Get out of my personal s p a c e

Posted by Jess Du on May 21, 2020 in Behavioral Neuroscience, Mental Illness, Perception, Uncategorized | Leave a comment

Social distancing has been a key part of the response to the coronavirus pandemic, and for many people it’s the most pressing reminder of the crisis. One thing I’ve noticed as I’ve been adjusting to social distancing in the past few months is a changing sense of personal space. For example, when I go outside for a run or walk in my neighborhood, sometimes I’ll spot someone walking towards me on the same sidewalk. Even though they may be 20 or even 30 feet away, well out of my usual personal space boundary, I feel alert all of the sudden, like the diaphanous bubbles of personal space surrounding us are quivering towards each other.

Personal space has been defined in neuroscience research as a space around an individual where intrusions can cause discomfort (1). Each individual tries to minimize discomfort by maintaining a distance from others, but the process of maintaining personal space is dynamic, depending on the environment, social context, the identity of the other individuals, and past experience. Squeezing next to strangers in a packed subway car might be mildly uncomfortable, but if a stranger stood right next to you in an empty subway car it’d probably feel even more uncomfortable, even though the volume of intrusion on your personal space is smaller. Conversely, if that person were your friend, it would feel natural for them to be close. Most of us are able to maintain a socially acceptable distance from other people and adjust according to context effortlessly, but it is actually a computationally complex task that requires integrating a variety of contextual cues and is shaped by cultural learning. So how does the brain dynamically represent our personal space? Turns out, digging into this question could bring researchers insights into not only how we interact with the world, but also how we navigate social interactions and how personal space can affect mental health.

Where is personal space represented in the brain?

Many animals have a certain “flight zone” around their bodies which acts as a protective—and protected—buffer area. Though they may detect a predator far away, the animal is not likely to move to escape until the threat is within the flight zone (2). While personal space in humans and other social animals doesn’t function exactly like a flight zone, we can feel threatened or uncomfortable when it is intruded upon, so moving away is in some sense a defensive movement. Because of this, many older experiments examined the brain’s representation of peripersonal space, the space around the body, as part of a defense mechanism.

For example, in monkeys electrical stimulation in parts of the parietal and frontal lobes causes defensive movements like ducking, squinting, and blocking—as if responding to something moving too close to the body by protecting the head and eyes. Recordings from neurons in these brain areas revealed that they respond to multiple sources of sensory information—such as visual, tactile, and auditory signals. Each neuron has a receptive field, the region in space where the cell responds to sensory stimuli. Researchers discovered that cells in these brain regions tile the peripersonal space with their receptive fields “like bubbles of space anchored to the body’s surface”, allowing the population to represent the space surrounding the entire body. The activity of these neurons can also change with the amount of attention paid to the incoming sensory information, which suggests that these cells could help dynamically shape the perception of personal space (2).

However, it can be difficult to tell in these experiments if the animals are perceiving personal space similarly to humans—i.e. as a major setting for social interactions—especially since they did not examine interactions of the monkey with other animals. To investigate the human brain’s representation and perception of personal space, researchers have used functional magnetic resonance imaging (fMRI) to examine areas of the brain that seem to be involved in representing different kinds of stimuli as they approach the body. These studies have implicated some of the same brain regions studied in monkeys, namely parts of the parietal and frontal lobes, in mapping and paying attention to the space around the body. The VIP and dorsal intraparietal sulcus in particular seemed to differentiate between approaching and withdrawing faces. In addition, the researchers measured each subject’s personal space by measuring how close they could comfortably be from an experimenter, and found a negative correlation between personal space size and the coupling between these two areas, meaning that people who were comfortable being closer to others tended to have stronger coupling (3). These results suggest that areas located in the frontal cortex and parietal lobe could be involved in regulating the size of your personal space, and filtering through lots of stimuli in order to direct attention to intrusions into your personal space by other people. Personal space may seem like a basic concept, but it takes some complex processing in multiple interconnected brain regions just to set up its most fundamental functions.

How does personal space affect social interactions?

At the same time, personal space isn’t just for navigating our bodies around objects and other individuals—it also plays a key part in how we interact with and understand each other. In experiments done in the 1960s, psychologists observed that the radius of personal space that a person is comfortable allowing others into decreases with increasingly close personal relationships, and increases in proportion to the perceived impersonality of the setting (i.e. the home vs a workspace vs a city street). Behaving according to personal space conventions is key to successful social interaction, and these unspoken rules can be as nuanced as those social behaviors themselves. To really understand the brain’s dynamic perception of personal space, we also need to investigate the realm of social interactions. For one, in addition to representing space around the body, the parietal lobe and premotor cortex also contain mirror neurons, which respond to our own actions and when we observe others completing the same actions. Brain recordings in monkeys and functional imaging in humans have found populations of neurons that seem to encode intrusions into both our own and others’ personal space (4,5).

