The Neuroscience of Personal Space

We all have a need for personal space, the comfort zone we maintain around our bodies, implicitly entreating others not to encroach upon it.

In recent years researchers have been probing the ways in which we regulate this space, looking at how and why our brains tell us when someone is simply too close. These studies have meaningful, real-world implications. Not least, they are showing promise for helping those suffering from mental illness. As well as giving us better understandings of how our brains work generally, they are now also shedding light on the mechanisms of social dysfunction in patients with schizophrenia.

Among the new research tackling these problems is an ongoing study, by researchers at the Martinos Center for Biomedical Imaging at Massachusetts General Hospital, to develop an objective, quantitative means to measure what are known clinically as ‘negative’ symptoms. This is one of the great unmet needs in treating schizophrenia. When people think of the disease they tend to think of ‘positive’ symptoms like hallucinations and delusions, which have over the years come to dominate popular depictions and public perceptions of schizophrenia. But the negative symptoms, those that involve an impairment of motivation and action … these are in fact the most disabling.

Which is why the recent research is so invaluable. “An objective method would go a long way toward helping us find better treatments for these symptoms,” said Daphne Holt, a psychiatrist at Massachusetts General Hospital and an investigator in the Center. “The shocking reality is that, even after decades of intensive testing of potential novel treatments for negative symptoms, at the moment, there are no effective treatments available for them.”

Holt has been exploring a particular, often crippling aspect of these symptoms: social withdrawal. People typically understand this to mean not wanting to be around others, but it’s more than just that. Social withdrawal also involves an inability to read social cues or to understand the perspectives of others. As a result it can prove one of the most devastating components of the disease—especially because it can lead to the person having difficulty holding down a job, for example, or maintaining many relationships, the kinds of things we think of as part of having a normal, fulfilling life.

But what accounts for this? What gears and cogs in the brain are either turning or not turning to cause social withdrawal and its often debilitating effects? Researchers have a few ideas. Over the past several years Holt has been studying a model of social dysfunction in schizophrenia that proposes a relationship between this and very basic processes in the brain: sensory-motor functioning. One of the more prominent lines of thinking about schizophrenia today, the model suggests that many of the things we view as wrong with the higher cognitive functions are actually consequences of “lower” processes, like sensory-motor ones.

This is where personal space comes in.

In 2014 Holt and colleagues published a study looking at a particular sensory-motor circuit in the brains of healthy subjects using functional MRI. They found that the circuit displayed a specific type of response in the subjects, and that the response increased as objects appeared to “loom” toward them (as opposed to withdrawing from them). Notably, the experiments also showed that the responses were greatest when social stimuli like human faces were involved, suggesting a role for the circuit in basic social behaviors. Among them: the regulation of personal space.

Realizing the possible significance of this with respect to social dysfunction in schizophrenia, the researchers extended the study to explore the role the circuit plays in patients struggling with the disease. “We began these experiments because it has been well established that the size of personal space is abnormally enlarged in schizophrenia,” Holt said. “Consistent with this, our fMRI study found that the magnitude of responses of the ‘looming’ circuit to personal space intrusions in schizophrenia patients predicted the degree of personal space enlargement, as well as negative symptom severity, in these patients.”

The relationships they found—between looming stimuli, personal space regulation and negative symptoms—point to the important possibility that disruption of this basic sensory-motor circuit leads to abnormalities in non-verbal social communication, including personal space-related behaviors. If this proves to be the case, Holt and colleagues will have found something of a holy grail in the management of social dysfunction: a neural mechanism that can be specifically targeted by novel treatment approaches.

The researchers are now seeking to extend their findings, both by trying to understand better the normal functioning of the “looming” circuit and its role in a range of social processes and by working to determine which parts of the circuit are affected in schizophrenia—and which negative symptoms and social functions might be linked to these changes.

Gary Boas