Researchers led by William Kelley of the department of psychological and brain sciences at Dartmouth College recently discovered that individual differences in memory ability in healthy young adults may be predicted by medial temporal lobe (MTL) blood-oxygen-level-dependent (BOLD) activity at rest. The finding was published this month in PNAS.

To better understand why human beings differ in their ability to form and retrieve long-term memories, Kelley’s team used functional magnetic resonance imaging (fMRI) to measure BOLD activity in 50 healthy young adults during alternative periods of resting fixation and simple cognitive tasks.

During scanning, two experiments were performed, and data were collected in a single scanning session. In the first experiment, subjects engaged in long periods of a simple judgment task that alternated with periods of rest, during which subjects simply fixated on a crosshair.

In the second experiment, all 50 subjects were scanned using an event-related design in order to determine whether any relationship between resting MTL activity and memory would generalize to more rapid transitions between task and rest. The event task trials during the second experiment required subjects to respond with a button press at both the onset and offset of a flickering black-and-white checkerboard.

After scanning, subjects completed cognitive tests to provide psychometric measures of general intelligence, vocabulary and long-term memory ability across various domains.

The researchers found that individuals who demonstrated superior memory during testing also exhibited greater magnitudes of task-induced deactivations in MTL BOLD signal during rest. Task-induced deactivation refers to a certain regional decrease in BOLD signal during a cognitive task compared to a baseline.

The relationship is independent of differences in general cognitive function and proved consistent across variable resting period durations, control tasks (number of judgment versus checkerboard detection) and experimental designs (blocked versus event related). This relationship is present in a region known to be critical to the formation and retrieval of long-term memories.

Further, the fact that the resting-state MTL functional connectivity is reduced in patients with Alzheimer’s disease led Kelley’s team to hypothesize that individuals demonstrating significantly reduced levels of MTL resting period activity may be those that are more susceptible to ensuing mnemonic impairment, and that this predisposition may be directly related to the genetic make-up of individuals.

According to the article, the team proposes that “resting-state MTL activity should be explored as a potentially viable biomarker for early detection of ensuing neurological and mnemonic degeneration, possibly permitting early intervention strategies aimed at both improving memory function and forestalling age-related memory decline.”