The Evolution of Love

Let me tell you about the birds and the bees. And the flowers and the trees. And a thing called love…
But hey … what is LOVE, except for the most popular topic of song lyrics?

What is Love?
The urban dictionary gives the following definition: “Love is nature’s way of tricking people into reproducing” [1]. Hm… why didn’t we just continue to be self-copying RNA as described in “The Selfish Gene” by Richard Dawkins, or simply procreate by cell division [2]? The clue is that sexual reproduction brings enormous advantages in terms of fitness: Mutations occur naturally in every organism all the time. Some may be harmful, some without impact and others may be highly beneficial. Maybe a mutation in a structural protein could give a protist sturdier ciliaries, allowing it faster movements and a great advantage in escaping predators. However, only the individual carrying the mutation will benefit from it unless it is shared. And basically, sexual reproduction is nothing else but sharing your genome with someone else. This someone will not benefit in person, but his and your offspring will. Thus sharing is caring. But does caring equal love?

Source

I'm Too Sexy...
In general, mating means higher cost for an individual at first, but pays off with increased fitness of its progeny and gene propagation. But of course, not every individual wants to mate with any other. Hence, mating strategies developed to maximize benefit. Mating strategies vary in complexity: a pretty straightforward strategy is to release attractive molecules to acquire a random partner. However, the more costly the reproduction itself, the more prudence in partner choice is advised. The decision about a partner is usually made by the female, thus males of many animal species have developed specific attributes and/or courtship behaviors that may not serve any practical purpose other than attracting a female’s attention and influencing her choice.
Birds give great examples of this: peacocks grow their beautiful and immense tails to impress females. These have no use other than to signal “I am so fit and healthy, I can afford an entirely useless, giant plumage!” (see also 'You Have Beautiful Eyes, Hundreds of Them'). Similarly, bowerbird males construct little lodges from sticks, grass, and leaves, which they even decorate with flowers, shells, and other colorful and shiny things they collect. If the lodge is impressive enough and the female decides to mate, they entirely abandon the lodge to build a nest suitable for breeding elsewhere.
Humans, too, possess attributes that serve reproductive rather than survival purposes. Compared to other primates, humans have features such as “concealed ovulation, extended female sexuality when not fertile, large visible breasts even when not lactating, large spongy boneless visible pensises relative to body size even when not sexually aroused, relative hairlessness that reveals skin quality, full lips that may mimic female genitalia by exposing skin that simulates mucosal membranes”, as discussed in detail by psychologist Lawrence Josephs [3].

You and Me, Forever
But mating alone does not yet guarantee successful procreation. A lot of further effort needs to be invested by parents to actually ensure the survival of offspring, especially in higher mammals. For humans, this can be up to twenty years! For this purpose, nature developed strategies beyond the "hit and run" approach to make mating partners cooperate until their progeny can survive on its own. Bonding mechanisms cause partners to team up and cooperate until descendants can survive independently [3,4]. This may lead to monogamy (or serial monogamy) as a favored type of relationship.
Nowadays, psychologists discuss compassion, a feeling most of us would also associate with love. Compassion also developed to ensure survival chances for vulnerable offspring because it motivates individuals to join forces and cooperate for the sake of their progeny [5]. Even early evolutionists such as Darwin considered what he called “sympathy” to be one of the strongest human instincts. While all of this totally makes sense, it does not really fit our modern-day definition of “love”.

LOVE IS THE ONLY SOCIALLY ACCEPTED FORM OF MADNESS

Maybe, it is more appropriate to talk about the psychological term “romantic love”. Psychologist James Leonard Park provides a sarcastic explanation of romantic love as a hoax or urban legend [6]. Indeed, considering archeological finds from the beginning of mankind, there is evidence for different forms of courtship behavior and for the concept of marriage, i.e. partnership between man and woman in order to maintain monogamy and raise children. Still today across the globe, people get married for practical reasons only, without any romantic consideration. Where does romance come into play then? Apparently, it is the relatively modern invention of medieval troubadours and minstrels in France [7]. Since then, European culture has spread all over the world, the newly invented concept of romantic love has entered folk psychology and is ubiquitous in songs, novels, television, and movies. Cultural imprinting, one could say.


