My favorite passage from the chapter 4 talks about the limbic brain/system also referred to as the Paleomammalian brain. MacLean first came up with the term “limbic system” in 1952 to refer to the middle part of our brains. It can also be referred to as the old mammalian (intermediate) or the paleopallium brain. It matches with the brain of earlier mammals. What aroused my interest is the fact that the mature mammalian brain that resides in the limbic system is responsible for instincts and emotions, fighting, feeding, fleeing, and sexual behavior as well. As MacLean thinks, every action in this emotional system can either be agreeable or disagreeable. I also noted that endurance is dependent on evasion of pain and reverberation of pleasure. A number of emotions including rage, fear, pain, pleasure, and joy are produced when the limbic system of the brain is aroused with a mild electric current. No emotion has been discovered to exist in one place for a long time.
However, the entire limbic system appears to be the main source of attention, emotion, and affective memories. Physiologically, it comprises thee amygdala, hippocampus, and hypothalamus. It aids to establish salience and valence, creative behavior, and unpredictability. Salience in Buddhism is known as vedena, which means “feeling”. An example is when you feel positivity or negativity towards something. Salience, on the other hand, refers to situations that get your attention. The limbic system has wide interconnection with the neocortex; thus the brain functions are not purely cortical or purely limbic but a mixture of the two.
Maclean discovered in the limbic system a corporeal basis for the paranoid and dogmatic tendency, the biological basis for the thinking tendency to be subsidiary feeling, to downsize desires. He sees an immense danger in the limbic system power. According to his understanding, such lowly mammalian brain synonymous with the limbic system appears to be the core of our value judgments and not the somehow advanced neocortex. The limbic system decides whether the human higher brain has a good scheme or not, whether it feels correct or true.
It is exciting to note that the same structures present in the human limbic system are also present in the brains of ancient animals like the alligator. The limbic system of alligator is deeply involved in smell. It plays a crucial role in hunting prey, eating it, and defending territory. The limbic system of humans is more concerned with emotional behaviors and motivation. Structures in this part of the brain intersect; however, research has indicated that the amygdala and the hippocampus appear to be the main parts responsible for emotions. The amygdala links up with the hippocampus and the thalamus. Such a connection enables it to take part in the control and mediation of main activities like love, friendship and affection, and mood expression.
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It has been pointed out that the hypothalamus, especially the median part, has been discovered as a main provider to the production of loud and uncontrollable laughter. The Basal Ganglia, also a part of the limbic system, plays a crucial role in development and coordinating posture and motor movements. Complex neural connections tie the Cerebral Cortex to Basal Ganglia. The main effect of the Basal Ganglia is to prevent unwarranted muscular activity. Disorders of the Basal Ganglia end in exaggerated and uncontrolled movements.
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