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During the day, Paris is a bustling metropolitan city, housing thousands of people as they take to the streets on their way to work. Once the sun sets, however, I begin to understand why this is the City of Lights. The Eiffel Tower lights up much of the night sky, twinkling at the onset of each new hour. While daytime bakeries close, late-night restaurants and cafes open their doors to the evening-inclined general public. On late night walks back to my apartment, I never fail to notice Parisian couples lounging at an outdoor café, enjoying the nighttime air with a drink and a pastry. Here, it seems to be a widely recognized and embraced concept that Parisians are night-folk.

Long after the sun sets, the lights of Paris are still up and brighter than ever. View from a street corner blocks from the Eiffel Tower.

This is a far cry from the nighttime environment in my hometown, a city on the outskirts of the Metro Atlanta area. I was always used to complete darkness at night, with no late-night city life to brighten the night sky. Even in Atlanta lights don’t shine quite as brightly. While I think the Parisian street scene is charming and I absolutely adore its thriving nightlife, it has left me struggling to get to sleep in the city where the lights never fade.  I’ve only been here a month, but I wonder how all of this consistent light affects the sleeping patterns of the average Parisian relative to the people living in smaller, less heavily lit areas. Does the constant exposure to bright city lights at night-time in cities like Paris result in later sleep cycles that significantly differ from populations living in areas with less nighttime light pollution?

To answer this question, it is important to understand how variation in sleep cycles is defined. People can be sorted into two groups based on their times of wakefulness and alertness – “morning” or “evening” type people. These distinctions refer to a person’s chronotype, which measures individual differences in lifestyle and alertness in the morning versus the evening (Sun 2019). Morning-type people are more likely to get up earlier and exercise more, while evening-types typically go to sleep later, eat later, and wake up later. Based on the social environment alone, Paris seems to encourage more evening-oriented people.

Both chronotypes depends on chemical signaling in the brain to fall asleep at their respective times. Sleep relies on a neurotransmitter known as melatonin, a hormone operating in synchronicity with the onset of nighttime darkness. Melatonin is important for regular and consistent sleep, and delays in its release are expected to play a role in sleep disorders such as insomnia (Shechter 2018). This means that any factor that influences the release of melatonin prolongs wakefulness at night and causes difficulties in getting to sleep. One factor that has continuously shown associations with these delays is presence of light during and leading up to sleep (Shechter 2018). If light is present on a consistent basis, the regular delay of melatonin can cause an adjustment in chronotype towards being more evening inclined. In addition to delaying melatonin production, light alerts parts of the brain that control initiation and maintenance of sleep. (Sun 2019).

As shown above, melatonin is active in the dark. Presence of light inhibits the melatonin pathway and delays sleep.

A study compared circadian patterns between residents of a rural town and members of a small urban area (Carvalho 2013). They had a similar question, and collection of data involved comparison of light exposure and sleep patterns, as well as a structured chronotype questionnaire. The results they obtained show a significant difference between rural and urban populations in spread of chronotypes: the rural subjects showed a predominantly morning chronotype while the urban subjects were predominantly evening-oriented.

As shown above, there is a significantly difference between rural and urban subjects with regards to chronotype.

Their reasoning was that rural workers are exposed to sunlight during the day while they work, which reinforces the need to sleep when the sun goes down. Since urban citizens typically do not work outside, in-the-sun jobs, they are not exposed to as much natural sunlight and do not have their sleep cycles naturally reinforced. Instead, they tend to work technology-based jobs where they are at a computer screen (Carvalho 2014). This results in increased intake of bright and unnatural light, which is independent of the actual daylight (as one can use a computer at night). This would align with the Parisian lifestyle of bright light that is inconsistent with the light of the sun, which tampers with the natural sleep cycle. This reasoning was a strength of the study and proved their conclusion with valid evidence.

A weakness of this study was that it failed to address the possibility of other factors that may have influenced their data. The results they received were very strong, but the influence of light could have been a correlation instead of a causation. They made no effort to test for other variables that may have impacted results, such as timing of social events, parents with young children who require continuous attention, and other non-light related factors.

