[Paleopsych] Live Science: Scientists Predict What You'll Think of Next

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Scientists Predict What You'll Think of Next
By Ker Than
LiveScience Staff Writer
posted: 22 December 2005
02:00 pm ET

[Joel Garreau's new book, _Radical Evolution: The Promise and Peril of 
Enhancing Our Minds, Our Bodies--and What It Means to be Human_ (NY: Doubleday, 
2005) has just arrived. I am signed up to review it for _The Journal of 
Evolution and Technology_ and commenced reading it at once. Accordingly, I have 
stopped grabbing articles to forward until I have written my review *and* have 
caught up on my reading, this last going on for how many ever weeks it takes. I 
have a backlog of articles to send and will exhaust them by the end of the 
year. After that, I have a big batch of journal articles I downloaded on my 
annual visit to the University of Virginia and will dole our conversions from 
PDF to TXT at the rate of one a day. I'll also participate in discussions and 
do up and occasional meme. But you'll be on your own in analyzing the news. I 
hope I have given you some of the tools to do so.]

To recall memories, your brain travels back in time via the ultimate Google 
search, according to a new study in which scientists found they can monitor the 
activity and actually predict what you'll think of next.

The work bolsters the validity of a longstanding hypothesis that the human 
brain takes itself back to the state it was in when a memory was first formed.

The psychologist Endel Tulving dubbed this process "mental time travel."

How it works

Researchers analyzed brain scans of people as the test subjects watched 
pictures on a computer screen. The images were divided into three categories: 
celebrities like Jack Nicholson and Halle Berry, places like the Taj Mahal and 
the Grand Canyon, and everyday objects like tweezers and a pocket mirror.

To make sure the subjects were paying attention, they were asked a question 
about each image as it came up, like whether they liked a certain celebrity, 
how much they wanted to visit a certain place or how often they used a certain 

Later, without any images and while their brains were still being scanned, the 
subjects were asked to recall as many of the images as they could.

The researchers found that the patterns of brain activity associated with each 
picture "reinstated" themselves seconds before the people could verbally recall 
the memories. On average, the time between beginning brain activity associated 
with the memory and the subjects verbally stating the memory was about 5.4 

"When you have an experience, that experience is represented as a pattern of 
cortical activity," explained Sean Polyn, a postdoctoral researcher at the 
University of Pennsylvania and leader of the study. "The memory system, which 
we think lives in the hippocampus, forms a sort of summary representation of 
everything that's going on in your cortex."

Googling your brain

The process can be compared to the way web crawlers work to browse and 
catalogue web pages on the Internet. Web crawlers are automated programs that 
create copies of all visited pages. Search engines like Google then tag and 
index the pages.

In the same way, as we're trying to remember something, our brains dredge up 
the memory by first recalling a piece of it, scientists say.

When trying to remember a face you saw recently, for example, you might first 
think broadly about faces and then narrow your search from there, enlisting new 
details as you go, Polyn explained. It's like adding more and more specific 
keywords to a Google search, until finally you find what you want.

Scientists call this process "contextual reinstatement."

"The memories that came up would be hits and the ones that most match your 
queries would be the ones that came up first," Polyn told LiveScience.

Reading your mind

The researchers were even able to do a little mind-reading by watching the 
search in progress.

By comparing the brain scans of the subjects while they tried to remember the 
images they'd seen with those collected when they first viewed the images, the 
researchers were able to correctly conclude whether the people were going to 
remember a celebrity, place or object.

"We can see some evidence of what category the subject is trying to recall 
before they even say anything, so we think we're visualizing the search process 
itself," Polyn said.

A similar mind-reading effort was announced earlier this year, when researchers 
found they could predict where a patient would move his hand based on brain 
activity the instant prior.

Scientists think that contextual reinstatement is unique to memories that 
involve personal experiences, so-called "episodic" memories, but that similar 
processes might be at work in other forms of memory.

The study was detailed in the Dec. 23 issue of the journal Science.

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