Reptilian Brain (Instinctive Brain)
Man as a triune being
In the 1970s, Paul D. MacLean, an American physician and neuroscientist, developed a model of brain structure and evolution, describing it as “Triune Brain” because he identified three main anatomical and functional formations that overlapped and integrated throughout evolution. He named these formations the reptilian brain, ancient mammalian (Limbic System), and recent mammalian (Neocortex). While this division is now considered a simplification, it helps to better understand brain development and explain how the rational part relates to the more primitive and aggressive part.
From a pedagogical perspective, we can read together a page by Patrizio Paoletti that illustrates the possibilities of human development from the perspective of triune brain development: “Humans have a remarkable triune brain structure, as it simultaneously highlights a line of continuity and a line of innovation in the long history of species evolution. On one hand, this brain structure ‘roots’ humans in the phylogenetic adventure of life that began in immemorial times; on the other, it ‘elevates’ them as the highest result of this ancient and unstoppable evolutionary race toward continuous improvement. Humans, therefore, belong to the family of living species but are, at the same time, sui generis, possessing a unique brain structure with extraordinary and perhaps still unimaginable potential” (Paoletti, 2008, pp.15-16). In this glossary entry, we explore the oldest part of our brain, the reptilian-instinctive brain.
Structure and functions of the reptilian brain
The reptilian brain, also known as the instinctive brain, represents a fundamental part of the central nervous system present in humans and many other animals. It is named because it is an evolution of the reptile brain and refers to the most primitive and ancient part of the human brain, responsible for basic behaviors and instincts essential for survival. The reptilian brain is composed of key anatomical areas, including the brainstem, cerebellumThe cerebellum is a structure composed of two symmetrical ce... More, and hypothalamus. The brainstem began evolving more than 500 million years ago. It connects the brain to the spinal cord and controls vital functions such as breathing, heartbeat, body temperature, and digestion. The cerebellum is attached to the back of the brainstem and mainly manages body posture and the coordination of muscle movements. The hypothalamus regulates body homeostasis, controlling functions such as hunger, thirst, sexual desire, and circadian rhythm.
Role of the reptilian brain in our behavior
Although this brain is often considered primitive compared to other brain parts, it is important to emphasize that the three brain areas are closely interconnected and work together to integrate cognitive and emotional functions: while the reptilian brain primarily manages – as we have seen – instinctive and automatic responses, the limbic brain adds an emotional component to these responses, and the cerebral cortex – particularly its most recent part, the neocortex – is involved in rational thinking, planning, and processing complex information. Overall, human behavior is influenced by multiple factors, including higher cognitive processes derived from the limbic brain and neocortex.
These brain regions allow humans to make conscious decisions, process complex information, empathize, and plan for the future. However, in situations of extreme stressWhat is stress? From a clinical perspective, stress is a phy... More or imminent danger (real or perceived), the reptilian brain can override higher brain functions, leading to a fight-or-flight reaction. This means that primordial instincts can override rational thought under certain circumstances. For example, when a person faces immediate danger, they may react instinctively without thinking, such as quickly moving away from a burning object or reacting with an instinctive defensive attack.
Beyond these extreme situations, it is essential to understand that the reptilian brain can also subtly influence our behaviors and reactions. For example, our instincts may push us toward protective behavior, territoriality, or resource-seeking. Recognizing these instincts can help us better understand the reasons behind our actions and adopt a more conscious approach in managing situations.
The reptilian brain in human communication
What kinds of messages trigger the reptilian brain? Communication theory and marketing have studied various triggers that make this brain prevail over all others, making our behavior compulsive. For example, greed and aggression are some of the primordial emotions of the reptilian brain: these are triggered by the prospect of gaining or losing money, power, or social status. Other primordial emotions of the reptilian brain include self-preservation, dominance, obsession, and compulsion. In this case, the stimulus is anything that allows us to gain or lose in relation to the attractiveness of our appearance or social symbols. Another powerful reptilian brain trigger is food, one of the necessities we need every day. Because the reptilian brain evolved to keep the body alive and meet our genes’ needs, food is a very powerful trigger, capable of generating greed, aggression, obsessive, and compulsive behavioral responses from the reptilian brain.
Especially when food is scarce, this reptilian brain trigger will make us behave like animals whose only concern is survival. Consider how these instinctive needs are daily exploited by online news or advertising to determine our choices!
From a complementary perspective, we can say that the reptilian brain allows us to enjoy bodily existence, the pleasure of human experience, expressing vitality and appreciation for life.
