Understanding the Nostalgic Brain

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When my youngest child went off to college several years ago, leaving my wife and me alone in our house for the first time in 24 years, I found myself in the grips of an intense and prolonged bout with nostalgia. Every time I left home to go to work or run an errand, I’d pass a baseball field, ballet studio, or park that played some role in one of our children’s lives and suddenly be overwhelmed with a powerful wave of bittersweet pleasure that simultaneously warmed my heart and stung my eyes. So intense and complex were the emotions coursing through my body during these daily encounters with the past that they set me on a quest to find out what exactly was going on in my brain to make me feel that way.

My initial search turned up a number of interesting studies from the field of psychology, where a handful of researchers had been studying nostalgia for the better part of two decades, but the field of neuroscience—which I looked to for answers about the chemical and biological processes responsible for the emotions that the psychologists had been studying—had very little to say about the subject. Since that time, however, neuroscientists have joined the psychologists and conducted several studies aimed at answering the question I first asked when my daughter left home for college—namely, what is going on in our brains when we’re feeling nostalgic. A prospective review recently published in Social Cognitive and Affective Neuroscience synthesizes this body of research into a “neural model of nostalgia.”

A complex emotion

Even without doing any formal research on the subject, most of us would characterize nostalgia as a multifaceted emotion involving many different components (as evidenced, for example, by the common use of the oxymoron “bittersweet” to describe it). Starting with the multifaceted nature of nostalgia as a premise, the writers of the article identify four distinct components that work together to generate the emotion that we label “nostalgia,” describe the role that each of these elements plays in nostalgic experience, identify brain regions involved in these components, and then review several neural studies of nostalgia to determine if these regions are, in fact, involved in nostalgia, and how they work together to create a nostalgic experience. The four components identified by the writers as playing a role in nostalgia are self-reflection, autobiographical memory, emotion regulation, and reward.

Self-reflection

With the self being “the central and defining character of nostalgia,” self-reflection is obviously an integral part of the nostalgic experience. We are, after all, the leading actors in the memories that we classify as nostalgic, so some reflection on the type of role we play in those memories is necessary for determining how important or meaningful those past experiences are to the present circumstances in which we remember them.

The self-reflection processing involved in linking our past with our present in a way that generates nostalgia “requires integrating stimuli in the context of personal thoughts, goals, and traits.” Two brain regions previously identified as being crucial to self-reflection processing are the medial prefrontal cortex (mPFC) and the posterior cingulate cortex (PCC). Both the mPFC and the PCC “show heightened activation when individuals reflect on the information that is highly self-relevant and self-self-descriptive.”

Autobiographical memory

Autobiographical memory, which involves the processing of our past self through mental time travel, provides the content of our nostalgic experiences. Since our reflection on past experiences can be negative as well as positive, including rumination and counterfactual thinking (a “what if” approach to some remembered experience we wish had turned out differently), nostalgic recollection “can be considered a special case of autobiographical memory,” contrasting with these other forms of autobiographical memory in its predominantly positive associations. Brain regions that have been previously identified as being involved in autobiographical memory processing are the mPFC and the PCC (which also play a key role in self-reflection), and the hippocampus.

Emotion regulation

In addition to its generally positive content, nostalgia also differs from general autobiographical memory in its distinctively complex emotional character. While a predominantly positive emotional experience, nostalgia has a distinctive “affective signature” in that it is ambivalent, involving “the co-occurrence of positive and negative affect” (hence the common “bittersweet” designation of nostalgia). The ambivalent nature of nostalgia allows it to play a role in emotion regulation.

Ambivalent emotions “entail neural mechanisms both of simultaneously positive and negative states and a rapid vacillation between positive and negative states.” As such an ambivalent emotion, nostalgia regulates negative states and soothes emotional conflict. Brain regions that have been identified as playing a role in emotion regulation include the mPFC (once again) and the anterior cingulate cortex (ACC).

Reward

Satisfying stimuli are known to activate reward-related brain regions, and the predominantly positive emotions associated with nostalgia certainly qualify it as a satisfying stimulus. Numerous studies have also shown nostalgia to be related to motivation and reward seeking. It is likely, then, that nostalgia involves brain regions associated with reward processing. Brain structures identified as being part of the reward network include the striatum, the substantia nigra, the ventral tegmental area, and the ventromedial prefrontal cortex.

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Four components work together to produce nostalgia.

To determine how closely the brain regions associated with the four components they identified match those involved in nostalgia, the writers of the article reviewed six neuroscientific studies that directly addressed the neural bases of nostalgia and several other studies that did not address nostalgia directly but were highly relevant to it. Their review of the literature largely confirmed their hypothesis, showing that “nostalgia involves brains structures known to be engaged in self-reflection (mPFC, PCC and precuneus), autobiographical memory (hippocampus, mPFC, PCC and precuneus), emotion regulation (ACC and mPFC) and reward processing (SN, VTA, STA, and vmPFC).” Just as importantly, the review also provided some insight into how these regions work together to produce our subjective experience of nostalgia.

In one fMRI study, for example, participants viewed pictures of objects and scenes associated with childhood, along with more contemporary pictures, and were asked to rate the memory and emotion they experienced in response to the pictures. The pictures rated as nostalgic elicited stronger activity in the hippocampus, which is involved with autobiographical memory, and the ventral striatum, which is part of the brain’s reward system. Hippocampus-VS coactivation under the influence of experimentally produced nostalgia suggests that the brain’s memory and reward systems work together to “coproduce” the nostalgic experience.

Of particular note in the literature review was the prevalence of the medial prefrontal cortex in the nostalgia studies. Given its role in processing self-relevant information, autobiographical memory, and self-conscious emotion, the writers speculate that “the mPFC may serve as a hub that links self-reflection processing with autobiographical memories and emotions and plays an integrative role in the experience of nostalgia.”

Applications

The writers’ observation that the components comprising nostalgia and the brain systems with which they are associated are “interdependent and coordinated” may help to explain the numerous psychological benefits which psychologists have identified as being offered by nostalgia. Furthermore, the understanding of how nostalgia influences neural activity within multiple brain structures opens the door to possible nostalgia-based therapies for emotional and memory dysfunctions. The writers acknowledge that a great deal more research is necessary before such therapies can become a reality but hope that the neural model of nostalgia they propose “provides a good starting point for unraveling the neural basis of nostalgia.”