Imaging Data Suggest Why Some Memories Remain Vivid, Even in AD

It is well documented that people remember better when their memories are enhanced by emotions. For instance, most people recall special days in their lives such as their graduation or wedding, and most American adults recall where they were on September 11, 2001. Such emotionally charged memories are often referred to as “flashbulb memories.”

Even individuals with Alzheimer’s disease (AD) seem to recall better when their memories are tinged by emotions than when they are not. However, this does not seem to be the case for individuals with frontotemporal dementia (FTD).

These findings appeared in the October 10 Brain. The senior researcher was Olivier Piguet, Ph.D., an associate professor at Neuroscience Research Australia.

The cohort included 59 subjects—10 with AD, 34 with FTD, and 15 healthy controls. All three groups were matched for age, gender, and education. The subjects were shown 40 emotionally charged pictures and 40 emotionally neutral pictures and were again shown the photos an hour later or so to see whether they recognized them. Both the AD subjects and the control subjects recognized the emotionally charged pictures significantly better than the nonemotionally charged ones. However, the FTD subjects recognized both with the same degree of frequency.

Thus it looks as if individuals with AD, but not with FTD, have some access to emotionally charged memories. And if so, it has implications for the management of both types of patients, the researchers believe.

For example, since Alzheimer’s patients have some access to emotionally charged memories, showing them photos from their past or playing music from their past might help them remember their past better. Or as the researchers said in their report, “We have demonstrated that despite their memory deficits…emotion exerts a significant effect on memory performance in Alzheimer’s disease…. [These findings suggest] that at an early stage in the disease course, patients with Alzheimer’s disease can harness emotional aspects of stimuli to facilitate subsequent retrieval.”

In contrast, since FTD patients do not have access to emotionally charged memories, it might help the family members of FTD patients to understand why the patients are often apathetic and disengaged from social and family events. “It is possible that this social withdrawal may arise, in part, from a failure to recollect past events, particularly the emotional aspects of such experiences,” they suggested.

The study also included a brain-imaging component. The researchers used a structural MRI scanner to make brain scans of the subjects. They then used a software package called voxel-based-morphometry to analyze the MRI data and to see whether there were any correlations between subjects’ memory test results and gray-matter intensity in various areas of their brains.

They found that such correlations did exist. Voxel-based-morphometry analyses confirmed that whether subjects had AD or FTD, or were healthy controls, overall memory performance was associated with a distinct set of brain regions that included the left hippocampus, posterior cingulate, precuneous, right superior and middle temporal gyri, and postcentral gyrus—regions classically associated with episodic memory performance. In contrast, emotional enhancement of memory was associated with a separate set of frontal-lobe structures, which included the right orbitofrontal and subcallosal cortex, the right frontal operculum cortex, and the inferior and middle frontal gyri, with the largest cluster present in the right orbitofrontal cortex.

“These results,” they said, “provide strong evidence for the specialization of distinct frontal and temporal lobe regions for overall memory and emotional enhancement of memory,” and not just in healthy individuals, but in those with AD or FTD. “In contrast with overall memory, memory for emotional stimuli involved different brain regions and was associated with the orbitofrontal cortex predominantly. The orbitofrontal cortex shares strong bidirectional connections with the hippocampus and amygdala…. Our neuroimaging results therefore suggest that the integrity of the amygdala alone is not sufficient for the emotional enhancement of memory effect to occur.”

Moreover, these findings may help explain why FTD patients do poorly at emotionally charged remembering. The major brain part that reacts emotionally to stimuli—the orbitofrontal cortex— is probably damaged by their dementia.

The study was funded by the Australian Research Council. ■

An abstract of “The Orbitofrontal Cortex Is Involved in Emotional Enhancement of Memory: Evidence From the Dementias” is posted at http://brain.oxfordjournals.org/content/136/10/2992.abstract.