Based on these results, it looks like the late-night hustle and bustle does have a neurological effect on sleeping patterns. While it doesn’t hurt to be on the computer past sunset, it is clear that continued light during nighttime delays melatonin release on a consistent scale, which can result in the shifting of sleep cycles to an evening chronotype. Turns out there may be some nighttime benefits to living in small towns after all!

References:

Carvalho, F. G., Hidalgo, M. P., & Levandovski, R. (2014). Differences in circadian patterns between rural and urban populations: An epidemiological study in countryside. Chronobiology International, 31(3), 442-449.

Shechter, A., Kim, E. W., St-Onge, M., & Westwood, A. J. (2018). Blocking nocturnal blue light for insomnia: A randomized controlled trial. Journal of Psychiatric Research, 96, 196-202.

Sun, J., Chen, M., Cai, W., Wang, Z., Wu, S., Sun, X., & Liu, H. (2019). Chronotype: Implications for sleep quality in medical students. Chronobiology International, 1-9.

As an avid concert-goer, I am no stranger to long lines and long wait times. Now that I am a tourist, I have become even more familiar with the unavoidable exasperation of hanging out with dozens of other tourists as we wait for the airplane, on the escalators, in the metro, or at the tourist attraction.

Lines at Versailles

Lines at Versailles (If you want to see the full video)

However, even though I am familiar with—and expect—the wait, sometimes I look around and wonder what possesses us humans to be willingly (perhaps begrudgingly) shepherded like cattle to arbitrary waiting spaces for what are often ridiculously long periods of time. There have been times that I have waited in line longer than the actual event I went to go experience: for one of the concerts I went to I waited in line from 4PM when the actual event was more around 8-11PM. For me, it was absolutely worth the wait (and the blisters); however, I admit I can see how to an outsider my behavior must seem incredibly irrational. In Europe, the lines have continued to remain an expected aspect in my life; at Versailles, we waited almost two hours to enter the Palace, and according to some people that wait time was not too bad. No one likes waiting—it is a universally hated experience—so what is the social role of waiting? What compels the people who, like me, are willing to wait these absurdly long times?

Wiesel and Freestone (2019) discuss the practicalities of queues and their implications on wider social systems. In their research, they focus specifically on queuing in urban areas, where material resources may be scarce and allocative measures are necessary. Especially in a city like Paris, I have found that I have had to wait in line for the elevator in our building, the cashier at the boulangerie, the turnstiles at the metro—the list goes on and on. Wiesel and Freestone suggest that queues can help build trust in the surrounding strangers and the structural norms of the city; following the “rules” can be seen as an “indicator of integrity” (Giddens 1991), while breaking the rules and “cutting” others can erode social trust and solidarity and increase anxieties about social disorder due to the diversification particularly present in cities like Paris.

Meanwhile, on a neurobiological level, recent research from Miyazaki et al. give evidence for a “model of waiting” that relies on the neurotransmitter serotonin to mediate whether we continue to wait or not based on probability of getting reward and timing of receiving reward. Previously, other researchers have shown that activating more serotonin release in the dorsal raphe nucleus in mice brains will enhance their waiting times for rewards (Fonseca 2015), while lesioning or destroying those neurons will make the mice more impatient (Miyazaki 2012).

Dorsal raphe nucleus

This article builds upon that idea and considers specific parameters when that serotonergic effect is optimized. Using optogenetic stimulation—or using light to activated increased serotonin release in the brain—they found that in order for increased serotonin to increase wait times, the subject must be fairly confident that the reward will happen in the future. In addition, if the reward was very certain to occur, then the effect is more enhanced when the subjects could not predict when the reward would occur.

