Reevaluating the concept of health: Allostasis vs. Homeostasis Neuroscientist Peter Sterling challenges the traditional concept of homeostasis and introduces the concept of allostasis, which focuses on the body’s active adaptation to internal and external changes. This concept, proposed in the late 1970s, suggests that health is not just about maintaining internal parameters but also involves the body’s proactive response to environmental stressors. Sterling’s interview reveals that this idea is not commonly taught in medical education, despite its potential significance in understanding human health and physiology. Transcript: Speaker 1 There will be a link to this in the show notes. Today, I’m going to be sharing the work of neuroscientist Peter Sterling. Dr. Sterling spent his career teaching medical students and exploring the function of the retina. He has written two fascinating books, principles of neural design and what is health. We recorded an interview that focuses on his new book, What is Health, Allostasis, and the Evolution of Human Design. Unfortunately, the sound quality was very poor and due to time constraints on my end, I was unable to schedule another recording. So I’m going to share the key ideas with you today along with a few excerpts from our conversation. Let’s start with the word Allostasis. I can tell you from my first hand experience as a physician that this is not a concept that students in physiology or medicine are being taught, even though Dr. Sterling first proposed the idea in the late 1970s. We’re talking about homeostasis, which is the idea that health depends on keeping a large number of parameters within an acceptable range, like a thermostat. However, Sterling argues convincingly, I think, that this is an inadequate model of what’s really going on. (Time 0:02:31)
Redefining Health and Homeostasis Homeostasis, the concept of maintaining parameters within an acceptable range, is challenged by the idea of allostasis, which involves the brain predicting the body’s needs. This challenges the traditional understanding of health and suggests that the brain is crucial not just for our experience of the world, but also for our survival and health. Transcript: Speaker 1 We’re talking about homeostasis, which is the idea that health depends on keeping a large number of parameters within an acceptable range, like a thermostat. However, Sterling argues convincingly, I think, that this is an inadequate model of what’s really going on. One reason for this, as mentioned in the opening quote, is that the knees of the body are constantly changing. Allostasis includes the idea that the brain tries to predict what the body will need. This will seem obvious to long-term listeners, since many of my guests have talked about the predictive properties of the brain. But before we explore that idea, I want to address the question I can imagine some of you have. Why does it matter? Why should I care about this? This brings us back to the title of Sterling’s book, What is Health? Once we explore the evidence that supports Sterling’s viewpoint about allostasis, we will examine its implications for our understanding of health and disease. What does this have to do with brain science? The brain doesn’t just create our experience of the world, it is the key to our survival and health. (Time 0:03:37)
Evolutionary Development and the Role of Dopamine Bilaterally symmetrical organisms appeared around 500 million years ago, leading to arthropods and vertebrates which bequeathed 93% of our proteins, including dopamine. C. elegans, a simple worm with 302 neurons, uses dopamine as a reward signal. The mechanisms of rewarding behavior with dopamine have been present for half a billion years. As biological systems become more complex, homeostatic mechanisms become more energy-expensive. Transcript: Speaker 1 One key evolutionary development that Sterling emphasized was the appearance of bilaterally symmetrical organisms around 500 million years ago, in particular bilateral worms That led to arthropods and vertebrates. This ancestor bequeathed us 93% of our proteins, including key transcription factors, transmitters, neuro modulators, including dopamine. During the interview, we talked about C. Elegans, that famous simple flat worm with its only 302 neurons. C. Elegans uses dopamine as a reward signal. So the key idea is that the mechanisms of rewarding behavior with a small surge of dopamine, that’s been with us for half a billion years. Well, you might be thinking, well, how does this get us from homeostasis to allostasis or predictive control? There are numerous pathways in the body that are regulated by homeostatic mechanisms. But the key idea is that as biological systems become more complex, homeostatic mechanisms waste energy, and energy is expensive. (Time 0:07:55)
The Transition from Homeostasis to Allostasis and Predictive Control As biological systems become more complex, they transition from using homeostatic mechanisms to allostasis or predictive control. Homeostasis is used when there is a critical link in the chain lacking reserve capacity, while predictive control is an initial strategy that may make false predictions in rapidly changing conditions. Homeostasis provides rapid, precise corrections, while allostasis predicts, showing that both are essential for survival. Transcript: Speaker 1 Well, you might be thinking, well, how does this get us from homeostasis to allostasis or predictive control? There are numerous pathways in the body that are regulated by homeostatic mechanisms. But the key idea is that as biological systems become more complex, homeostatic mechanisms waste energy, and energy is expensive. So it appears that the design principle is to use homeostasis when there’s a critical link in the chain that lacks any reserve capacity, an essential bit. So auto regulation emerged in the first eukaryote cells. A good example of a critical link in the chain would be cardiac cells. They have to keep on beating, whereas other cells in the body might, quote, choose to be less active when the energy is low. Predictive control is an official initial strategy, but in rapidly changing conditions, it could make false predictions. So we need homeostasis to provide rapid precise corrections. Regulation is not about defending fixed parameters. Allostasis predicts, while homeostasis, corrects. Thus, they’re both essential for survival. (Time 0:08:47)