What if psychopathic behavior stems from a surprisingly basic physical glitch?

A recent review article suggests that psychopathy is related to dysfunction in the brain systems responsible for sensing and regulating the internal physical state of the body. The findings provide evidence that impaired bodily regulation may contribute to the hallmark emotional and behavioral traits of the disorder. This research was published in the journal Aggression and Violent Behavior.

Philip Deming, a postdoctoral fellow at Northeastern University, and Clare Shaffer, a graduate student at Northeastern University who will soon transition to a postdoctoral role at Massachusetts General Hospital, wanted to approach the study of psychopathy from an evolutionary, body-centered perspective. The financial and emotional toll of the disorder motivated their research.

“We want to understand the brain mechanisms of psychopathy because the disorder has a terrible impact on society,” said Deming. “Psychopathic people often steal, cheat, exploit, and victimize other people, costing the US hundreds of billions of dollars each year and causing real suffering.”

Because current science lacks proper treatments for these behaviors, the researchers turned to the brain for answers. However, they noticed that past attempts to map psychopathy often started by looking at a specific behavioral symptom, like a lack of empathy, and then tried to find a matching brain signature.

“The trick is that we approached this question from a somewhat unusual starting point,” Deming explained. “In the past, scientists have started by looking at human behavior and studying how the brain enacts those behaviors. We see people experiencing emotions or empathizing with other people, so scientists would study how the brain ‘does’ emotion or empathy.”

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Instead, Deming and Shaffer took a deductive route, starting with the brain’s fundamental evolutionary purpose.

“We started from the question: ‘What is a brain for?’” Deming said. “If you look at our evolutionary history, then the answer seems to be this: the brain is for regulating the internal organs of the body (the heart, lungs, gut, and so on).”

Evolutionary biology suggests that brains developed to anticipate and meet the metabolic needs of the body before those needs actually arise. This preventative, highly efficient regulatory process is known as allostasis. To coordinate the organs, the brain must constantly monitor the internal physical conditions of the organs, such as heart rate, digestion, and breathing. The brain’s ability to sense these internal physical states is called interoception.

“To coordinate the organs, the brain has to sense them. These processes are called allostasis and interoception, so we call this an ‘allostatic-interoceptive view’ of the brain,” Deming noted. “Once we take this view, new questions and new answers emerge about what might be happening in the brains of psychopathic people.”

These complementary functions rely on the allostatic-interoceptive system, which spans multiple brainstem regions, subcortical structures, and large-scale neural networks. Signals from the body travel up to the brain through two primary pathways. One pathway is the vagus nerve, which runs from the abdomen up the front of the neck. The other pathway is the spinal cord, which carries sensory information from various internal organs up into the brainstem.

Once these signals reach the brainstem, they are distributed to various subcortical and cortical regions. The brain continuously uses this incoming information to fine-tune ongoing cognitive processes and adjust bodily functions. This dynamic indicates that a person’s heartbeat or breathing pattern can directly influence how they perceive the world around them.

To explore this concept, the researchers synthesized existing evidence from a wide array of published neuroimaging studies on psychopathy. They examined data from structural imaging, which looks at the physical wiring of the brain, as well as functional imaging, which tracks blood flow and brain activity over time. The synthesis included meta-analyses, which are large mathematical reviews that combine data from dozens of previous brain scans.

“Psychopathy might be a disorder of sensing and regulating the body’s organ systems,” Deming said. “When we looked across 20-plus years’ worth of MRI studies, brain differences kept popping up within the ‘allostatic-interoceptive system.’ This is a widespread brain system that plays a central role in sensing and regulating the body.”

The authors reviewed studies involving community members as well as forensic populations, such as people in prisons. They specifically looked at fractional anisotropy, a metric used to measure the structural health of white matter tracts. White matter serves as the physical cabling that connects different brain regions, allowing them to communicate rapidly.

“In psychopathy, this system appears to have degraded white matter pathways,” Deming explained. “It also interacts with other brain networks differently. And it shows different patterns of activity when psychopathic people are focusing on a task like empathizing with another person.”

Specifically, the uncinate fasciculus and the cingulum show signs of degradation. These neural pathways link the emotional centers of the brain to the areas responsible for high-level decision-making and bodily regulation.

“The root problem might not be one of empathy or emotion but of something more fundamental,” Deming said. “The root problem might be in how the brain manages the heart, lungs, and other organs and prepares them to meet the demands of the current context.”

In addition to physical wiring differences, the scientists found evidence of altered functional connectivity. Functional connectivity refers to how well different areas of the brain activate together and share information during rest or active tasks. The data indicates that people with psychopathy show reduced communication between the cortex and deeper brain structures like the amygdala.

When the brain cannot properly share information between these areas, the resulting regulatory signals lack rich contextual details. The authors propose that this impairment leads to a highly context-insensitive way of regulating the body. During cognitively demanding tasks, people with psychopathy also display unusual patterns of brain activation.

