Investigating fractal dimension, heart rate variability, and memory during different image sequencing regimes in young adults.

The goal of this study is to investigate patterns that emerge in brain and heart signals in response to external stimulating image regimes. Data were collected from 84 subjects of ages 18-22. Subjects viewed a series of both neutrally and negatively arousing pictures during 2-min and 18-s-long segments repeated nine times. Both brain [electroencephalogram (EEG)] and heart signals [electrocardiogram (EKG)] were recorded for the duration of the study (ranging from 1.5 to 2.5 h) and analyzed using nonlinear techniques. Specifically, the fractal dimension was computed from the EEG to determine how this voltage trace is related to the image sequencing. Our results showed that subjects visually stimulated by a series of mixed images (a randomized set of neutrally or negatively arousing images) had a significantly higher fractal dimension compared to subjects visually triggered by pure images (an organized set of either all neutral or all negatively arousing images). In addition, our results showed that subjects who performed better on memory recall had a higher fractal dimension computed from the EEG. Analysis of EKG also showed greater heart rate variability in subjects who viewed a series of mixed images compared to subjects visually triggered by pure images. Overall, our results show that the healthy brain and heart are responsive to environmental stimuli that promote adaptability, flexibility, and agility.

Contributions of Arousal, Attention, Distinctiveness, and Semantic Relatedness to Enhanced Emotional Memory: An Event-Related Potential and Electrocardiogram Study.

Enhanced emotional memory (EEM) describes memory benefits for emotional items, traditionally attributed to impacts of arousal at encoding; however, attention, semantic relatedness, and distinctiveness likely also contribute in various ways. The current study manipulated arousal, semantic relatedness, and distinctiveness while recording changes in event-related potentials and heart rate during memory encoding. Trials were classified as remembered or forgotten by immediate recall performance. Negative images were remembered significantly better than neutral, and related neutral images were remembered significantly better than unrelated neutral images. Higher P300 and late positive potential (LPP) amplitudes were associated with memory for negative images as compared with related neutral images, suggesting that negative images received additional attentional processing at encoding, and that this cannot be accounted for only by the inherent relatedness of negative stimuli. No encoding benefits were found for related neutral images though they were better remembered than unrelated neutral images, indicating retrieval dynamics impacted memory. When image types were intermixed, greater heart rate changes occurred, and negative and unrelated neutral images received increased elaborative processing as compared with related neutral images, perhaps due to the prioritization of encoding resources. These results suggest encoding and retrieval processes contribute to EEM, with emotional items benefiting additively.