With phrases such as "the distant future" or "a long meeting", we regularly use distance-related words to describe time; and in metaphors describing "close friends" or "distant cousins", we use them to describe our social relationships. Researchers now think they know why - these figures of speech are rooted in a shared computation system in our brains.
The human brain, it seems, uses the same neural centers and methods to conceptualize "nearness" in space, time and social relations.
Using fMRI scans, Dartmouth neuroscientists Thalia Wheatley, Carolyn Parkinson and Shari Liu discovered common focal points of brain activity among volunteers as they looked at photos of friends vs. those of acquaintances, at objects seen from close up vs. far away, and as they read passages which referred to the immediate future vs. the distant future.
Their results indicate that, for computational efficiency, the human brain uses a common neural code to represent space, time and social "distance". Objects, times and people who are considered "close" use one pattern of activity, while those which are considered "distant" activate a second.
This echoes theories proposed by cognitive linguists, who say that we speak of abstract relationships using physical expressions such as our "inner circle" because we think of these relationships in such terms.
The experiment also seems to bolster Construal Level Theory (CLT), which posits that any form of distance means the same thing mentally, whether it's distance from the present moment, or from a person's own subjective experience. Dr. Wheatley says this explains why we tend to talk about time and relationships using metaphors for physical distance - such metaphors mirror the neural processes occuring in our brains, as we consider space, time or degrees of social connection.
Co-author Dr. Parkinson believes this convenient multipurposing of the same neural network is an example of "exaptation", where an existing biological, neural or genetic function is co-opted - used in a new or expanded way. Primates long ago evolved a brain system for representing space, so rather than evolving a completely new system, she says, the existing one has expanded to also represent time, and later to represent social relationships.
All three perception systems - spatial, temporal and social - share the feature of egocentricity: space is understood as distance radiating outward with ourselves at the center; we also perceive ourselves to be at the center of the present moment, and at the center of a social network populated by people at varying distances from us. Objects are located at various directions and distances from us in physical space; events are perceived at various distances in the future or past; and people are mentally placed at various points within a social web, the perceived distance from us depending upon the strength of our mutual connections. In fact, says the team, only minor adaptations are required to adapt nearly any egocentric reference system to the brain's spatial perception system.
According to their studies, the right inferior parietal lobule (IPL) acts as a flexible hub, using a "parsimonious encoding of proximity to self in spatial, temporal, and social frames of reference".They add that the IPL evolved to represent one's body in space and to guide sensorimotor transformations - using mental coordinates of a target to create coordinate-based instructions for muscle activation patterns. As the network expanded during the human brain's evolution, this coordinate-tracking capacity was recycled to work in increasingly abstract manners - calculating the temporal and social "distance" of objects rather than physical distances.
The main activity was clustered within the right IPL, but this region is part of a larger neural network called the frontoparietal control network (FPCN). In addition to the Right IPL, the circuit they discovered also engages the right temporal parietal junction (TPJ). Together, these two regions cooperate to help generate one's unique sense of self. The right IPL seems to represent space radiating out from the self, while the right TPJ supports mental distinctions between one's self vs. others.
The FPCN also comprises two brain circuits called the Default Mode Network (DMN), which processes internally-directed thought, and the Dorsal Attention Network (DAN), which processes externally-directed thought. The network activated by the experiment extended into additional regions (the superior temporal, supramarginal and angular gyri), as well as a small cluster in the medial occipital lobe, the brain's primary vision-processing center. The medial (central) region of the occipital lobe activates when picturing images during distance comparisons.
The supplementary motor area (SMA) and inferior frontal gyrus (IFG) are also thought to play a part; since both participate in retrieving spatial locations from memory, they may be also participate in accessing temporal and social frames of reference.
For a primer on brain anatomy and neuroscience, I recommend the free publication entitled Brain Facts - a Primer on the Brain and Nervous System from the Society for Neuroscience
Neuroscience Online, from the University of Texas Medical School
The Brain from Top to Bottom, an Interactive Website about the Brain and Human Behavior by McGill University
Or any of dozens of free Open Courseware programs offered by the greatest universities in the world:
Of course, you can also order PDF or paperback versions of my books ;-)
Sources: Dartmouth study provides first evidence of common brain code for space, time, distance
press release, February 4, 2014, John Cramer, Dartmouth College
A Common Cortical Metric for Spatial, Temporal, and Social Distance, C. Parkinson, S. Liu, T. Wheatley, Journal of Neuroscience, 2014; 34 (5): 1979 DOI: 10.1523/JNEUROSCI.2159-13.2014
"Metaphor, Exaptation and Harnessing", Janet Kwasniak, February 6, 2014, Neuro-patch blog
Old cortex, new contexts: re-purposing spatial perception for social cognition, C. Parkinson, S. Liu, T. Wheatley, Frontiers in human neuroscience, 2013; 7 PMID: 24115928
Note: This article is a copyright-protected excerpt from the 2014 revised edition of The Path Book I: Origins, to be published this September by Polyglot Studios, KK and available direct or on Amazon.com.