Because of these altered patterns, people with psychopathy often show lower skin conductance and heart rate responses when anticipating a stressful event, such as a mild electric shock. They also tend to display abnormal hormonal regulation in response to social stressors. People with psychopathy frequently exhibit unusually high baseline levels of testosterone and oxytocin, alongside blunted cortisol responses during stressful situations.

The researchers suggest that these impoverished regulatory signals may hinder a person’s ability to allocate attention to important environmental cues. If the brain fails to properly integrate internal bodily signals with external sensory information, it struggles to identify what is actually important for survival. This failure might explain why people with psychopathy selectively focus on certain cues while entirely disregarding threats.

Taking this body-centered view also helps clarify decades of fragmented research. Historically, different scientists have proposed different core deficits for psychopathy, ranging from poor attention to a lack of fear.

“It was surprising to see how this theory might weave together previous theories about psychopathy,” Deming told PsyPost. “Scientists tend to think of these previous theories as being distant and disconnected from one another; they don’t predict or explain the same phenomena.”

Rather than seeing these older ideas as entirely separate, the researchers believe a focus on bodily regulation connects them.

“But I think most of those theories can be easily folded into our view, which says that the problem is in how the brain is sensing and regulating the body,” Deming continued. “This process is central to emotional experience, drives attention, and heavily involves the autonomic nervous system, all of which have been pointed to by prior theories as the central problem in psychopathy.”

It is important to recognize the potential misinterpretations and limitations of this theoretical framework. The model relies heavily on indirect spatial associations between past brain imaging results and known regulatory networks.

“The big caveat is that MRI findings in relation to psychopathy are all over the map,” Deming said. “Although we found some recurring findings in brain regions that are important for sensing and regulating the body, studies usually fail to replicate one another.”

Because of natural biological flexibility, a single behavioral trait might look completely different in the brain scans of two different individuals.

“One study will find lower activity in region A, while another study will find the opposite, higher activity in region A, along with lower activity in region B,” Deming explained. “Our field needs to grapple with these inconsistencies.”

To explain why previous brain imaging studies of psychopathy have been so inconsistent, Deming and Shaffer introduced two concepts.

“And while some scientists in the field point to methodological differences between studies, we proposed two new ideas in the field,” Deming said. “First, inconsistent findings could result from core dysfunction in the allostatic-interoceptive system.”

The regions managing bodily regulation sit at the very top of a neural processing hierarchy. A disruption at this high level can alter activity in many downstream sensory regions, creating the illusion of scattered, inconsistent brain abnormalities across different studies.

“This is a possibility, supported in part by a recent study from Dugré and De Brito, since this system can change activity throughout the brain depending on the current context of the body in the world,” Deming noted.

The scientists also introduced a concept called degeneracy, which is an organizing principle in biology meaning that different brain structures can achieve the exact same functional outcome.

“Second, and relatedly, brain function differs across contexts (this is called degeneracy),” he continued. “Basically, we probably shouldn’t expect findings to replicate when we’re averaging across people and across instances, and instead we should be studying individual brains regulating individual bodies in context.”

Moving forward, the scientists recommend shifting away from group-average studies and moving toward precision psychiatry. This approach involves deeply tracking individual patients across many different contexts to see how their specific brain and body interact.

“The next step is to more deeply probe how the brains of psychopathic people are sensing and regulating their bodies,” Deming said. “This is a process few studies have studied in a targeted way, and those studies mostly focused on how people perceive their heartbeat consciously.”

Researchers might test these regulatory mechanisms directly by safely manipulating a person’s internal physical signals. This could involve stimulating the vagus nerve or using ingestible vibrating capsules to alter sensations in the gut.

“But there are somewhat more hidden processes we should also be studying,” Deming explained. “For example, how do their brains integrate bodily signals with signals arriving to the eyes and ears? If we slightly alter what is happening in their heart and lungs, can we change how they process social information?”

Advancements in ultra-high field magnetic resonance imaging will likely aid these future studies by allowing scientists to see incredibly small structures in the brainstem.

“We can also start using more powerful MRI scanners to better image the small brain structures that make up the allostatic-interoceptive system,” Deming added.

Currently, there is a severe lack of evidence-based treatments that target the biological roots of psychopathy. However, interventions that directly address internal sensing, such as specific biofeedback therapies, have shown some early promise. In biofeedback training, patients observe real-time monitors of their own heart rate or brain waves and practice volitionally controlling them.

Some past biofeedback studies have successfully trained individuals with psychopathy to regulate specific brain regions connected to the allostatic network. These early interventions appeared to reduce aggressive and impulsive behaviors. By combining detailed imaging with targeted biofeedback therapies, clinicians might eventually develop personalized treatments that train patients to better monitor and regulate their internal states.

The study, “Brain evidence of allostatic and interoceptive dysfunction in psychopathy,” was authored by Philip Deming and Clare Shaffer.