A unique new imaging study compared brain activity of superagers learning novel information to youthful brains completing the same task. The results highlight exactly how some older adults can maintain good memory function, and directs researchers to brain regions that could be stimulated to enhance memory in aging adults.
Superagers are those elderly individuals who seem to maintain youthful cognitive functions well into their senior years. A few years ago, Alexandra Touroutoglou, from Massachusetts General Hospital (MGH), identified a local cohort of superagers with exceptional memory. Since then a team of MGH researchers has published several studies investigating what makes those superager brains different from regular elderly brains.
“Using MRI, we found that the structure of superagers’ brains and the connectivity of their neural networks more closely resemble the brains of young adults; superagers had avoided the brain atrophy typically seen in older adults,” says Touroutoglou of the team’s prior imaging findings.
The new study took a slightly different approach. Using functional magnetic resonance imaging (fMRI) the researchers looked at superager brain activity while they actively learned, and then recalled, new information.
Forty superagers were first presented a series of pictures paired with words. This “encoding” task allowed the researchers to track how the brain processes what it is seeing. Then, 10 minutes later, the participants were presented with more image-word pairs and tasked with identifying which pairs were new and which they had previously seen.
“In the visual cortex, there are populations of neurons that are selectively involved in processing different categories of images, such as faces, houses or scenes,” explains lead author Yuta Katsumi. “This selective function of each group of neurons makes them more efficient at processing what you see and creating a distinct memory of those images, which can then easily be retrieved.”
This mechanism is known as neural differentiation. Some collections of neurons specifically focus on faces, for example, while others may concentrate on identifying household objects. As we age, this mechanism diminishes in its specificity, meaning those specific neuron populations that previously only activated in response to one category of images now respond to other categories.
This particular decline in neural differentiation is hypothesized to be one of the factors underpinning age-related memory decline. Our neural activation patterns for specific scenarios become less distinctive, making it harder to recall memories.
A group of 41 young adults completed the same task and the researchers compared brain activity between the two cohorts. Focusing specifically on activity in the visual cortex, the researchers found the superagers showed youthful neural activity, particularly in the "fusiform gyrus and parahippocampal gyrus while viewing visual stimuli belonging to different categories." This brain activity was similar to what they were detecting in the 25-year-old cohort.
“The superagers had maintained the same high level of neural differentiation, or selectivity, as a young adult,” adds Katsumi. “Their brains enabled them to create distinct representations of the different categories of visual information so that they could accurately remember the image-word pairs.”
While these insights into superager brains are certainly fascinating they also offer researchers clues to ways we can improve cognitive functions in those of us who are just regular agers. The new study notes this particular cortical sensory processing mechanism is trainable so it is possible certain interventions could be deployed to help maintain neural differentiation and memory.
A clinical trial is also underway testing whether targeted noninvasive electromagnetic stimulation can activate certain parts of the brain and improve memory in older adults.
The new study was published in the journal Cerebral Cortex.
Source: MGH