Their reasoning is that when the timing is more uncertain, it becomes harder to “reject the possibility that the reward may still come” (Miyazaki et al 2018). Though it used to be believed that serotonin works to alter the perception of time, the researchers in this study did not find a consistent pattern of evidence that shows that. Instead, they propose that serotonin may work emotionally to bias us to more positive outcomes and keep us hopeful that the reward will come soon. Specifically, serotonin may help to mediate between the negative experience we have while waiting in the queue and the positive expect beliefs we have about what we are waiting for. While some of their evidence to support their claim could be strengthened—for example, more data to determine how exactly they are determining whether the mice have a “high confidence” in future rewards—their research provides useful insight into the potential role of serotonin in our emotional decision-making.

What does this mean for me while I’m waiting in line? I probably won’t be able to stop being bored, and it’s not like I can stimulate my own neurons to release more serotonin. But between the idea of “building trust” between me and the other Parisians and knowing that there is a neurobiological basis for our willingness to be patient, I know that my wait will be worth it.

References:

Fonseca MS, Murakami M, Mainen ZF (2015) Activation of dorsal raphe serotonergic neurons promotes waiting but is not reinforcing. Curr. Biol. 25:306–315.

Giddens A (1991) Modernity and Self-identity. Cambridge. 88.

Miyazaki K, Miyazaki KW, Yamanaka A, Tokuda T, Tanaka KF, Doya K (2018). Reward probability and timing uncertainty alter the effect of dorsal raphe serotonin neurons on patience. Nature Communications.

Miyazaki KW, Miyazaki K, Doya K (2012) Activation of dorsal raphe serotonin neurons is necessary for waiting for delayed rewards. J. Neurosci. 32:10451–10457.

Miyazaki K, Miyazaki KW, Doya K (2011) Activation of dorsal raphe serotonin neurons underlies waiting for delayed rewards. J. Neurosci. 31:469-479.

Ryan G, Hernandez-Maskivker G, Valverde M, Pamies-Pallise M (2018) Challenging conventional wisdom: Positive waiting. Tour. Manag. 64:64–72.

Wiesel I, Freestone R (2019) Queue City: Authority and trust in the waiting line. Geoforum. 100:229-235.

Images 1 taken by me, 2 and video by Alyssa Kim.

Image 3: Valdemiro Carlos Sgarbieri

Image 4: Courtesy of OIST

Everybody knows that one wine enthusiast that insists you must let the wine ‘breathe’ and exclaims “Ah, we have some truly wide legs on show here! What a treat!”, in response to the swirl of their glass.

Famous for being the city to where Popes fled following the corruption of Rome in the 14th century, Avignon should also be celebrated for its location in the South of France, a region famous for its wine. Though its sanctity should not be understated, its wine must not be either.

Figure 1. Me and two friends at the Carré du Palais wine tasting.

After walking into the refurbished bank vault at the Carré du Palais, the crisp, cool air hit my skin like the droplets of a bright Sauvignon Blanc with notes of Asian pear and celery. As we all took our places, there were 2 clear wine glasses and 1 small black wine glass that, in my blatant naïvety, I thought was for water. After integrating the sommelier for most of the wine tasting’s duration, he informed me that, in fact, the 1 small black wine glass was for white wine. He stated that our perceived taste of the wine can be influenced by the color because, as everyone knows, a deep yellow is probably an aged Riesling and a deep gold is probably a Chardonnay. This is referred to as ‘crossmodal bias’ (Verhagen and Engelen, 2006), a phenomenon in which one sensory modality (vision) can influence another (taste).

Figure 2. The two clear wine glasses and smaller black wine glass that caused confusion.

I thought this was a very fascinating precaution to take. To investigate the relationship between taste and vision, Rolls and Baylis (1994) recorded singular neurons from five macaques. Food related visual stimuli was presented to macaques and directly after, five different taste stimuli were delivered intraorally. It was found that 29.7% of neurons in the primary taste cortex were bimodal; they were found to have visual responses as well as olfactory responses (Rolls and Baylis, 1994). This discovery exhibits the ability of these sensory modalities to ‘communicate’ early on and can help us understand the phenomenon of crossmodal bias.