You Drive Me Crazy
Nonetheless, most of us have experienced romantic love, and it is commonly perceived as an altered state of consciousness or “the only socially accepted form of madness” [8]. Not only because of these definitions, involving consciousness and insanity, psychologists and neurobiologists began to explore what underlies romantic feelings in the brain. Even though research has so far correlated brain regions and autonomous nervous system activity with feelings of love and identified some brain chemistry that elicits affection, science is far from answering the question: What is love?
It's good to know that instead, there are plenty of songs still to come that can tell us the answer.

[1] http://bit.ly/1fTAtUl
[2] Dawkins, "The Selfish Gene", Oxford University Press, New York, 1976
[3] Josephs, Am Acad Psychoanal Dyn Psychiatry, 2010
[4] De Boer, Neuroscience, 2012
[5] Goetz, Keltner and Simon-Thomas, Psychol Bull, 2010
[6] http://bit.ly/1mHJD9x
[7] http://bit.ly/1g2veC6
[8]http://bit.ly/1nnGFXd

by Bettina Schmerl, PhD Student AG Shoichet
This article originally appeared 2014 in CNS Volume 7, Issue 2, Neuroscience of Love

You have Beautiful Eyes, Hundreds of Them!

What do people look for in a partner? Many of us would love to know what aspects of our appearance are of most interest to potential mates. Well, we could start by posing the question 'What do people look at in a partner?' After all, what the eye does not see, the heart does not grieve over or in this case throb for.

Avian Eyetracking Shows Peahens Checking Out Males' Train Feathers
This is one of those research questions, however, where straightforward questionnaire data are likely to raise suspicions. How many people are going to admit that they look straight at someone's buttocks or cleavage? Eyetracking, on the other hand, can reveal a great deal about what people attend to, and has delivered such edifying conclusions as: Men seem to like to assess each other's crotches [1]; women check each other out as much as they do men [2]; and men look longer at larger breasts (even when controlling for the larger area of the visual field they occupy) [3].

Picture reproduced with permission from Yorzinski et al, J Exp Biol, 2013

A recent novelty, however, is the application of eyetracking to the romantic interests of birds. And no better bird to begin with than the peacock, famous for its eye-catching train of iridescent feathers, rattled in mating displays. Of course, in the animal kingdom it tends to be the women who do the ogling, so a recent study tracked peahens' eye movements while the males strutted their stuff [4].
The peahens were not especially impressed, spending less than a third of their time even looking at the male at all. Nor were they interested in everything he had to offer. The upper train, where most of the eyes are located, was of relatively little interest. Instead, the females' gaze lingered on the lower train, which they scanned from side to side in a way that suggests they were assessing its symmetry, an important feature in sexual selection [5].
So how can we make sure our next date results in love at first saccade? The authors offer a somewhat disheartening speculation. Briefer viewing times may indicate simply that a trait is much easier to assess. Peahens may look less at train eyes simply because it is very easy to see whether a male has fewer than required, and he may then be rejected without further ado [6]

[1] http://bit.ly/NCem7I
[2] Rupp and Wallen, Horm Behav, 2007
[3] Gervais et al, Sex Roles, 2013
[4] Yorzinski et al, J Exp Biol, 2013
[5] Moller and Thornhill, Amer Nat, 1998
[6] Dakin and Montgomerie, Anim Behav, 2011

by Luke Tudge,
This article originally appeared 2014 in CNS Volume 7, Issue 2, Neuroscience of Love 

Case Study: A new study from Caltech suggests jellyfish may need sleep too.

Researchers at the California Institute of Technology have found evidence that at least one type of jellyfish engages in a very unexpected behavior: sleep. The study, published by Ph.D. candidate Ravi Nath and his fellow researchers in Current Biology [1] in September, showed that Cassiopea jellyfish passed several criteria established in their lab to demonstrate they were engaging in a behavior that could be considered sleep.

The finding comes as a surprise to the scientific community, as previously sleep was thought to be an activity performed only by more complex organisms with central nervous systems: humans, dogs, fish, even worms. Now, adding to the mystery of why organisms sleep, there is one without a brain that does it too.

SLEEP: A BASIC REQUIREMENT IN THE ANIMAL KINGDOM

To establish that the jellyfish were sleeping rather than engaging in other behavior, the researchers set up three criteria: a regular period of diminished activity, decreased responsiveness to stimuli during this period and an increased need for the hypothesized sleep behavior when it was not getting enough. The jellyfish passed all three.

