How Placebo Effects Work to Change Our Biology & Psychology

The episode opens by grouping three phenomena: placebo effects, nocebo effects and belief effects. All three are framed as products of the brain's ability to place an expectation on what is about to happen and, in doing so, to change what actually happens, independent of the physical and chemical properties of a drug or other treatment. The conditions named as examples include pain, Parkinson's disease, irritable bowel syndrome, asthma and stress. The host's central claim is that, although these effects can look purely psychological, "it's not that at all."

The argument is that expectation changes physiology itself. The host describes neural circuits dedicated to linking expectation with core functions such as heart rate, blood pressure and the release of neuromodulators like dopamine and adrenaline. He acknowledges that placebo controls remain vital in certain clinical studies, but says placebo, nocebo and belief effects also have powerful physiological effects separate from that role. He adds that several highly esteemed medical researchers believe these effects should be leveraged as treatments in their own right.

Working definitions given in the episode: - Placebo effect: an inert substance or behavioral treatment, one that "shouldn't do anything on its own," somehow improves symptoms or performance. - Nocebo effect: an inert drug or behavioral intervention that instead worsens symptoms or performance. - Belief effect: learning specific knowledge changes your expectation about what will happen, for example in relation to stress, a food, a drug or a behavioral protocol, and that information leads to the specific outcome.

The host notes that people rarely separate placebo from nocebo, and that he will mostly use "placebo effects" as shorthand. He treats belief effects as closely related, with "placebo" usually reserved for drugs and behavioral interventions, and "belief effects" used more specifically for cases where information of any kind changes a physiological or psychological outcome. What ties all three together is that they work by changing expectation, which places them in the nervous system, specifically in the brain's prefrontal cortex.

The prefrontal cortex is described as the neurons and connections just behind the forehead, divided into many subregions. Its overall function is characterized as the ability to activate or suppress neural circuits deeper in the brain. Citing a neurosurgeon who was a previous guest, the host says the region can be thought of as controlling other brain structures by saying "Shh," that is, by suppressing them, as when it suppresses an impulse to move or to shout.

To illustrate, he uses the common experience of standing at a cliff edge or on a high bridge and having the spontaneous thought of jumping. He reads this not as a death wish but as the prefrontal cortex evaluating context and predicting how bad the outcome would be. Having the thought briefly, recognizing it as dangerous, and not acting on it is presented as evidence that the prefrontal cortex is working properly. He repeatedly cautions listeners not to engage in the action.

The prefrontal cortex being largely a context evaluating and prediction machine is essentially looking at that landscape and predicting what would happen

The broader theme for the episode is that the prefrontal cortex is an expectation- or prediction-making machine, constantly evaluating context: what is going on in a room or scene, what is supposed to happen, and what one should or should not do. The host adds that some subregions have "labeled line" communication, a dedicated highway to brain areas that control bodily functions such as heart rate and blood pressure. He previews a paper, which he calls one of his favorites, that identifies a prefrontal region controlling primitive functions like body temperature and heart rate in relation to beliefs or social scenes. He contrasts this with how cold water or other physical stressors raise heart rate or cause vasoconstriction.

In this account, placebo, nocebo and belief effects begin with information, such as a label, a doctor or a scientist saying a pill or injection will do something, or something learned about a drug, supplement or protocol. That information creates an expectation. Prefrontal circuits then activate deeper and evolutionarily ancient structures such as the hypothalamus, which the host says is well conserved across mammals and even reptiles, as well as brainstem areas that control functions like breathing. The prefrontal cortex is said to combine present context, memories and future goals into signals to systems governing immunity, stress, reward and pleasure, so that "our physiology of our brain and body fundamentally changes such that those things happen."

Before turning to studies, the host names his main source: "Placebo Effects: Understanding the Other Side of Medical Care" by Fabrizio Benedetti. He says he used it prominently in researching the episode and will draw several examples from it. He also discloses that he has never met the author and has no relationship with the publisher or the book beyond admiring it.