Influence of acute exercise on association memory for emotional and neutral pictures

• Author / Creator

  Olafson, Danielle

• Introduction: The beneficial effects of chronic exercise on hippocampal volume and associated memory functions are well studied, especially in the context of aging and dementia. These effects are thought to be mediated by multiple exercise-induced physiological and molecular factors (e.g., cortisol, BDNF, neurotransmitters), which directly or indirectly influence hippocampal structure and function. However, whether an acute bout of exercise can influence memory functions is less clear. In humans, association memory, i.e., relational memory for two or more items has been associated with hippocampal function, and some studies have examined how acute exercise may affect associative memory performance. Acute exercise also influences mood, but effects on emotional types of memory are sparse and equivocal. In the current study, we used an association memory task with emotional and neutral picture pairs, previously shown to engage the hippocampus, and to produce an emotional memory bias favoring neutral pairs of images over emotional (negative, high-arousing) pairs. The purpose of the current study was to test whether differing intensities of exercise change emotional association memory performance in this task.
  Hypotheses: We tested two alternative hypotheses. Compared to low-intensity exercise and no-activity controls: 1) High intensity exercise will nullify arousal effects of the emotional materials on memory and decrease the typical memory bias for neutral picture pairs. 2) High intensity exercise will intensify the typical memory bias, creating an even larger memory advantage for neutral pairs. In addition, based on previous non-emotional association memory studies, we predicted: 3) High intensity exercise will increase overall association memory regardless of emotional valence of the pictures.
  
  Methods: In a pseudorandomized blinded experiment, 95 undergraduate students were assigned to one of three experimental groups: A high intensity group in which participants cycled to 90% of their maximum heart rate (n=31), a low intensity group which leisurely cycled to no more than 50% of their maximum heart rate (n=33), and a no-activity control group watching a nature video (n=31). Heart rate was continuously monitored to measure physiological reactivity. The memory task (from Madan et al., 2017) contained negative and neutral picture pairs, tested association memory through associative recognition, and was conducted before and after the intervention.
  Results: Results indicated that the exercise intervention was successful. Both the low and high intensity groups had the same resting heart rate, but the high-intensity group demonstrated more pronounced heart rate changes compared to the low intensity group throughout the intervention. Average association memory performance, differential memory for neutral versus emotional pairs, and subjective memory performance were indistinguishable between groups, with clear evidence for null findings based on Bayesian statistics, although the high intensity group showed atypical memory performance already prior to the intervention. Within the high intensity group, participants who had a greater physiological response to the intervention demonstrated better memory both before and after the intervention than individuals with a weaker response. Discussion and conclusion: Based on these outcomes, acute exercise seems ineffective to change performance in emotional association memory, with Bayes factors conclusively suggesting null-findings. Nevertheless, outcomes could also be linked to a variety of experimental factors including high variability of the memory bias across participants, recruitment/sampling, test duration, and other uncontrolled factors (dispositional fitness levels, recent real-life exercise, time of day). The relationship between the responsiveness to high intensity exercise and memory mirrors similar findings in previous literature, indicating that responsiveness to higher intensities of exercise is related to better memory. This suggests that participants who are physiologically more responsive (higher heart rate) to high intensity exercise may have better memory performance regardless of acute exercise. In conclusion, future studies with healthy, young participants may focus on non-emotional association memory tasks with a shorter duration and may benefit from more intensive investigation of participant fitness levels as well as additional heart rate measures (e.g., variability, fluctuations) in order to ascertain whether exercise-based association memory changes are restricted to individuals with a stronger response to exercise.

• Subjects / Keywords

  • episodic
  • emotional
  • association
  • exercise
  • declarative
  • acute
  • memory
  • fitness
  • emotion

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-r0cm-xt26

• License

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