Sleep - it's a NO-brainer!
Formal testing revealed that the jellyfish pulsed 30% less during this period of diminished activity and could be “awoken” with food or prodding, ruling out other possible states such as coma. The researchers tested responsiveness by removing the floors from under the jellyfish at random times; in the hypothesized sleeping phase, they would float around before swimming to their preferred place on the floor of the tank. A need for sleep was operationalized by shooting water through the tank every 20 minutes, keeping the jellyfish from attaining this restful state; during the wakeful period the following day, the jellyfish engaged in lower levels of activity than usual.

Image source: prilfish via Flickr

Cassiopea, the “upside-down jellyfish” have a non-centralized radially symmetric nerve net, a diffused organization of nerve cells throughout the body with no large centralized concentration (a brain) [1]. However, like organisms with central nervous systems, theirs functions using action potentials, synaptic transmission, neuropeptides and neurotransmitters. This commonality suggests maintenance of the nervous system at a very basic level may be a reason organisms need to sleep.
Cnidaria, the phylum of Cassiopea, branched early on from the evolutionary line of human beings. The researchers suggest that this signifies “sleep is rooted in basic requirements that are conserved across the animal kingdom.” [1] More research however, will need to be done to determine whether this behavior evolved in Cnidaria separately, or whether it is truly an early behavior in our evolutionary history.

By Alex Masurovsky, MSc Student Berlin School of Mind and Brain
This article originally appeared December 2017 in CNS Volume 10, Issue 04, Sleep 



[1] Nath et al., Curr Biol, 2017; 
[2] http://nyti.ms/2fE9JuC
[3] http://bit.ly/2hF7bgC

Don’t Give Up On Your Dreams. Sleep On!

Sleep is an almost universal behavior throughout the animal kingdom. Humans spend roughly a third of their life sleeping, therefore we can call it a truly integral part of life. However, is sleep just a uniform state of unconsciousness opposite to being awake? 

Like most animals, humans' sleep and wakefulness are modeled by inner circadian rhythms and external cues, so-called zeitgebers (see also the article on chronotherapeutics on page 10), to a period of roughly 24 hours. In particular, sunlight is able to reset our inner clocks, thereby enabling us to adjust our daily rhythm, e.g. after intercontinental flights. Not sleep itself, but rather when we sleep is regulated by the suprachiasmic nucleus in the anterior hypothalamus, which functions like an internal clock and is affected by environmental inputs (again, especially sunlight, which reaches the hypothalamus via the retinohypothalamic tract) [1].

sleep well; source:  http://bit.ly/2yFBDBZ

Is sleep just a consequence of the brain being less active because it's tired? Although this explanation might appeal to many fellow PhD students, sleep is characterised by a complex pattern of brain activity! Key aspects of sleep are: little motor activity, little response to stimulation, typical postures (like lying down curled up) and the state being quite easily reversible (distinguishing sleep from coma, for example) [1]. These features can be monitored by conventional electrical recordings, including electromyography and electroencephalography (EEG). When people (and animals) fall asleep, EEG recordings show a drastic change in neuronal activity.

Sleep = Brain Activity?!
Broadly speaking, sleep comes in two flavors: REM (rapid eye movement) sleep and non-REM sleep, which consists of four stages of characteristic brain activity patterns. Wakefulness typically comprises approximately 20 Hz waves. When people fall asleep, this frequency falls to 10 Hz and entering sleep stage 1 is characterized by mixed frequency patterns, light muscle activity and slow rolling eye movements. Likewise, body temperature and metabolism slow down. The next stage (stage 2) is characterized by 12-14Hz activity sleep spindles and K complexes, biphasic high-voltage waves. The sleep stages 3 and 4 are also referred to as slow-wave sleep, as EEG recordings of these phases are dominated by delta waves of only 0.5-2Hz frequencies. In contrast to the characteristics of the four stages of non-REM sleep, brain activity in REM sleep resembles wakefulness, with some populations of neurons being even more active when you are in REM sleep than when you are awake. REM sleep is accompanied by an increase of body temperature and metabolic rate but an almost complete loss of muscle tone, except for the eyes which characteristically move rapidly [1].

Sleep phases; source: http://bit.ly/2zp9M61

Interestingly, it is easier to wake a person up during REM sleep than stage 3-4 of non-REM [2]. As brain activity during REM sleep pretty much resembles EEG patterns during wakefulness, it may not seem surprising that most dreaming occurs during these phases of a night’s sleep. Dreaming can also occur during non-REM sleep, although with a much lower incidence and slightly different characteristics [2].

