Control over memory retrieval is predicted by heart rate variability.

Here is a fascinating observation from Gillie et al., who find that a physiological marker, heart rate variability, correlates with a person's ability to control unwanted memories. They use a think/no-think (TNT) task to demonstrate this:

In the TNT paradigm, participants learn a list of cue-response word pairs (e.g., “Tape-Radio”). They are then repeatedly presented with the cues studied earlier (e.g., “Tape”). In the think trials, they are asked to think of the response word (e.g., “Radio”). In the no-think trials, they are asked to prevent recall of the response word. Thus, in the latter case, participants attempt to intentionally stop the retrieval of a memory when presented with a cue. Successful suppression of a target memory should reduce its accessibility at a later point; therefore, recall for the response words is assessed at the end of the experiment. A recent meta-analysis of studies in which this paradigm has been used showed that, on average, people tend to have significantly lower recall of no-think items than of baseline items (word pairs that were studied in the initial phase but not presented in the experimental phase; Levy & Anderson, 2008). This finding, known as the negative-control effect, is taken to be evidence that people can successfully inhibit retrieval of an unwanted memory and that doing so impairs recall for that particular memory.

Here is their abstract:

Stopping retrieval of unwanted memories has been characterized as a process that requires inhibition. However, little research has examined the relationship between control over memory retrieval and individual differences in inhibitory control. Higher levels of resting heart rate variability (HRV) are associated with greater inhibitory control, as indicated by better performance on a number of cognitive, affective, and motor tasks. Therefore, we tested the hypothesis that higher levels of resting HRV predict enhanced memory inhibition as indexed by performance on the think/no-think task. Efforts to suppress no-think word pairs resulted in impaired recall for those items, as in past studies. Moreover, higher levels of resting HRV were associated with more successful suppression, as indicated by lower recall of the to-be-avoided stimuli relative to baseline stimuli. These findings are among the first to suggest that physiological markers of inhibitory control can be used to index a person’s capacity to control unwanted memories.