Who hasn’t wanted to snap their fingers and dive into the pages of the gorgeous places featured in National Geographic? Caught in a miserable physics exam that you haven’t studied for? No problem, with teleportation you can be whisked away to an expedition to Mars or an Australian beach. Afraid of heights but curious about skydiving? Immersion into an artificial, computer-simulated environment can emulate the look and feel of the real thing without any danger or risk. Virtual reality enables the military to train pilots to fly planes without leaving the safety of the base. Virtual environments are almost limitless in scope, allowing researchers to study complex motor behaviors. These virtual environments are often experienced with a head mounted display that allows the participant to move freely within the perceived environment — be it a pre-historic landscape or a lunar landing.
In exciting work published by the Ekstrom lab at UC Davis in Neuron, researchers used virtual reality to tackle the function of hippocampal neural oscillations in spatial navigation. While it is known that the hippocampus plays a role in navigation and memory, the specific computational processes controlling complex behavior remains unknown. It is thought though that theta oscillations are present whenever the hippocampus is active. Two competing hypotheses have emerged as to why the brain produces low frequency (delta/theta band) oscillations: 1) Is it in response to sensorimotor processing? 2) Are these oscillations playing a role in memory processing? To solve this debate experimentally, the team recorded hippocampal EEG activity of patients who were being monitored for seizure activity while they explored a virtual environment containing teleporters.
In this experiment, the patients experienced a virtual environment that allowed them to move through space without actually navigating with visual and motor cues. The patients played a computerized virtual-reality navigation game, in which they had to navigate to a particular destination. The patients used a joystick to control their movement (like a real video game) and were allowed to perform certain science-fiction type movements, like rapid teleportation. When the patients entered the “teleporter,” the screen went completely blank and after a delay, they entered a new environment. Because there was no visual information during teleportation, this task enabled the researchers to examine what happened to brain activity when spatial location was updated without sensory cues. This was the first study in which human patients were using a task that removed all sensory cues during navigation. The hippocampal low-frequency oscillations continued even in a task that did not require sensory processing to move through space.
Theta oscillations are active during movement in a virtual reality environment. Entering the teleporter did not decrease the power of the theta oscillations. The important finding to come out of this study is that the frequency of the oscillations occurring during the virtual reality “teleportation” experiment contained spatial information. The distance teleported was reflected by a change in the pattern of oscillation. This finding suggests that these mysterious low-frequency hippocampal oscillations play a role in memory-related spatial updates rather than sensory-related navigation. This work supports the theory that these low-frequency oscillations organize the firing of neurons during memory encoding and retrieval events. The neural computations of the hippocampus in controlling complex behaviors could have implications for how the brain makes decisions about directing future movement. Could it be that theta oscillations play a role in the neural representation of time?
Images by Jooyeun Lee.
Vass et al., 2016 L.K. Vass, M.S. Copara, M. Seyal, K. Shahlaie, S.T. Farias, P.Y Shen, A.D. Ekstrom Neuron 89 (2016) pp. 1180-1186