Welcome to the Limbic system!



Reading a wonderful article by Emily Joshu in a special edition from Time magazine (4) I found myself reminiscing over the lectures from my undergraduate and my current MSc which led me to reflect on my upcoming new role working with people experiencing cognitive decline. Joshu’s piece motivated me to revisit my slides and gloss over what I have learned and how this knowledge may help me when assisting people through activities that aim to support emotional health and wellbeing. As such I thought it would be nice to use Joshu's article as a template to revist the limbic system and share this exercise with you. Afterall, learning new information is essential for brain health!

So, welcome to the Limbic system!

The exact neural structures which make up the limbic system are still debated (1), however what is agreed is that it is made up of intertwined brain regions located in the medial portion of the brain (2). The circuit navigates as part of the limbic system and influences emotion, memory, spatial processes, and reward. So this is the system that is responsible for motivating our behaviours and our want for things like food and sex. When we get those ‘wants’ the limbic system releases endorphins which leave us with a sense of contentment – our ‘reward’! (3). Furthermore, this region of brain structures influences our emotions and drives our learning processes. Interestingly, the present evidence indicates the functions of the limbic system supports memory (more than emotion) (2).


So, let’s look at snippets of information about the specific areas believed to bolster what we understand is the limbic system.

Hippocampus.


Hippocampus is an important part of the forebrain structure and is where our memory is said to begin and be processed. Its shape is similar to a seahorse and it is seated within the temporal lobe. It is also the seat of our sensory experiences such as touch, taste, smell, sound and sight (1).


Takeaway from the hippocampus = at Christmas you may remember the smell of your roast lunch cooking or the aroma of a mulled wine…it is the hippocampus that is believed to correlate this sense to a memory!





Amygdala

(I called this area Amy-ig-dala, for long time! I hold my dyslexia responsible and the fact that the first three letters are my name! It has taken some time to re-learn how to pronounce the word (“Amig-dala” for those who are curious to know!)

The Amygdala (named from Greek origin as it is shaped like a (teeny-weeny) almond!) is also located in the temporal lobe near to the hippocampus and is part of the cingulate cortex, and acts as a connection from the hypothalamus to other brain areas (3). The amygdala is believed to influence emotion, also retaining useful memory about a behaviour and then connects to the prefrontal cortex to elicit a response, particularly in the search for ‘reward’ (3,4). Looking at the prefrontal cortex (more concerned with consequences), we can see where things go awry if it is damaged, OR it has yet to develop (*note for parents/carers of teens = I will write about prefrontal development another time!) the decisions of what behaviours are appropriate may not seen as such in the eyes of wider society or indeed, for the persons own well-being.










Takeaway from the Amygdala = We may have all experienced a moment of reasoning which seems less than reasonable. Hello amygdala…very broadly speaking can be seen as the linkage between the ‘moment’ to the ‘consequence’. That is over simplified, but is just a simple way to remember part of its role!

Prefrontal Cortex

Much as it its name suggests, the prefrontal cortex is located in the frontal lobe (in front of the central sulcus) and influences motor actions, working memory, decision-making and inhibits lower brain regions (personality and behaviour) (2,3,4). As such, this section of our brain assists us by processing our emotional experiences in a way which is appropriate and results in behaviour that is also (2).


Takeaway from the Prefrontal Cortex = Have you experienced moments where you feel governed by your emotions? Have you felt that you simply can’t plan? unable to look at the future? Don’t seem able to consider the consequences of your behaviours or actions? Hello Prefrontal Cortex!

Olfactory Cortex

Where has our motivation evolved from? Right here in the olfactory system! Regarded as one of our most primitive regions the olfactory cortex is responsible for processing our sense of taste and smell (3). Our sense of smell governs many of our actions, right from drawing us towards smelling beautiful flowers or selecting an intimate partner, our sense of smell is king! The olfactory bulb produces an electrical signal which causes a response in the olfactory cortex which then go to the prefrontal lobe eliciting a response either ‘rewarding’ or otherwise, which in turn influences our behaviour accordingly (3,4).



Ancient Greeks believed that nerves operated as passages carrying tiny bits of the stimulus into the brain to be recognised! However, I don’t like to consider this theory if I am near somebody who has flatulence!



Take away from the olfactory cortex = Smelling motivates much of our behaviour, so be mindful of this when walking past a ice-cream van for the fourth time in one afternoon or siting yourself closer to somebody on the train!

Hypothalamus

Hot, cold, hungry, need the toilet, ovulating? The hypothalamus influences various functions, many on a cellular level beyond our conscious control or even awareness (3). The hypothalamus is a key structure located in the forebrain and not only does it participate in motivating our actions and behaviours it also controls the release of stress and sex hormones (2,3,4). Moreover, according to Papez’s circuit (5) the hypothalamus elicits intrinsic feelings particularly emotional experiences which supports why the hypothalamus has earned the name ‘Command centre’ (3).


Takeaway from the hypothalamus = activates hormonal and cardiovascular responses and reminds us when we need to eat, drink or even when we need to sleep (amongst other things like regulating bodily functions).

Overall Takeaway = The functioning of the brain is amazingly complex. Despite our human ‘need’ to know everything there is to know about all things, the brain reminds us that its intricate workings go far beyond a simple explanation. No one section of the brain has a single function, nor do neighbouring areas of cortex which reside in separate lobes have functions that are distinct from each other!

I hope that you have found this as interesting as I do! I am only offering little snippets of information and am pleased to discuss them with you! I urge you to read from Emily Joshu’s article (4) and indeed Professor Susan Greenfield’s book (3) to read some interesting and accessible information about the limbic system and the brain as a whole structure (or the sum parts of it!).




With thanks to all the resources I have cited and images I have used!

References

1. LeDoux, J. E. (2000). Emotion circuits in the brain. Annual Review of Neuroscience, 23, 155-184.

2. Feinstein, J. S. (2012). Examination of the limbic system's role in emotional experience using a human lesion model.

3. Greenfield, S., & Bacon, G. (Eds.). (1999). Brainpower: Working Out the Human Mind. Element Books Limited.

4. Joshu, E. (2018). Understanding the limbic system. The Science of Memory: The Story of our lives. (Special Edition), 14-15.

Images

Seahorse Photo by David Clode on Unsplash

Almond Photo by Valentin Salja on Unsplash

Smelling flowers Photo by Samantha Gades on Unsplash

Taste Photo by Nathan Hanna on Unsplash

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