Sleep is not a uniform State!
Each sleeper moves through REM and the 4 stages of non-REM sleep several times a night in cycles of 90-110 minutes. During a night’s sleep, the stages do not succeed eachother in a particular order and also change in length. For example, phases of REM sleep can take 1-60 minutes and may be accompanied by brief periods of waking [3]. The cycles through the different phases of sleep, the sleep “architecture”, differ between subjects, single nights, and also change with age. In early childhood, much more time sleeping is speny in deeper sleep stages 3 and 4 whereas in older age stage 2 sleep dominates [4]. (See also our article in "The Aging Brain")

How you sleep changes with age

But what's the point of such a complicated sleep architecture? As also discussed in the articles “Evolutionary basis of sleep” on page 5 and “Sleep and learning ” on page 6 of this issue, sleep serves important functions for the body and thus is necessary. However, being unresponsive to potential threats is a significant problem, which is in part circumvented by the fact that we alternate between periods of deeper and lighter sleep [3].
As you can see sleep is much more than just the most unproductive period between two days. It is quite complex and interesting and science still needs a lot of effort to unravel all its mysteries. Therefore, everyone should spend more time in personal field studies. For example, at home - sleeping.

Good Night!

[1] Kandel, Schwarz, Jessel. Principles of Neural Science, 2003
[2] Staunton, Naturwissenschaften, 2005
[3] Voss, Rev Neurosci. 2004
[4] Zepelin et al., J Gerontol, 1983


by Bettina Schmerl, PhD Student AG Shoichet
This article originally appeared Dedcember 2017 in CNS Volume 10, Issue 04, Sleep 

„Mum, how do dolphins sleep?“: Sleep throughout the animal kingdom

Have you ever wondered whether your dog sleeps like you – and yaps because he is probably dreaming about the mailman? Do all animals need sleep as much as we do? And how on Earth do they continue swimming or even flying during sleep?

Smart because of Mattresses?

First of all, we should define what we are talking about: Sleep can be characterized in many ways, but without electroencephalography with wild animals, we should focus on the behavioral definition: Sleep is when the animal exhibits a rapidly reversible state of immobility and reduced responsiveness to external stimuli. Furthermore, an increased drive for sleep (rebound effect) is expected after sleep deprivation [1].

Lets start with our closest relatives: Great apes exhibit monophasic sleep (like humans and unlike the majority of other mammals), meaning that they concentrate their sleep in one period per day. Theories claim the reason for this is that they are (like us) capable of building a comfortable and safe sleeping platform - allowing them to sleep more safely and therefore more deeply. Maybe our cognitive abilities just came from very comfy beds [2]?

Apes build comfy beds

 

But there are other intelligent animals that definitely have no mattress to sleep on. Many dolphins are able to rest one half of their brain while the other one controls breathing, for which marine mammals have to come to the surface. This phenomenon, which some of us would love to do during boring seminars, is called uni-hemispheric slow-waves (USW). It enables dolphins, whales and also many birds to rest one hemisphere at a time with the contralateral eye closed, changing to the other one after about two hours [1]. Brain waves similar to slow-wave sleep and REM sleep in humans have been recorded in flying frigate birds which migrate for several months at a time [3]. Remarkably, when in REM sleep, these birds as well as some other mammals like the sperm whale also show bi-hemispheric sleep. However, this behaviour can only be found on the ground – or in the case of sperm whales while floating vertically in the ocean, holding their breath for a long time [4]. A strategy like this would never work in many sharks, since they need constant flow through their gills to be able to breathe. Some seem to solve this problem by doing “yo-yo diving“: First they swim to the surface to then glide downwards, giving themselves a short period of rest [5].

Different Animals sleep differently

The sleeping behaviour of terrestrial animals can also be very different from ours: Does anyone sleep while standing - No?! Horses and other bigger herbivores often do, with help of their stay apparatus, which consists of ligaments and tendons that lock into place. Still, many of them need to lie down for REM sleep as it comes with strong muscle atonia. Due to this, horses, giraffes and also elephants actually end up having much less sleep than we are used to, getting away with just 2-4 hours per day [6]. Many short naps seem to be more beneficial for these animals, since it enables them to spend more time alert when predators are around.

