Evolution News: The Hippocampus, Memory and Sex

Elaine Meinel Supkis

Understanding the role of hippocampus in our brains leads to interesting insights into how evolution and sex works. Also, lots of exercise affects the hypothalmus. It is also the home base of the ability to remember the past and navigate in the present.

I remember my emotional flip flops from back then, this is why I became a hippie chick, I suppose.

A new US study has revealed that teenage mood swings may be explained by biological changes in the adolescent brain.

Mood swings and anxiety, often caused by stress, are well known characteristics of puberty.

A physiologist at the State University of New York, Sheryl Smith, and her research colleagues experimented on female adolescent mice and showed that their brains respond to stress in a different way to adults and pre-pubescent individuals.

Anxiety is regulated by the brains's principal inhibitory neurotransmitter, GABA (gamma-amino-butyric-acid) which counteracts the effect of glutamate, an excitatory neurotransmitter in the brain's limbic system.

Stress causes the release of a steroid known as THP (allopregnanolone) which in adult and pre-pubescent individuals increases the "calming" effect of GABA in the limbic system. However, Smith and her team found that THP had the opposite effect in adolescent mice.

One might say, youth is drunk on the pressed wines of evolution. Namely, the need, the urge to emotionally interact with others is at its height when the sexual urges begin to hammer their way into an organism's life. Namely, when very young, the little ones whether they be lambs or fawns or cubs, they focus on relationships with the immediate family. This means sticking to home, listening to mother and avoiding strangers.

Then the harmones for sex enter the bloodstream. Suddenly, the deep urge to be careful, avoid strangers, stay at home, obey mom, vanishes in a tsunami of harmones screaming, 'Go outside, ignore your stupid mother and find as many strangers as possible and have sex with them!' In other words, the fledgling birds fly from the nests, the young rams sniff the fall air and go looking for strange ewes, the young humans slip out of the house and go to war or the local pub and look for loose females.

Of course, humans try to control this dangerous urge via marriage and passing lots of rules and laws about rape, how women dress and other details designed to curb the urge to go out and have sex no matter what. Keeping teenagers out of trouble is very difficult because of these organic urges that are shared by nearly all living creatures that have sex. As brains evolved, deep inside, the home of sexual urges was carefully embedded and the ancient urges are not to be denied.

Here is the actual study in question.

Hui Shen1, Qi Hua Gong1, Chiye Aoki2, Maoli Yuan1, Yevgeniy Ruderman1, Michael Dattilo1, Keith Williams1 & Sheryl S Smith1

Puberty is characterized by mood swings and anxiety, which are often produced by stress. Here we show that THP (allopregnanolone), a steroid that is released as a result of stress, increases anxiety in pubertal female mice, in contrast to its anxiety-reducing effect in adults. Anxiety is regulated by GABAergic inhibition in limbic circuits. Although this inhibition is increased by THP administration before puberty and in adults, during puberty THP reduces the tonic inhibition of pyramidal cells in hippocampal region CA1, leading to increased excitability. This paradoxical effect of THP results from inhibition of 4 GABAA receptors. These receptors are normally expressed at very low levels, but at puberty, their expression is increased in hippocampal area CA1, where they generate outward currents. THP also decreases the outward current at recombinant 42 receptors, and this effect depends on arginine 353 in the 4 subunit, a putative site for modulation by Cl-. Therefore, inhibition of 42 GABAA receptors by THP provides a mechanism for the generation of anxiety at puberty.

We know that sex doesn't happen without some excitement and Mother Nature devised a devious system for the mobile organisms: battles for sex. On top of that, females formulated a second front in this fight for sex: picking pretty males (the 'Favio' factor) and selecting only those males who build them a nice house and demonstrate baby-feeding skills.

