Putting the Mental in Sentimental

By Claire Tatham

Art by Ellie Yan

You open a box in your closet, and your old notebook falls out. The spiral binding is bent out of shape, and the sheets of paper are wrinkled from water damage, but the pages contain remnants of a past self. Each line is filled with doodles, secrets, and wishes that a younger you once had. Reading it over, you feel a twinge of . . . what is this feeling? Pain? Joy? Something in between? Perhaps the only proper label for this bittersweet emotion is “nostalgia,” or a sentimental longing and affection for the past [1].

Nostalgia comes from the Greek words “nostos,” meaning to return home, and “algos,” meaning pain [2]. This fittingly describes an almost inexplicable longing to return to a past time [3,4]. One of the first reported instances of nostalgia was during the 17th century, when people who enrolled in the army were reportedly not able to complete their duties because of the desire to return to their past lives [5]. Because of these effects, early physicians thought nostalgia was a mental disorder that was detrimental to peoples’ ability to function in daily life [6]. While this pathologization is outdated, nostalgia is still an extremely common experience, with one study finding that 79 percent of undergraduate students experience it at least once a week [4]. Nostalgia can also be a warm and comforting feeling, and studies have found that it can be conducive to increasing social connectedness and life satisfaction [3,7,8]. Nostalgia clearly plays a complex role in our lives, but how do our brains produce it? And why?

Since the sensation of nostalgia is closely linked to memory, having a foundational understanding of memory may be a helpful place to start exploring the mechanisms that give rise to this complex experience [9]. Current neuroscientific research classifies memory as either declarative or nondeclarative. While the declarative refers to facts or events that may be paired with emotions, the nondeclarative refers to skills and actions the body learns subconsciously [10]. As nostalgia is often triggered by memories that pertain to events in one's life, declarative memory will primarily be discussed in this article [11].

Declarative memories form via the neural mechanism of long-term potentiation (LTP) [10]. LTP refers to the process by which the junctions between neurons, known as synapses, are strengthened in the neural pathways that are repeatedly used within the brain [12]. Neurons carry information by propagating electricity through the cell [13]. At synapses, that information is carried from one cell to another via chemical messengers called neurotransmitters. Communication between neurons occurs so that information about the world’s stimuli can be passed throughout, and processed by, the brain. When a synapse is repeatedly activated, perhaps because a person is frequently exposed to said stimuli, certain neurons communicate repeatedly as a result [13]. Because of the repeated communication, the synaptic connection becomes stronger in order to make it easier for these neurons to communicate [14]. For example, when a person studies flashcards, the synapses in the brain that involve pairing the word and its definition grow stronger with repeated practice. This process of strengthening the connections between neurons through repeated activation is called LTP.

Strengthening the neural pathways that are active during memory formation allows those neurons to more easily communicate with each other later on, leading to memory recall. Because memories involve a wide variety of senses and associations, the brain regions where synapses strengthen for memory recollection vary from memory to memory [12,15,16,17]. For example, if a memory is related to the meaning of words, synapses involved in language processing may be strengthened when thinking of that memory [18]. However, there are some regions that are primarily associated with general memory formation. One such structure is the hippocampus, a region deep within the brain that is integral to learning and memory [19]. For example, one function of the hippocampus in memory appears to involve temporarily holding new facts about experiences before they are stored for long-term use [19].

However, declarative memories are not simply a matter of recalling facts. More often than not, they also involve a flurry of emotions that are associated with whatever is being recalled. As such, a declarative memory can also evoke intense emotion, in which case it is referred to as an emotional memory [11]. Emotional memories are highly associated with the amygdala, a small brain structure located near the hippocampus that is involved in a wide variety of functions [20]. In regards to emotional memory however, synapses in the amygdala can undergo LTP to strengthen pathways involved with strong emotions, such as fear or excitement. This form of LTP can help someone remember events that provoked these strong emotions [16,21,22]. Say our person from before didn’t flip their flashcards enough times before getting cold-called in class: LTP in the amygdala and hippocampus will work together to store the memory of that experience alongside the strong negative emotion that may be associated with it. After all, no one likes being caught unprepared—so your brain will make sure you remember for the next time!

Because intense feelings are brought up while recalling the past, nostalgia has many parallels to emotional memory. In fact, researchers have found the amygdala to be active when experiencing nostalgia much like it is with emotional memory [23]. However, being nostalgic is different from simply experiencing the same emotion that occurred at the time the memory was formed. Nostalgia involves an intense longing to return to the time of the memory, rather than simply recalling the sensations associated with it [3]. Physiologically, nostalgia may lead to increased body temperature, decreased heart rate, and increased blood oxygen level, suggesting that the body is relaxing in response to nostalgia [24-26]. So how does this unique longing occur during memory recall, instead of a simple recollection of past emotions?