Who wouldn’t like to be capable of skipping 5-6 hours sleep per day in order to prepare the next lab meeting? New-born orcas outperform us a lot when it comes to little sleep: They stay awake for one full month after birth, and only rest while pressing their body against their mother. Compared to this, big brown bats and hairy armadillos lead a pretty relaxed life, sleeping for roughly 20 hours per day [6]. 

Image Source: http://bit.ly/2B1GiM7

So far we were mostly talking about sleep similar to human non-REM. But do animals also dream? Of course, no one can ask a cat whether it was recently dreaming of mice. Anyway, many mammals, birds and even reptiles show physiological patterns with consistent with REM sleep. Dragonflies have 350 REM cycles per day, each of them lasting 80s [7] and the platypus spends approximately 5.8-8 h/day in REM [8]. REM sleep is sometimes seen as a key feature during evolution of the amniote – the common ancestor of mammals, birds and reptiles that lived more than 300 million years ago [7]. However, octopus also seem to have REM like sleep patterns that go along with changing colours and twitching of their arms [9].

Yet, the animal kingdom consists of more than vertebrates. What about insects, nematodes and porifera (sponges)? While for porifera there is no evidence of sleeping behavior, the fruitfly D. melanogaster has not only been shown to have sleep-like resting patterns but also exhibit cognitive impairment upon sleep depriviation [1]. A fatigue period (lethargus) before moulting in C. elegans suggests that sleep is somehow connected to development and related to neuronal changes [10].

What's the Purpose behind Sleep...?

Of course most sleep studies focused on very few animals from each taxa so far. For instance, just 50 out of 60000 vertebrate species have been tested for all sleep criteria so far and not all of them were found to meet all of the criteria. Nevertheless sleep-like behavior seems to be present in various animals. Can we assume that all these animals sleep for the same reason - and if so what is the reason?

Over years, several theories on the function of sleep have been developed. The original idea that sleep is mainly necessary to conserve energy seems quite unlikely nowadays since it decreases metabolism by very little amounts (5-10%), whereas hibernation saves a lot more energy [11]. Another very prominent idea is that sleep is important for learning and memory consolidation (see article of page 6). Even though there is evidence for a role of sleep in memory, it is still disputed what this role exactly is – ranging from memory deletion during REM sleep to maturation of memory circuits [12]. Recently, sleep has been linked with a restorative function in the central nervous system, leading to a clearance of free radicals and other metabolic waste that accumulates during wakefulness [13]. While many of these processes definitely occur during sleep, they don’t explain the great variation in sleep needs and patterns throughout the animal kingdom. 

Do all animals sleep for the same reason?

Trying to address this, some researchers now regard sleep as a state of adaptive inactivity, optimizing the timing of behavior according to prey/food availability and threats in the environment. In this scenario, continuous wakefulness implies the greatest energy demands but maximizes niche exploitation. This can explain why giraffes sleep so little (they have a very low-caloric diet and a high threat of predators). For bats that feed specifically on insects being active between dusk and initial hours of darkness, on the other hand, a longer period of time awake would be highly maladaptive since it increases their risk of becoming prey [14].

... we don't fully know (yet)!

Exploring sleeping behavior of other animals can, therefore, help to clarify its function in humans. While sleep deprivation in humans and rodents so far suggests that sleep influences cognition, emotion, immunity and memory, the function of sleep can still be substantially different when looking at all animals that exhibit sleep-like resting behavior. We should all be aware that, as put by Michel Jouvet, a famous sleep researcher who just passed away, "it’s not enough to use the brain of your experimental animal, it’s also necessary to use your own”. 

Annika Reinhold, MSc Student MedNeuro

References:

[1] Siegel, 2008, Trends in Neurosciences

[2] Shumaker et al., 2014, American Journal of Physical Anthropology

[3] Rattenborg et al., 2016, Nature Communications

[4] Miller et al., 2008, Current Biology

[5] http://bit.ly/2jd1XfV 

[6] http://bit.ly/2zsCd59 

[7] Shein-Idelson et al., 2016, Science

[8] Siegel et al., 1999, Neuroscience

[9] http://bit.ly/2jmPMc6 

[10] Sing et al., 2013, Sleep

[11] Assefa et al., 2015, AIMS Neuroscience

[12] Diekelmann & Born, 2010, Nature Reviews Neuroscience

[13] Xie et al., 2013, Science

[14] Siegel, 2009, Nature Reviews Neuroscience

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