TOTAL RECALL: Memory is more than just the sum of the constituent features of an object or event, it is a so-called episodic packet that weaves together color, location and other features. Image: ¿ DAVID H. WELLS/CORBIS
People who are so-called simultagnosics have a problem with a crease in their brains that links the top and bottom of the parietal lobe. Because of damage to this crease, called the intraparietal sulcus, simultagnosics cannot actively perceive the different properties of an object. "If you don't have an actively functioning intraparietal sulcus and you are looking at a red car moving down the street, you can't actively perceive the color and the movement," explains neurobiologist Melina Uncapher of the University of California, Irvine. "You can only attend to the color or the movement." And now a new study led by Uncapher has revealed that this crease also plays a pivotal role in tying the separate strands of an event or object into a fully-woven memory.
Uncapher and her colleagues tested 20 volunteers on a variety of recall tests. While presented with a series of 100 words to remember, the subjects' brains were scanned with an fMRI machine. The researchers presented the fully capitalized words in one of four quadrants of a box on a small computer screen. The words were either in black or in one of four colors: red, green, blue or pink. For colored words, the subjects had to decide if a signified object was living or not, while for black-lettered words the test focused on whether the object would fit into a shoe box. "Location is automatically attended to, whereas color doesn't seem to be as attention-grabbing," Uncapher says. "If you throw in just a few words in black, then subjects have to attend to the color that they are seeing the words in."
Following the brain scan, the researchers tested the subjects' recall of the various words, their color and location, and then compared this with the subject's fMRI scans during the initial presentation. As expected, the various regions of the brain associated with determining color or location showed increased activity when subjects memorized either color or location specifically. But when they were in the act of memorizing all the features--uniting memory of the words, colors and locations--the intraparietal sulcus came into play. "When you are looking at the activity that is predictive of later memory, this region is selectively active," Uncapher notes. "If you are perceiving different elements as unified when first experiencing them, then you are more likely to remember them together."
Of course, memory is centrally mediated by the hippocampus, a region ensconced in the temporal lobe and therefore difficult to image. It did show some increase in activity in this test but only at a lower threshold, which Uncapher ascribes to the difficulty of distinguishing signal and noise from such embedded regions. And the research team did not scan the volunteers while they were committing the words to memory, according to the paper presenting the result in the November 9 issue of Neuron. "It would have been great to scan retrieval as well so we could look for similarities," she says. "That becomes a gigantic study, but that's in the works."
Nevertheless, the current research offers some compelling evidence that this obscure fold in the brain plays a critical role in enabling the storage of coherent, holistic memories. It also hints at what most students have always known. "If what you're putting in is a unified, integrated representation then that's more likely to be what you will get out," Uncapher adds. "You can't get something out of memory that you haven't put in. If you're not really attending to the location or the color of the object you're not going to remember it." Pay more attention next time, will you?