One promising theory as to how nostalgia is generated involves the reward system alongside memory recall. In one study, researchers compiled a series of images, half of which were associated with a typical Japanese elementary school—such as those of typical childrens’ pencil cases and classroom bulletin boards—and the other half were comparable non-nostalgic images—such as purses or train station bulletin boards [9]. They had participants, who were raised in Japan with a similar elementary school upbringing, view the images while inside a functional magnetic resonance imaging (fMRI) machine, which measures neural activity in different regions of the brain using blood flow as a proxy. In this case, the researchers looked at brain areas involved in memory and reward systems. After the scans, the participants rated on a scale out of five how much nostalgia they felt each image evoked. The researchers then compared the measured brain activity during non-nostalgic and nostalgic image viewing. Specifically, they looked at coactivity—similar increases in activity between two regions—between regions of the brain involved in memory and those involved in reward. Coactivity between these regions would indicate a relationship in the amount of activity between these two separate pathways. They found that participants showed more coactivity between regions of the brain related to memory and areas related to rewarding experiences when looking at nostalgic imagery, as compared to when looking at non-nostalgic imagery. They interpreted this to mean that “nostalgia experiences involve both reward and memory systems” [9]. This involvement of the reward system alongside memories suggests a unique pattern of brain activity that contributes to nostalgia.

In fact, this study and many others led researchers Kikuchi and Noriuchi to propose a “nostalgia network” [27]. They suggest that this network works when a cue, such as an image of a childhood pencil case, induces older autobiographical memories instead of simply triggering areas that store information about the image. The recalling of these autobiographical memories is unexpected for the brain, perhaps because the person has not thought of the childhood pencil case in a long time. The brain likes these surprises and unexpected positive stimuli trigger the reward systems, meaning that this serendipitous recollection of autobiographical memory is processed in the brain in a manner similar to a reward. This coactivation of memory and reward systems is possibly the reason the brain generates the feeling of nostalgia we are all familiar with [27].

Motivation can be thought of as the desire and effort one puts in to obtain a reward. As such, this coactivation of the reward network with nostalgia would likely also affect motivation [28]. In fact, this is what researchers have found. Dijke et al. had workers recall a nostalgic memory before work everyday [29]. They found this increased the workers' intrinsic motivation and work effort compared to those who were asked to recall mundane life events daily [29]. Similarly, Sedikides et al. had participants list six of their personal goals in order from most to least important [30]. They then asked those participants to either reflect on a memory they knew would trigger nostalgia for them or an ordinary life event. After the participants recalled a memory or event, the researchers presented the goals back to the participants in a random order and had them rate their motivation to achieve those goals. They found that participants who recalled a nostalgic event had more motivation to achieve their most important goals than those that had remembered an ordinary event [30]. This finding could indicate that nostalgia may motivate us to do the things in life we value, like pursuing the passions that excite us, and spending time with the people we love.

Aside from motivation, nostalgia appears to serve as a coping mechanism. Several studies have found that nostalgia can be triggered during aversive situations such as moments of stress, facing death late in life, and even cold temperatures [4,25]. Not only can nostalgia be triggered during these situations, it has also been shown to improve a person's ability to cope with the situations themselves and improve emotions overall [31-33]. For example, Bohlmeijer et al. used a form of therapy for patients with depression called “life-review” which is based heavily on reminiscing about events in one's life [34]. They had the patients go through 2.5 hour sessions in which they were encouraged to reminisce about their life and express their feelings through various creative mediums. After undergoing the therapy for 12 sessions, the researchers found that one-third of the patients had a large reduction in depressive symptoms, based on two questionnaires [34]. In another study, Missel et al. analyzed patients’ descriptions of their own lives with incurable cancer and found that those whose narratives were more nostalgic experienced less existential anxiety [35]. While this research is less controlled and more observational than the other studies discussed, it nonetheless proposes that nostalgia can act as a soothing feeling in extremely challenging situations [35]. This is an optimistic conclusion as perhaps we can all use nostalgia to cope with our own lives.

Beyond the level of individual experience, a form of nostalgia has existed at the cultural and societal levels for hundreds of years. Romanticization of past eras can be seen in the Renaissance with the revival of Greco-Roman styles. Art during the Golden Age of India featured renewed styles created by the earlier Kushan empire, and today’s pop icons such as Bruno Mars and Janelle Monae use stylistic features from the 90s. Nostalgia is even used by companies and corporations to influence consumers [36]. One example of this phenomenon is Coca-Cola ads that utilize imagery from past decades, like the 40s or 50s, to tap into consumers’ desires to experience another time [36]. People may have associations with these times due to media that they have seen before, making them vicariously nostalgic for a time they never experienced. This idea has been explored by researchers; for example, Krumhansl and Zupnick did a study on college students in which they played music ranging from the 1960s, like the Beatles, to early 2000s, like the Black Eyed Peas [37]. They found that not only were college students nostalgic for music that came out during their childhood, but also for music that came out roughly 10 years before they were born. They hypothesized that, because the students’ parents were in their 20s when this music came out, the students had their own memories associated with that music because they heard it growing up [37]. Companies can utilize these memories and associations that young consumers have with a past time to evoke this vicarious nostalgia, and promote them as a way to buy the experience of a time they could never otherwise have.

Nostalgia is complex. It feels warm internally but can be triggered by aversive cold temperatures in the environment. It feels like a longing to return to the past, but it also motivates individuals to pursue what's important to them going forward. It’s something incredibly personal, but it can be used by large corporations on an industrial scale to advertise and promote consumerism. Nostalgia can be triggered by an unexpectedly broad range of stimuli, and you never know when that metaphorical notebook will fall into your lap. Embrace the uncertainty, and, when the feeling arises, let the warmth of nostalgia envelop you.