Decrements in heart rate variability during memory search.

Heart-rate variability (HRV) was recorded from subjects as they rested or performed two memory-search tasks with different memory-set sizes. Results indicated that all the estimates of HRV were considerably greater during resting periods than during the task but only the mid-frequency band (0.1 Hz component) reflected the changes in memory-set size by a more pronounced decrement with the higher load. Subjective mental-effort ratings collected for the task periods also reflected the different memory loadings but did not correlate with HRV measures.