Sliced. Image: Courtesy of Elizabeth Kensinger

A little over a decade ago, researchers began using functional magnetic resonance imaging (fMRI) to study the brain at the instant a memory is formed. Elizabeth Kensinger, an assistant professor in Boston College’s department of psychology, first started working with fMRI scans in 1998, as a graduate student at MIT.

The images presented here are from her ongoing research into how people remember emotional experiences, and how that process changes as people age. Her work is conducted at Massachusetts General Hospital and at her laboratory in McGuinn Hall.

The grouping of images above shows a series of MRIs—parallel “slices” from the bottom to the top of the brain (notice the eye sockets in the first few). Kensinger inputs the slices into a computer program that essentially stacks them atop one another, enabling her to see the brain as a 3-D representation or to re-slice it and examine it from another angle. Overlaid onto the slices above is color-coded data from an fMRI scan, showing spikes of brain function as the subject looks at a picture.

When neurons are activated, they call for oxygenated blood, which has different magnetic properties than non-oxygenated blood. An MRI, which works by passing a huge magnet over the area in question, is able to pick up this difference and thus pinpoint where neurons in the brain are firing at a particular moment.

3-D. Image: Courtesy of Elizabeth Kensinge

The 3-D image above is from an experiment in which Kensinger measured the brain activity of 20 young adults (ages 18–35) and 20 older adults (ages 64–80) while they were viewing a series of pictures designed to elicit a positive or negative emotional response—a smiling baby, say, or a snake about to strike. Later on, she showed the subjects the same pictures along with new ones to test whether they could correctly recall the images they’d seen. She then looked back at the initial brain data from the fMRI scans, to see which parts of the brain were most active when the subjects were processing the images they would end up remembering.

Kensinger and researchers elsewhere have found that older adults often show a “positivity shift in memory”—that as people age, they become better at remembering positive, or pleasurable, information than negative. The image at right, a frontal view of the brain, combines data from young and old subjects and highlights some of the processes behind that shift. The areas marked in red—most of them in the prefrontal cortex, where thinking about the meaning of information takes place—are activated as adults of all ages form pleasurable memories. The green areas are activated too—but only in older adults, signifying that older people engage additional areas of the brain to aid in remembering positive information. The green areas are all within the medial prefrontal cortex and cingulate gyrus, parts of the brain used to connect new information to prior experiences. And that, says Kensinger, raises some questions: “Do older adults link positive new information to their autobiographical experiences more often than young adults do, thereby creating a richer, more integrated, memory? And do they focus their attention more readily on positive information because they find it more rewarding than young adults do (because they can link it to past experiences), which then increases the likelihood that the information will be transformed into a stable memory?” Kensinger will continue her investigations as a 2008 Searle Scholar. The award supports independent research by young faculty in the biomedical sciences and chemistry.

Katie Bacon is a writer in the Boston area.