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The Brain Stem

by Andy Habermacher | 2022 Mar 26 | The Human Brain

The base of your brain

The brain stem sits lower in the brain and is often considered the “primitive” part of the brain. This may be an oversimplified way of describing this part of the brain – but it does control many life-sustaining functions so without it we are goners!

The parts of the brain stem

The brain stem is often referred to as the “primitive” part of the brain or famously the “reptilian brain”. This terminology was proposed by neuroscientist MacLean who wrote in his book, on the evolution of the brain, how different parts of the brain could be ascribed an evolutionary function. This “triune model” has become a simplified model of the brain and because of its appealing simplistic nature has been used and abused by many people including Daniel Goleman one of the father’s of emotional intelligence. I have also used it often. Neuroscientists and I know that this is a very simplified model of the brain. But we also know that there is some truth to it and so for the sake of ease of explanation and appeal to lay audiences this is still often used.

The language is also intuitive and easy to grasp. The logic goes that all organisms have a version of the brain stem, and this is what most simple brains are in essence – the equivalent of the brain stem often in miniature form in simple organisms. Also, in the development of the brain the brainstem forms first and then the structures grow out of this, and the cerebrum is formed last. So, the standard logic goes that the brain stem houses our primitive living functions. Let’s review briefly.

The brain stem is categorised into three sections:

Medulla Oblongata
Pons
Midbrain

What is also important is that 10 of the 12 cranial nerves target or sources form the brain stem.

The medulla oblongata (normally just called the medulla) is the transition zone of the brain into the spinal cord. It houses a number of critical functions such as two of the three respiratory groups controlling breathing and monitoring this. Also, cardiac control and regulation, controlling heartbeat and monitoring this and also controlling blood pressure. The vomiting reflex is also controlled in the medulla through a region called the area postrema that monitors chemicals in the blood.

Above the medulla sits the pons which is dense in cranial nerve nuclei and connects the medulla to the thalamus but also coordinates activity in the hemispheres of the cerebellum (I covered the fascinating cerebellum in lbR-2021-01). It also houses the respiratory centre that coordinates with the other two respiratory centres in the medulla. The locus coeruleus is also located here which is a major centre for the synthesis of norepinephrine and a key part of attention and also curiosity circuits.

Above the pons sits the midbrain which has the other five cranial nerve nuclei but also a number of other important regions that crop up again and again in neuroscientific research. The periaqueductal gray is an area of neurons that are involved in multiple processes including pain desensitisation. The substantia nigra and also the ventral tegmental area are also located here and these are two key dopamine synthesising centres. Similarly, the rostro medial tegmental nucleus is a GABAergic centre. But is also houses the reticular formation (with the pons) and this is involved in arousal and consciousness systems. There are also strong connections to the lower motor neurons which is why regions her are also implicate d in Parkinson’s disease.

So, we can see that the brainstem does indeed house a whole host of living critical functions without which we cannot survive. This is why damage to this part of the brain is particularly disruptive and more often than not life threatening e.g. snapping the neck at the top of the spinal cord as we see in many old spy films.

On one hand though we can also see that some things which we consider primitive such as aggression are not actually driven from this region of the brain but more the critical life reflexes are such as heartbeat, breathing, arousal, and attention.

Though you may think that the brain stem is all we need to survive, a condition known as anencephaly shows this is not the case. Anencephaly is a condition in which babies are born without a cerebrum. These babies die shortly after birth which is a stark reminder that the brain does operate as a whole, and functions are spread over the brain.

So that simplified version of what the brain stem is does hold true, but we shouldn’t forget that the brain is incredibly complex and, particularly in human beings, has developed to operate across regions whether “lower” or “higher” – these regions often do not grab the neuroscience and popular science headlines. But without them you would surely not be here●

References

Kolb, B. & Whishaw, I. Q. (2009). Fundamentals of human neuropsychology: Sixth edition. New York, NY: Worth Publishers.

MacLean, P. D. (1990). The triune brain in evolution: Role in paleocerebral functions. New York: Plenum Press.

