The Neuroscience of Interpersonal Space

In psychiatry space is an important factor when approaching patients. Psychotic patients can easily misinterpret someone approaching as invading their privacy. Other patients admitted to a hospital value their privacy which is often very limited in crowded units. The space between people creates and defines the social dynamics of our interactions with others. You can probably remember situations in which the space between yourself and others was beyond the painful or even embarrassing limit. In social psychology, the space around the body has been defined as the ‘area individuals maintain around themselves into which others cannot intrude without arousing discomfort or even withdrawal’

This recent excellent article discussed here has the aim of developing a framework to investigate and interpret the neural mechanisms of ‘social space’. It is an extensive essay on the subject but I will focus on the neuroscience and neuropsychological part of this essay in this post because it fascinated me.

The terms used to describe body space are:

• The space outside of reach is referred to as extrapersonal (far) space
• The space within reaching distance is referred to as peripersonal (near) space
• The space directly on the body surface is commonly known as personal space

How is that space around the body defined in human beings? Which neural mechanisms underly the interpersonal space?
Evidence from neuropsychological studies:

Neglect of extrapersonal space is often seen after lesions of lateral intraparietal areas and frontal eye fields

Neglect for near space or peripersonal space is seen after lesions of ventral intraparietal areas and ventral premotor cortex

So extrapersonal and peripersonal space relies on two independent frontoparietal systems of the brain. This dissociation has also been found in trancranial magnetic stimulation research in healthy controls.

From animal research it is learned that for the peripersonal space information from the dorsal and ventral visual streams is necessary and when reaching in the extrapersonal space this system integrates with motor information in the inferior parietal lobe forming a visuo-motor representation of peripersonal space or ‘vision for action’ space.

Together, body space and external space form a ‘practical space’ for interacting with the world. Using our hands to reach towards and grasp objects has the effect of ‘shrinking’ or ‘de-distancing’ external space, such that ‘out-there’ is brought ‘here’ or far space is shrunk to the level of near space.

When we use objects the boundaries between here and there, between body space and external space become blurred. If we drive a car the car is often felt as being part of the body, a kind of extended body schema.

Neurophysiological and behavioral studies in humans and non-human primates have suggested the cells encoding peripersonal space around the hand to be dynamic, extending a virtual body envelope not only around the hand but also non-body objects within it, such as tools and artificial limbs.

This research shows that there are populations of cells that encode body space in certain bran areas. Their acitivty is further modulated by interactions with objects. Through experimental manipulation of such interactions it can be learned that the spatial extend of body space is between 30 to 70 centimeters.
This model doesn’t take in to account other important factors with influence on personal space such as higher processes in the brain: attention, emotion and motivation. This needs further research

Why is this important
Given the increasing density of our populations this research can provide a richer interpretation of findings from neuroimaging studies of prosocial behavior which may further insights into populations with social dysfunction. More specific, the increasing use of personal music systems on public transport and whilst walking in public may suggest a need for people to create their own personal ‘space’ that cannot be shared by others. Although the links between personal space and mental illness have not been studied intensively the investigation of the neural mechanisms of interpersonal spatial perception and behavior could provide new insights into the pathophysiology of disorders of social functioning such as social phobia, social anxiety, autism and schizophrenia.

Lloyd, D. (2009). The space between us: A neurophilosophical framework for the investigation of human interpersonal space Neuroscience & Biobehavioral Reviews, 33 (3), 297-304 DOI: 10.1016/j.neubiorev.2008.09.007