It also makes sense that because it acts as the setting for most interpersonal interactions, our experience of personal space is often emotionally charged. This includes negative emotions (like when someone gets in your face during a heated argument) and positive emotions (like when a friend goes in for a hug). These emotional responses are crucial in navigating social interactions, and can protect us from people exhibiting threatening body language. One brain region that could be involved in the affective experience of personal space is the amygdala, which is heavily implicated in many kinds of social functions and processing fearful or aversive stimuli. Researchers began to associate the amygdala with personal space after noticing that a patient, SM, with complete damage to the amygdala on both sides of her brain had reduced personal space. They found that while she understood the concept of personal space and was aware that closeness could make other people uncomfortable, SM reported little to no discomfort to extreme personal space intrusions, even standing “nose-to-nose with direct eye contact” for extended periods of time. This suggests that SM specifically lacked the negative emotional response to inappropriate closeness. When control subjects in an fMRI detected personal space intrusions, they showed increased activity in the amygdala, which supports this hypothesis (6,7). As neuroscientists study personal space in more behaviorally relevant ways, they are starting to understand how multiple complex systems work together to add depth to our experience of personal space, building layers of social and emotional responses.

Personal space and psychiatric disease

The amygdala is also an important region in studying psychiatric disorders, in part because abnormal social behavior and emotional responses are key features of so many disorders. For example, deficits in social interaction and communication are symptoms of autism spectrum disorder (ASD). Children with ASD tend to prefer a larger interpersonal distance, but may also show abnormalities in they way they interact with personal space. For example, these children may intrude on others’ space more frequently than other children, or walk between others during a conversation. And where age-matched controls decreased interpersonal space as they became more familiar with the other person, ASD patients were inflexible in their personal space (8,9). These observations could point to deficits in social learning, which some researchers hypothesize could be rooted in abnormal amygdala activity since the amygdala is a key player in many types of learning. Research into the brain regions and circuits controlling each aspect of personal space could lead to additional insights into how patients with ASD process information.

Interestingly, personal space area is also increased in patients with schizophrenia, and tends to be larger in people who reported higher levels of anxiety (10,11). Based on these kinds of observations, researchers, health activists, and public planners have long hypothesized about the links between mental illness and decreased personal space caused by crowding (12). It makes sense that behavior should change according to population density, especially for social animals, since population density can affect things like disease transmission, competition for resources, and social hierarchies. However, the mechanisms by which the brain perceives long-term crowding, and how this could cause brain circuits to change over time and alter behavior are still open questions.

Personal space is fundamental to how we experience the world—it’s how we know where our bodies fit in our physical surroundings, it’s how we use body language to communicate, and it influences how we function in large groups. By studying how the brain processes personal space, we can better understand complex processes like social cognition, and even to use neuroscience to change our cities or communities to concretely improve mental health. And in the meantime, let’s put our personal space to good use:

References

1           Smith KE, Faig KE. The role of flexibility in personal space preferences. J Neurosci 2014:10135–6. https://doi.org/10.1523/JNEUROSCI.1997-14.2014.

2           Graziano MSA, Cooke DF. Parieto-frontal interactions, personal space, and defensive behavior. Neuropsychologia 2006;44:845–59. https://doi.org/10.1016/j.neuropsychologia.2005.09.009.

3           Holt DJ, Cassidy BS, Yue X, Rauch SL, Boeke EA, Nasr S, et al. Neural correlates of personal space intrusion. J Neurosci 2014;34:4123–34. https://doi.org/10.1523/JNEUROSCI.0686-13.2014.

4           Brozzoli C, Gentile G, Bergouignan L, Ehrsson HH. A shared representation of the space near oneself and others in the human premotor cortex. Curr Biol 2013;23:1764–8. https://doi.org/10.1016/j.cub.2013.07.004.

5           Ishida H, Nakajima K, Inase M, Murata A. Shared mapping of own and others’ bodies in visuotactile bimodal area of monkey parietal cortex. J Cogn Neurosci 2010;22:83–96. https://doi.org/10.1162/jocn.2009.21185.

6           Kennedy DP, Gläscher J, Tyszka JM, Adolphs R. Personal space regulation by the human amygdala. Nat Neurosci 2009;12:1226–7. https://doi.org/10.1038/nn.2381.

7           Todd RM, Anderson AK. Six degrees of separation: The amygdala regulates social behavior and perception. Nat Neurosci 2009:1217–8. https://doi.org/10.1038/nn1009-1217.

8           Kennedy DP, Adolphs R. Violations of Personal Space by Individuals with Autism Spectrum Disorder. PLoS One 2014;9:e103369. https://doi.org/10.1371/journal.pone.0103369.

9           Gessaroli E, Santelli E, di Pellegrino G, Frassinetti F. Personal Space Regulation in Childhood Autism Spectrum Disorders. PLoS One 2013;8:e74959. https://doi.org/10.1371/journal.pone.0074959.

10        Deuš V, Jokiá-Begić N. Personal space in schizophrenic patients. Psychiatr Danub 2006;18:150–8.

11        Sambo CF, Iannetti GD. Better safe than sorry? The safety margin surrounding the body is increased by anxiety. J Neurosci 2013;33:14225–30. https://doi.org/10.1523/JNEUROSCI.0706-13.2013.

12        Kamal P, Gupta ID. FEELING OF CROWDING AND PSYCHIATRIC DISORDERS. Indian J Psychiatry 1988;30:85.