Singh, Vishram (2014). Textbook of Anatomy Head, Neck, and Brain ; Volume III (2nd ed.). p. 363. ISBN 9788131237274.

Haines, D; Mihailoff, G (2018). Fundamental Neuroscience for Basic and Clinical Applications (5th ed.). ISBN 9780323396325.

“Brainstem | Definition, Structure, & Function”. Encyclopedia Britannica.

“Cranial Nerve Nuclei and Brain Stem Circulation”. Neuroanatomy Online.

Serotonin

by Andy Habermacher | 2022 Mar 25 | The Human Brain

The mood modulator

Selective serotonin reuptake inhibitors (SSRI) may sound like gibberish to many but are in fact one of the most common drugs on the planet. These SRIs are used in mood disorders, particularly depression. The theory is that block the reuptake of serotonin leaves more between synapses and this in turn can control mood or alleviate a negative mood. Is it really that simple?

Serotonin the brain’s mood modulator

Serotonin is associated with mood more than anything and particularly with alleviating depression and anxiety. But as with all things in the brain it is not quite so simple. Serotonin, or 5-hydroxytryptamine (5-HT), if you want to be technically correct, is known as a monoamine neurotransmitter. However, as Wikipedia put it “Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vasoconstriction.”

Serotonin is after all present in many parts of the body but of particular note is that of its role and production in the enteric nervous system, basically the gastrointestinal tract (digestive system). 90% of the body’s serotonin is produced in the GI tract a further 8 % is stored in platelets in the blood (which absorb this from the GI tract) and only 1-2% is present in the brain. However, the brain and body serotonin systems can be seen is separate systems with little to no influence on each other (the brain and body always exert some influence on each other).

In the body it has numerous functions but of interest is its role in wound healing one acting as a vasoconstrictor helping to close vein and arteries in wounds but also stimulating cell growth. Directly in the gut serotonin has an expellatory effect and can lead to diarrhoea- serotonin in present in many seeds which is why they also have a healthy effect on bowel movements. Interesting to note is also that serotonin is present in many insect and animal venoms, and this helps stimulate pain!

But back to our area of interest, the brain. What does serotonin do in the brain. Well, we have noted that it is considered the neurotransmitter related to mood. By mood we mean a general feeling of positivity and negativity rather than the ups and down of everyday life which may be more related to other transmitters such as dopamine. Hence its role in anti-anxiety drugs and that famous class of SSRIs such as Prozac. It is also negatively associated with aggression – that is lower levels lead to greater aggression. On closer inspection it is impulsive aggression that is increased rather than aggression in general. This I also noted in my feature article on love in last month’s issue whereby when in love serotonin levels decrease leading to mood swings and obsessive-compulsive behaviour.

Dopamine and serotonin pathways

Serotonin therefore seem to be a moderator more than anything in line with its roles as a general mood chemical or rather it takes the edge of impulsive or environmental swings. Its role though is still complex and further research has noted that of two tales of serotonin. This is better termed two receptors of serotonin as noted in a paper in 2017 by Carhart-Harris and Nutt. As I have noted previously neurotransmitters and modulators dock into receptors on neurons and it is this that triggers a response in the neuron. However, neurons have different types of receptors, and these can have different and sometimes opposing effects.

In the case of serotonin there are two receptors that seem to stimulate different pathways and responses. Type one receptors trigger a passive coping response to stress, i.e. moderating the impact of stress inputs, smoothing that curve of emotional stimuli, making the highs lower, and the lows higher. Type two receptors are responsible for active coping in response to stress by enhancing plasticity and learning. The latter has been less focused on in the literature and the general view of serotonin – but it is an important one, as in wound healing in the body whereby serotonin triggers receptors on cells to regenerate, this is also function of serotonin in the brain.

