Hippocampus makes maps of social space, too

NEW YORK — Cells in a brain structure known as the hippocampus are known to be cartographers, drawing mental maps of physical space. But new studies show that this seahorse-shaped hook of neural tissue can also keep track of social space, auditory space and even time, deftly mapping these various types of information into their proper places.

“The hippocampus is an organizer,” says neuroscientist Howard Eichenbaum of Boston University.

Neuroscientist Rita Tavares described details of one of these new maps April 2 at the annual meeting of the Cognitive Neuroscience Society. Brain scans had previously revealed that activity in the hippocampus was linked to movement through social space. In an experiment reported last year in Neuron, people went on a virtual quest to find a house and job by interacting with a cast of characters. Through these social interactions, the participants formed opinions about how much power each character held, and how kindly they felt toward him or her. These judgments put each character in a position on a “social space” map. Activity in the hippocampus was related to this social mapmaking, Tavares and colleagues found.

It turns out that this social map depends on the traits of the person who is drawing it, says Tavares, of Icahn School of Medicine at Mount Sinai in New York City. People with more social anxiety tended to give more power to characters they interacted with. What’s more, these people’s social space maps were smaller overall, suggesting that they explored social space less, Tavares says. Tying these behavioral traits to the hippocampus may lead to a greater understanding of social behavior — and how this social mapping may go awry in psychiatric conditions, Tavares said.

The work emphasizes that the hippocampus is not just a mapper of space, Tavares says. Instead, it is a mapper of relationships. “It’s relational learning,” she says. “It’s everything in perspective.”

Other research, discussed at a meeting in February, revealed a role for the hippocampus in building a very different sort of map — a map of sounds. Stationary rats were trained to “move” through a soundscape of different tones, pushing a joystick to change the sounds to reach the sweet spot — the target tone. As the rats navigated this auditory world, nerve cells in their hippocampus were active in a way that formed a map, Princeton University neuroscientist Dmitriy Aronov reported in Salt Lake City at the annual Computational and Systems Neuroscience meeting. 

Cells in the hippocampus can also map time, keeping count as seconds tick by, Eichenbaum has found (SN: 12/12/15, p. 12). All of these types of information are quite different, but Eichenbaum argues that they can all be thought of as memories — another mental arena in which the hippocampus plays an important role. Organizing these memories into a sensible structure may be the big-picture job description of the hippocampus, he says. “What’s being tapped in all of these studies is that we are looking at a framework, whether it’s a physical spatial framework, a social space framework, a pitch framework, or a time framework,” Eichenbaum says.