The human brain has a mechanism to encode individual location and people around us

Scientists know a lot about how rats navigate their social environment, but not much about the process of human spatial navigation.

Now, experimental research by a team of University of California Los Angeles scientists provides evidence that an encoding mechanism in the human brain governs how we know our physical location and the location of those around us.

The research appeared in the journal Nature, Dec. 23, 2020.

UCLA researchers tracked the brain rhythms of five individuals in a series of experiments in a room, walking toward a target on the wall and looking for a hidden target. The researchers also tracked the brain rhythms when one participant sat in the room and observed another person performing the navigational tasks.

All participants were epilepsy sufferers who had a responsive neuro-stimulation device implanted to prevent epileptic seizures. During the experiment, they wore a backpack with brain recording equipment that connected wirelessly to the implanted electrodes in their brain. The backpack measured the intracranial electroencephalographic activity from the medial temporal lobe (MTL). 

The research team found that the low-frequency oscillations measured in the MTL increased as the participants neared the physical boundary (wall) from the inner part of the room. This was also true when they were observing a participant. When the participant got close to the wall, the person observing also had a low-frequency oscillatory pattern. This suggests a common coding mechanism in the brain to represent the location of one's self as well as someone else.

The oscillations were most prominent in the theta frequency band, the authors wrote, "with the strongest 'boundary' versus 'inner' power differences seen around 5-8 GZ for the observation task and a slightly wider frequency band (around 3-13 HZ) during self-navigation."

The researchers analyzed data for each participant separately and found consistent results. They also found that the oscillations occurred not continuously, but in bouts, approximately 10% to 20% of the time.

Of particular interest, researchers found that the theta power registered higher when the participants searched for a target, than when they walked toward a sign on the wall. The researchers surmise that this may be because simply walking toward a sign is cognitively less demanding than searching for a target.

The researchers ruled out the effect of other variables on oscillation changes. Eye movements, moving speed, or direction toward or away from the boundary did not affect the results.

In addition to the increases in oscillation power in the theta frequency, the researchers found similar increases in the gamma frequency band, although the effects were "smaller and more variable" under the experimental conditions.

Significantly, the researchers found "strikingly similar" oscillation effects when the participants self-navigated or watched another participant self-navigate toward a boundary.

They conclude: "These findings provide, to our knowledge, the first evidence for a mechanism in the human brain that encodes another person's spatial location--essential, for example, in social situations in a shared environment where keeping track of another's location is necessary."

"Moreover," the researchers said, "boundary-anchored neural representations of location for both self and other are modulated by cognitive state, and strengthened when the encoding of location is of higher behavioral relevance."

Many questions remain for follow-up. The authors note that future research should look at the brain mechanism in more complex scenarios.