The Limbic System – Creator of Emotion

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The limbic system, also known as the paleo mammalian cortex, is a compound system in the brain consisting of several vital areas (including the hippocampus, thalamus, hypothalamus, the ventral tegmental area, and the cingulate gyrus). In conjunction with these structures are the amygdalae, which serve as an ‘entry point’ to the limbic system. The system works coherently to manage three key functions: emotion, memory, and arousal (also known as stimulation). It is widely thought to have originated and developed from the ‘once-primitive’ mammalian brain as a result of evolution, because of its primary handling of mammalian instincts rather than learned or acquired behaviour. Located both within the forebrain and the midbrain, the associated structures of the limbic system form an intricate network. These structures are found on either side of the thalamus (which relays motor/sensory information to the cerebral cortex), right beneath the temporal lobes. This system is ‘contained’ within the cerebrum, forming one of the innermost structures, hence why it is linked to the early mammalian brain (with the outer structures having developed over time through evolution).1

As previously mentioned, the amygdalae serve as the ‘entrance’ to the limbic system and as the main emotion centre of our brains. These two almond-shaped bundles of neurones are situated near the end of the hippocampus, either side of the thalamus. The amygdalae receive incoming sensory signals from our body, transferring these signals into emotional responses (such as sadness, anger and fear). Additionally, the amygdalae are essential in a process called ‘memory consolidation’, whereby recent stimuli/memories are transformed into long-term memories, hence allowing recognition of such stimuli in the future. It is also thought that the amygdalae can form ‘pathways’ that link them to the visual and auditory centres of our brain, allowing new emotional perceptions to be established. For example, ‘pathways’ between the amygdalae and the primary visual cortex could mean that hallucinatory responses are elicited from certain epileptic seizures.  Another structural part of the limbic system is the hippocampus – two horn-shaped parts of the brain that curve back from the amygdalae. This structure is responsible for the creation of new memories, and their subsequent transformation into long-term memories. This is why, when the hippocampus is damaged, the victim usually loses the ability to form new memories whilst older memories are unaffected.2  

Just below the thalamus is one of the most important parts of the limbic system (and the brain in general) called the hypothalamus. Being a hugely active part of the brain, the hypothalamus is concerned with the process of homeostasis (maintaining a constant internal/bodily environment), as well as the adjustment of the body’s response to hunger, pleasure, aggressive behaviour etc… This structure transmits electrical instructions to the rest of our bodies in two ways. It does this firstly through the autonomic/subconscious nervous system, allowing it to control sympathetic and parasympathetic nervous functions, and secondly via the pituitary gland (an endocrine gland that acts to store and release hormones required by the body). The hypothalamus is intimately connected with the pituitary, hence it can also regulate the amounts of hormones produced and secreted by this gland. As it plays several essential roles within the body, damage or disruption to the hypothalamus can cause severe disorders, for example to do with growth, emotion, sleep and body temperature regulation. 3

The four more minor parts of the limbic system still play a crucial role in our emotional function. These include: the cingulate gyrus (responsible for emotionally significant events, and linking memories to pain and smell), the ventral tegmental area (responsible for pleasure through its constitution of dopamine pathways – damage to this structure means victims can’t usually feel pleasure, so often turn to drugs, alcohol etc.), the basal ganglia (responsible for repetitive habits, focusing attention, and ‘reward experiences’), and finally the prefrontal cortex (which not only contains dopamine pathways for pleasure, but is also involved in making plans and considering the future).4

Due to the finely interconnected nature of the structures within the limbic system, problems with stress or rare diseases (for example paraneoplastic limbic encephalitis, a neurological syndrome that can arise from brain tumours) usually affect the whole system. In order to maintain the normal function everyday activities should be carried out, which include regular exercise and meditation. Additionally, certain homeopathic treatments like aromatherapy are useful, as they provide structures such as the hippocampus with essential oils and have a relaxing effect on our nervous system – helping us to keep our limbic system in-check.

References

  1. Boeree, C.G. (2009), The Emotional Nervous System. [online] Last accessed 6 April 2020: https://webspace.ship.edu/cgboer/limbicsystem.html 
  2. Good Therapy (n.d.), Amygdala, [online] Last accessed 6 April 2020: https://www.goodtherapy.org/blog/psychpedia/amygdala 
  3. Hypothalamus (2020) Wikimedia Commons, [online] Last accessed 6 April 2020: https://en.wikipedia.org/wiki/Hypothalamus 
  4. Boeree, C.G. (2009), The Emotional Nervous System. [online] Last accessed 6 April 2020: https://webspace.ship.edu/cgboer/limbicsystem.html 

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