Place cells in the real world (left): The picture on the left shows the top-down view of a room in which a rat runs. There are four colorful walls and a check pattern on the floor. In the middle of the room, there is a narrow track (white line) on which the rat runs. Spikes fired by a neuron are shown by blue tick marks above and below the white track. Spikes fired when the rat runs from left-to-right are shown below the track and those spikes fired when the rat runs from right-to-left are shown above the track. These data were recorded in the real world. Notice that the spikes (blue tick marks) occur at the same absolute position hence these are called place cells.
Place cells in virtual reality (right): These data were recorded in the virtual world. Note that the virtual world looks similar to the real world (other image). When the rat runs in this virtual world, the neurons fire at the same relative distance on the track in both movement directions, not at the same position as it does in the real world. We hypothesize that the neurons are actually computing relative distances using cues on the walls and self-movement in the virtual world. In the real word, the presence of nonspecific sensory stimuli on the track, such as smells and textures, are hypothesized to make the neurons active at the same position.
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