The red in tooth and claw mating that evolved with many mammalian predators stands in contrast with a number of bird's strategies which focus on domestic abilities or vanity. It is interesting that birds are the main descendants of dinosaurs and we nearly universally view dinosaurs as bloody, vicious sex-fiends. I would not be the least bit surprised, if I were a time traveler, to find dinosaurs to be very colorful and beautiful to behold with the males strutting about, chests out like giant turkeys, booming their armorous songs while the females eyeball them.

For example, snakes don't fight when they mate, they simply mob the female snakes. Ditto amphibians. Their hippocampi tells them to wander as far as possible, seeking these lovely, shiny, slippery delightful girl snakes and they follow their noses. The interaction of the nose, memory and sex is extremely strong in all living organisms that have sex which requires hunting down a female and getting her to open up.

A complex bouquet of harmones and phermones interact with more than one part of the brain and these are all tangled up with the ability to find one's way about the place and remembering stuff that is important and all those other survival/sex skills.

These forces can, when unbalanced or the environment is bad, cause death and destruction. The human impulse to kill and rape is very highly developed and is easily triggered by these organic processes because we evolved as a very nasty, violent branch of the monkey family. We also have the biggest brains which can easily go haywire if the harmones and such are even slightly out of whack.

Our evolution as stone-throwing, wandering primates is deeply intertwined with our hippocampus.

The hippocampus is a part of the brain located under the temporal lobe (humans and other mammals have two hippocampi, one in each side of the brain). It forms a part of the limbic system and plays a part in memory and spatial navigation. The name derives from its curved shape in coronal sections of the brain, which resembles a seahorse (Greek: hippos = horse, kampi = curve).

In Alzheimer's disease, the hippocampus becomes one of the first regions of the brain to suffer damage; memory problems and disorientation appear among the first symptoms. Damage to the hippocampus can also result from oxygen starvation (anoxia) and encephalitis.

In the anatomy of animals, the hippocampus is phylogenetically among the oldest parts of the brain. The hippocampal emergence from the archipallium is most pronounced in primates and cetacean sea mammals. Nonetheless, in primates the hippocampus occupies less of the cerebrum in proportion to cerebral cortex among the youngest species, especially humans. The significant development of hippocampal volume in primates correlates more with overall increase of brain mass than with neocortical development.

It is interesting that the main mental diseases that are age-related hit the sex/memory headquarters first. This is because most species die long before they become senile. Namely, they have as many babies as possible and this kills them eventually. They don't have menopause, for example. Humans, being very social animals, have evolved things called 'cultures and societies' which vary greatly in quality and style but all have one effect (unless suicidal): they protect the breeders sufficiently that they can become old.

Even when going senile, the elderly had several major functions: to inhibit wild changes and behaviors in the young due to a natural desire for continuity and of course, they baby sat the very young and fed the all-important Goddess of the Hearth: the fires. Since the elderly get more easily chilled, they happily undertook this tedious chore which was, for them, not tedious at all but a welcome rest. And in the Ice Ages, the infants could cuddle in grandpa's or grandma's lap while he or she fed the holy fire and since little children insist on hearing the same story 1,000 times over and gramps and granny couldn't remember too many stories anyway, both were happy as can be, repeating the same stories over and over again, patiently and even with intense happiness.

So humans extended their life spans even while losing the hippocampus responses. Indeed, those that lost it were the most useful to the Ice Age people. When the Ices melted, the newly opened lands led to a tremendous amount of nomadism and nomads leave the very elderly behind to die. But at this same time, cities were invented and in these new social set-ups, humans could happily age in peace and the all-important fire was of course, even of higher importance.

Here is also an interesting tidbit: the hippocampus also changes how it stores memory depending on the age of the human.

Autobiographical memories can differ for special periods of life. People recall few personal events from the first years of their lives. The lost of these first events is called childhood or infantile amnesia. People tend to recall many personal events from adolescence and early adulthood. This effect is called the reminiscence bump. Finally, people recall many personal events from the last few years. This is called the recency effect. For adolescents and young adults the reminiscence bump and the recency effect coincide.

