Background, but not foreground, spatial cues are taken as references for head direction responses by rat anterodorsal thalamus neurons

Two populations of limbic neurons are likely neurophysiological substrates for cognitive operations required for spatial orientation and navigation: h ippocampal pyramidal cells discharge selectively when the animal is in a ce rtain place (the "firing field") in the environment, whereas head direction cells discharge when the animal orients its head in a specific, "preferred " direction. Cressant et al. (1997) showed that the firing fields of hippoc ampal place cells reorient relative to a group of three-dimensional objects only if these are at the periphery, but not the center of an enclosed plat form. To test for corresponding responses in head direction cells, three ob jects were equally spaced along the periphery of a circular platform. Prefe rred directions were measured before and after the group of objects was rot ated. (The rat was disoriented in total darkness between sessions). This wa s repeated in the presence or absence of a cylinder enclosing the platform. When the enclosure was present, the preferred directions of all 30 cells r ecorded shifted by the same angle as the objects. In the absence of the enc losure, the preferred directions did not follow the objects, remaining fixe d relative to the room. These results provide a possible neurophysiological basis for observations from psychophysical experiments in humans that back ground, rather than foreground, cues are preferentially used for spatial or ientation.