The sommelier also made a point to smell the wine deeply before taking his first sip. Following in his footsteps, I tried it. Though I didn’t pick up the hints of black current that he was noting, I did get a sense for the taste that was to come. In 1963, Thompson et al. suggested that sensory information entered its appropriate primary cortex brain region and then, through higher order processing, converged with other sensory modalities to create a more cohesive cognitive stimulus (Thompson et al., 1963). More recent discoveries suggest that the sensory modalities converge much sooner than this (Small et al., 2013). The piriform cortex, a structure within the primary olfactory cortex known to encode for odor memories (Meissner-Bernard et al., 2019), was found to contain neurons that selectively respond to taste (Small et al., 2013). Single neurons in the primary olfactory cortex of 19 rats were found to respond to taste solutions to the tongue (Small et al., 2013). This suggests that there is direct communication between sensory systems. That is, crossmodal bias occurs through exchanges of information between primary sensory systems.

Figure 3. Earlier models suggested a convergence pathway similar to (A) but findings from Small et al. (2013) suggest a schematic more like (B).

Immediately after telling my boyfriend about my cathartic wine tasting, he pronounced that sommeliers are simply full of it. In fact, in a study done by Castriota-Scanderbeg et al. (2005) investigating the differences between sommeliers and naïve research subjects, it was found that sommeliers actually have more refined olfactory and taste perception sensitivity (Castriota-Scanderbeg et al., 2005). 7 male sommeliers and 7 males with no wine tasting training were given either wine or glucose and a subsequent functional magnetic resonance imaging (fMRI) was performed. The left insula, orbit-frontal cortex, and bilateral dorsolateral prefrontal cortex were significantly more involved in wine tasting of sommeliers in comparison to naïve subjects (Castriota-Scanderbeg et al., 2005). Modulated by expertise, these regions represent areas where taste and olfactory stimuli converge and therefore give rise to the representation of flavor (Castriota-Scanderbeg et al., 2005). Moreover, in comparison to glucose, the wine elicited a neural response after the initial taste period which the researchers attribute to the presence of olfactory stimulus (Castriota-Scanderbeg et al., 2005) giving more evidence to the influence of smell on taste.

Over the past 50 years, the well-established organization of sensory systems has been dissolved through discoveries of sensory-sensory connectivity and the influences of one sensory modality on another. So, next time you uncork a nice bottle of wine, or dare I say, screw the top of your $3 bottle, recognize the convergence of your senses.

References

Baylis LL, Rolls ET (1994) Gustatory, olfactory, and visual convergence within the primate orbitofrontal cortex. Journal of Neuroscience 14(9):5437-5452. doi: 10.1523/JNEUROSCI.14-09-05437.1994

Castriota-Scanderbeg A, Hagberg GE, Cerasa A, Committeri G, Galati G, Patria F, Pitzalis S, Caltagirone C, Frackowiak R (2005) The appreciation of wine by sommeliers: a functional magnetic resonance study of sensory integration. NeuroImage 25(2):570-578. doi: 10.1016/j.neuroimage.2004.11.045

Rolls ET, Deco G (2002) Computational neuroscience of vision. Oxford University Press, Oxford (2002)

Small DM, Veldhuizen MG, Green B (2013) Sensory neuroscience: taste responses in primary olfactory cortex. Current Biology 23(4): R157-R159. doi: 10.1016/j.cub.2012.12.036

Thompson RF, Johnson RH, Hoopes JJ (1963) Organization of auditory, somatic sensory, and visual projection to association fields of cerebral cortex in the cat. Journal of Neurophysiology 26(3): 43-364. doi: 10.1152/jn.1963.26.3.343

Verhagen JV, Engelen L (2006) The neurocognitive bases of human multimodal food perception: sensory integration. Neuroscience and Biobehavioral Reviews 30(5):613-650. doi: 10.1016/j.neubiorev.2005.11.003

Photos

Figure 1 and 2 were taken by me

Figure 3: Small DM, Veldhuizen MG, Green B (2013) Sensory neuroscience: taste responses in primary olfactory cortex. Current Biology 23(4): R157-R159. doi: 10.1016/j.cub.2012.12.036