED: So what you can see here is a tiny neuron in the brain responding, and you can hear it, like [imitates noise], you hear it? [Imitates noise].

CHAD COHEN: These firing neurons were detected by ultra-thin electrodes placed in the hippocampus of epileptic patients like Mary. The electrodes can pinpoint where her seizures are occurring so that malfunctioning brain cells can be surgically removed. In the meantime Mary is offering her doctor a rare opportunity to observe her brain as it creates and recalls memories. First she watches a series of video clips, then hours later she recalls the clips at random.

ITZHAK FRIED: You just ask the patient to bring a memory supposedly out of nowhere, right, because they're not seeing anything. They are in their own mind searching for an experience.

CHAD COHEN: After a successful surgery, Fried shows Mary how a single neuron captures and recalls a memory.

ITZHAK FRIED: This is a neuron actually firing.

MARY: Really?

ITZHAK FRIED: Yeah, so now it's kind of firing a little bit here and there, it's not really excited, okay? Now look what happens here.

MARY: [Laughs]

ITZHAK FRIED: You hear what happens here? And what you have here is that neuron, that tiny neuron out of hundreds and hundreds of millions of neurons, just got really excited about this. And now comes the memory part, right? Nothing is being shown, and only memory is working, right? And the same neuron we've seen before, when the memory comes into mind.

RECORDED VOICE: Hollywood sign.

ITZHAK FRIED: Hollywood sign. The neuron is not excited. And now we're approaching –

MARY: The Simpsons.

ITZHAK FRIED: Okay. Now look, look.

MARY: [Laughs] I was right.

ITZHAK FRIED: So you were right, absolutely. And just before the Simpsons comes into mind, that cell starts firing.

MARY: Yeah, exactly.

CHAD COHEN: The experiments confirm what scientists have long suspected. An experience is a particular group of neurons firing together. And when that experience is recalled, the same neurons spring to life.

ITZHAK FRIED: This is really memory in action. We're not catching the entire metric, obviously. We're just having a little glimpse. It's a window into the brain.


Produced for NOVA scienceNOW by
Sarah Holt.
© WGBH Educational Foundation

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