Bilateral postsubiculum lesions impair visual and nonvisual homing performance in rats

Abstract

Nearly all species rely on visual and nonvisual cues to guide navigation, and which ones they use depend on the environment and task demands. The postsubiculum (PoS) is a crucial brain region for the use of visual cues, but its role in the use of self-movement cues is less clear. We therefore evaluated rats' navigational performance on a food-carrying task in light and in darkness in rats that had bilateral neurotoxic lesions of the PoS. Animals were trained postoperatively to exit a refuge and search for a food pellet, and carry it back to the refuge for consumption. In both light and darkness, control and PoS-lesioned rats made circuitous outward journeys as they searched for food. However, only control rats were able to accurately use visual or self-movement cues to make relatively direct returns to the home refuge. These results suggest the PoS's role in navigation is not limited to the use of visual cues, but also includes the use of self-movement cues. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Figure 1.

Testing apparatus and analysis of homing performance. A, A single doorway was opened to allow entry to the refuge (shown at bottom), and all other doorways were blocked. A black curtain disguised all doorways to prevent visual detection of the refuge. B, Schematic of homing journey for a representative rat. The outward journey (thin blue line) was characterized by variable speed and frequent stops. Upon locating the single food pellet, the animal reoriented and made a relatively direct movement toward the perceived location of the refuge (thick red line). The angular deviation between the animal’s heading and the correct direction toward the refuge (dashed line) were calculated for the initial heading (return point) and the final heading (first point of contact with the wall).

Figure 2.

Histological reconstruction of PoS lesion. A, B, Coronal sections showing the left and right PoS from a control rat (A) and a PoS lesioned rat (B). NMDA injection produced extensive damage to the PoS. Arrowheads depict boundaries of the PoS. Scale bar, 1.0 mm. Approximate location of images is depicted in the inset diagram, 6.4 mm caudal to bregma. C, Diagram of the lesion area after NMDA injection into the PoS. Light gray represents the most extensive damage, and dark gray represents the least extensive damage. Diagram sections are labeled with approximate rostrocaudal distance from bregma (recreated from Kjonigsen et al., 2011).

Figure 3.

Homing performance in light. A, B, Outward (O, blue) and homeward (H, red) paths taken by representative control and PoS-lesioned rats. C, Both control and PoS lesioned rats showed greater mean speeds during the homeward segment than during the outward segment. D, Both groups of rats made relatively circuitous outward movements, but homeward movements were more direct only for the control rats. E, Homeward segments were more direct for control rats overall, and neither group showed changes across days of testing. F, Control rats, but not PoS lesioned rats, showed increased directness of homeward movements across the four trials within days. Mean ± SEM.

Figure 4.

Heading error and choice errors during the homeward segment in light. A, Initial heading error was significantly greater for PoS lesioned rats than for control rats. The heading error was significantly reduced between the initial and final headings for both groups, but error reduction did not differ between groups. B, PoS lesioned rats attempted to enter significantly more incorrect doorways than control rats. Mean ± SEM.

Figure 5.

Homing performance in darkness. A, B, Outward (O, blue) and homeward (H, red) paths taken by representative control and PoS-lesioned rats. C, Both control and PoS lesioned rats showed greater mean speeds during the homeward segment than during the outward segment. D, Both groups of rats made relatively circuitous outward movements, and homeward movements were somewhat more direct for the control rats. E, Homeward segments were more direct for control rats overall, and neither group showed significant changes across days of testing. F, Neither control nor PoS lesioned rats showed significant changes in the directness of their homeward movements across the four trials within days. Mean ± SEM.

Figure 6.

Heading error and choice errors during the homeward segment in darkness. A, Initial heading error was significantly greater for PoS lesioned rats than for control rats. The heading error was significantly reduced between the initial and final headings for both groups, but error reduction did not differ between groups. B, PoS lesioned rats attempted to enter significantly more incorrect doorways than control rats. Mean ± SEM.