Now, I have said that serotonin in the body and serotonin in the brain can be considered separate systems. But as I also noted there are mutual influences on each other and particularly on the gut-brain axis as I have reported on in many other places. There has also been some interest of how to increase serotonin levels naturally – without pharmacological interventions. And these have some backing:

Mood induction: actively focusing on positive aspects and positive moods does lead to better moods and higher serotonin in the brain
Natural light: lack of natural light in known to be one of the major causes of Seasonal Affective Disorder – the winter blues. Light has multiple benefits and stimulates the brain in multiple ways. But bright natural daylight is associated with higher serotonin levels in the brain.
Exercise: this is again a general good health advice and exercise affects multiple pathways that I have also written about many times. But in this case, it also impacts serotonin and specifically through a precursor, tryptophan, an amino acid which is essential for the processing of proteins. This is elevated particularly when fatigued in the brain.
Diet: though many food stuffs contain serotonin such as bananas and many seeds these do not cross the blood-brain barrier. Similarly consuming foods high in tryptophan may not have an effect because they also elevate other amino acids and so serotonin synthesis is not elevated above other protein synthesis. However, some evidence points to milk but especially chickpeas and corn which improve the bioavailability of tryptophan and can hence increase serotonin synthesis.
Massage: in one study by Field et al. depressed pregnant women who received a massage twice a week from their partner, felt less anxious, less depressed, and had higher serotonin levels after 16 weeks.

So, to summarise serotonin is a key chemical transmitter in the human body and brain. In the brain it has a calming and moderating effect on stress moderating mood swings and keeping us in the positive. It also has a key adaptive function increasing plasticity and learning. Its synthesis can be elevated by doing those healthy things that we should be doing through multiple pathways and there appears to be a clear loop with mood. Daylight, exercise, nutrition, and positivity lead to higher serotonin levels which enables you to better manage the stresses of life avoiding a negative loop or vicious circle and also enhancing learning.

So, keep healthy for healthy brains. Obvious, right?

References

Kolb, B. & Whishaw, I. Q. (2009). Fundamentals of human neuropsychology: Sixth edition. New York, NY: Worth Publishers.

MacLean, P. D. (1990). The triune brain in evolution: Role in paleocerebral functions. New York: Plenum Press.

Singh, Vishram (2014). Textbook of Anatomy Head, Neck, and Brain ; Volume III (2nd ed.). p. 363. ISBN 9788131237274.

Haines, D; Mihailoff, G (2018). Fundamental Neuroscience for Basic and Clinical Applications (5th ed.). ISBN 9780323396325.

“Brainstem | Definition, Structure, & Function”. Encyclopedia Britannica.

“Cranial Nerve Nuclei and Brain Stem Circulation”. Neuroanatomy Online.

Exercise is Infectious

by Andy Habermacher | 2022 Mar 25 | Public, Quick Hits

Quick Hits
Daily brief research updates from the cognitive sciences

running crowd

This is an older study (2017) I came across and found fascinating. As many of you regular readers will know I have reported many times on the benefits of exercise. But this study was fascinating in that it looked at the contagion effect of exercise i.e. do people affect each other with the exercise bug?

To answer that question the researchers analyses data from a global network of 1.1 million runners over a period of five years and in addition 3.4 million social network ties. That’s a lot of data! What did they find?

Well, yes there is social contagion, runners do infect each other but the specifics are quite interesting. For example, it was found that both men and women influence men (men more than women) but that men do not influence women. Another interesting influence is that of being faster or slower runner. It was found that those who were slightly slower of faster influenced other most.

Read the paper for more interesting insights but of note is that exercise (in this case running) is infectious but how infectious depends on certain other factors such as closeness, gender, and how good you and your friends are – or not.

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Andy Habermacher

Andy is author of leading brains Review, Neuroleadership, and multiple other books. He has been intensively involved in writing and research into neuroleadership and is considered one of Europe’s leading experts. He is also a well-known public speaker speaking on the brain and human behaviour.

Andy is also a masters athlete (middle distance running) and competes regularly at international competitions (and holds a few national records in his age category).

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Reference

Aral, S., and Nicolaides, C. (2017).
Exercise contagion in a global social network.
Nat. Commun. 8.
doi:10.1038/ncomms14753.