Abstract
Familiar landmarks have both an identity (e.g., White House) and a location in space (e.g., 1600 Pennsylvania Ave.). How are these two kinds of information represented in the brain? We addressed this issue by scanning University of Pennsylvania students with fMRI while they viewed images of 10 landmarks from the Penn campus. Images (22 views of each landmark; 220 total) were presented at 0.33 Hz in a continuous carry-over design (Aguirre, 2007). We observed two different kinds of adaptation effects relating to repetition of (i) landmark identity and (ii) spatial location. First, scene-responsive parahippocampal place area (PPA) and retrosplenial complex (RSC), as well as medial retrosplenial cortex, showed reduced response when two different images of the same landmark were shown on successive trials, suggesting that these regions represent individual places with some generalization across views. Second, the left anterior hippocampus exhibited adaptation corresponding to real-world distances between landmarks; specifically, response was more strongly reduced when the landmarks shown on successive trials were closer together on campus. Importantly, there was a dissociation between these two effects: PPA, RSC, and medial retrosplenial cortex did not show distance-related adaptation and left anterior hippocampus did not show adaptation for landmark identity. The landmark adaptation effect in PPA, RSC, and medial retrosplenial cortex is consistent with previous work implicating these areas in the coding of real-world places. The unexpected distance-related response in the left anterior hippocampus may reflect the retrieval of episodic memories about these locations in a way that is shaped by their positions in a larger spatial map.
This research was funded by NIH grant EY-016464 to R.A.E.