It is again, interesting how we evolved: the baby's brain works nearly nonstop, learning basic skills like moving about, picking up things, putting things together, talking, social interactions. Things happen to a young child but they are immaterial unless they are huge events. Even then, the brain strives to conceal or hide the actual memory to protect the young human's brain. I was hit by lightning when only five and had zero recall for it until I dug up the memory through detective work and self-analysis.

The need to remember 'stories' and 'events' rises rapidly when sex kicks in. The youth have to rapidly figure out this new social realm and there are many, many dangers there. Cannibalism, homicide, betrayal of trust, damaging the female so she can't successfully raise the babies, etc. This requires amassing lots of data rapidly and being able to compare events. Since plotting to hunt down females from other tribes is deeply embedded in this part of the mind, it is no surprise to see this in action within the brain as an ability to think like a diplomat. Namely, the best and safest way to get females and to gain their trust and cooperation is to negotiate with their elders including the more senile members.

If they are safely drawn into one's enterprise, the prize which is a female willing and able to have and raise young new humans, is easily gotten. So brute force didn't dominate at all, the most successful humans were the ones with bigger and bigger brains who could remember more and more subtle details and story-like information which is good for negotiating tribal relations when seeking mates.

The discovery of place cells led to the idea that the hippocampus might act as a cognitive map — a neural representation of the layout of the environment. Recent evidence has cast doubt on this perspective, indicating that the hippocampus might be crucial for more fundamental processes within navigation. Regardless, studies with animals have shown that an intact hippocampus is required for simple spatial memory tasks (for instance, finding the way back to a hidden goal).

Without a fully-functional hippocampus, humans may not successfully remember where they have been and how to get where they are going.

It is rather simple. The organisms setting out to hunt for sex partners go far afield. And since they are following their noses and looking for colorful signs of possible mates, they can get lost very quickly and the need to find one's way home after wild sex is of great importance because an unknown location equals danger. Note how a cat reacts when moved to a new home: it hides immediately and only very gingerly, explores the new place, a little at a time and with all whiskers a-tremble.

And a deteriorating mind often resorts to mindless activity to stimulate the hippocampus.

A. M. Huang1, C. J. Jen1, H. F. Chen1, L. Yu2, Y. M. Kuo3 and H. I. Chen1

Summary. This study was to examine the effects of treadmill exercise on the expression of brain-derived neurotrophic factor (BDNF) in rat hippocampus. After 1-wk treadmill familiarization, animals in exercise groups received a 4-wk exercise training or an acute exercise. They were sacrificed 2 h or 2 d after exercise and their hippocampal BDNF mRNA and protein levels were determined. We demonstrated that 1) hippocampal BDNF mRNA and protein levels were both elevated in response to exercise training at 2 h after the last run but not after 2 d; 2) an acute moderate exercise (1 or 3 d) increased BDNF protein levels; 3) acute severe exercise increased BDNF protein and mRNA levels in animals under a familiarization regimen, while suppressed the BDNF mRNA level in rats without treadmill familiarization, paralleling the stress effect of immobilization/water exposure. We conclude that compulsive treadmill exercise with pre-familiarization acutely upregulates rat hippocampal BDNF gene expression.

For a long time I have asserted Bush is suffering from Alzheimers. His restlessness and need to exercise no matter what while running over people or falling down are classic signs. Many Alzheimer patients wander off and get hopelessly lost. Some die. They don't understand why they do this, they just start walking and can't stop. I remember my grandfather doing this at night. I would have to catch him and lead him back to his bedroom or back to the house.

Ronald Reagan had severe Alzheimers while in office. Wilson had a stroke and still ruled America disastrously. Today we have the ability to see if someone is suffering from these disorders. It should be a requirement for staying in office that the brain be functional. More than one Senator voted in his office while nearly brain dead (um, sometimes all of them, heh).

Bush should be removed for medical reasons. And he is a criminal. Heck, just arrest him.

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