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Memory and reward systems coproduce 'nostalgic' experiences in the brain - PubMed

Memory and reward systems coproduce 'nostalgic' experiences in the brain

Kentaro Oba et al. Soc Cogn Affect Neurosci. 2016 Jul.

Abstract

People sometimes experience an emotional state known as 'nostalgia', which involves experiencing predominantly positive emotions while remembering autobiographical events. Nostalgia is thought to play an important role in psychological resilience. Previous neuroimaging studies have shown involvement of memory and reward systems in such experiences. However, it remains unclear how these two systems are collaboratively involved with nostalgia experiences. Here, we conducted a functional magnetic resonance imaging study of healthy females to investigate the relationship between memory-reward co-activation and nostalgia, using childhood-related visual stimuli. Moreover, we examined the factors constituting nostalgia and their neural correlates. We confirmed the presence of nostalgia-related activity in both memory and reward systems, including the hippocampus (HPC), substantia nigra/ventral tegmental area (SN/VTA), and ventral striatum (VS). We also found significant HPC-VS co-activation, with its strength correlating with individual 'nostalgia tendencies'. Factor analyses showed that two dimensions underlie nostalgia: emotional and personal significance and chronological remoteness, with the former correlating with caudal SN/VTA and left anterior HPC activity, and the latter correlating with rostral SN/VTA activity. These findings demonstrate the cooperative activity of memory and reward systems, where each system has a specific role in the construction of the factors that underlie the experience of nostalgia.

Keywords: autobiographical memory; fMRI; nostalgia; resilience; reward.

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Figures

Fig. 1.
Fig. 1.

Examples of experimental stimuli. The upper row shows nostalgic pictures and the lower row shows control pictures (left column: object pictures, right column: scene pictures). All pictures were given a short title in order to ensure visual recognition and facilitate memory access (written in Japanese). Note that both nostalgia and control pictures were emotionally neutral, and were matched on their visual features such as content and angle.

Fig. 2.
Fig. 2.

ROI analyses of brain activity for nostalgia vs control events. (A) The eight ROI masks used in this study. The four hippocampus ROIs [L.aHPC (red), L.pHPC (cyan), R.aHPC (blue) and R.pHPC (orange)] were created by dividing the AAL HPC masks into anterior and posterior portions (y = −21 mm, MNI coordinates), and four reward-related ROIs [SN/VTA (yellow), L.VS (purple), R.VS (green) and VMPFC (brown)] were created using coordinates reported in a meta-analysis concerning reward processing (for more details, see the Region of interest analysis section). (B) HPC and reward-related ROIs that showed significant activity differences between the nostalgia and control conditions. The mean parameter estimates (beta values) for each ROI were extracted from each condition and compared using paired t-tests (P < 0.05, FWE corrected by Holm method). Error bars show individual differences (SEM). Asterisks (*) denote a significant difference between conditions. (C) Among the HPC and reward-related ROIs, the L.aHPC and R.VS were co-activated and the L.aHPC-R.VS co-activation index was significantly correlated with nostalgia tendency (r (12) = 0.63, P = 0.047). The co-activation index was defined as the first eigenvalue of these two ROIs’ activity (parameter estimates) that represents co-activation strength. Nostalgia tendency was defined as the individual mean nostalgia score across all experimental stimuli in this study (52 pictures). L, left; R, right; aHPC, anterior hippocampus; pHPC, posterior hippocampus; FWE, family wise error.

Fig. 3.
Fig. 3.

Neural activation correlated with two different aspects of nostalgia. Emotional and personal significance (factor 1) was correlated with activation of the caudal portions of the SN/VTA and L.aHPC (shown in red), whereas Chronological remoteness (factor 2) was correlated with activation of the rostral SN/VTA (shown in yellow). aHPC, anterior hippocampus.

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