Interactions between location and task affect the spatial and directional firing of hippocampal neurons

Abstract

When rats forage for randomly dispersed food in a high walled cylinder the firing of their hippocampal "place" cells exhibits little dependence on the direction faced by the rat. On radial arm mazes and similar tasks, place cells are strongly directionally selective within their fields. These tasks differ in several respects, including the visual environment, configuration of the traversable space, motor behavior (e.g., linear and angular velocities), and behavioral context (e.g., presence of specific, consistent goal locations within the environment). The contributions of these factors to spatial and directional tuning of hippocampal neurons was systematically examined in rats performing several tasks in either an enriched or a sparse visual environment, and on different apparati. Place fields were more spatially and directionally selective on a radial maze than on an open, circular platform, regardless of the visual environment. On the platform, fields were more directional when the rat searched for food at fixed locations, in a stereotypic and directed manner, than when the food was scattered randomly. Thus, it seems that place fields are more directional when the animal is planning or following a route between points of special significance. This might be related to the spatial focus of the rat's attention (e.g., a particular reference point). Changing the behavioral task was also accompanied by a change in firing location in about one-third of the cells. Thus, hippocampal neuronal activity appears to encode a complex interaction between locations, their significance and the behaviors the rat is called upon to execute.

Conjoint Control of Hippocampal Place Cell Firing by Two Visual Stimuli

“…When the animal is put back in the environment, an unspecified recognition process decides whether the current surroundings are familiar or novel. We imagine that the decision rules are very complex and depend on the behavioral requirements in the environment as well as the immediate sensory information (Markus et al 1995; Zinyuk et al 2000). We do not consider further what happens if a new template must be built.…”

The hippocampal debate: are we asking the right questions?

“…By this point, it is pretty much accepted that under certain conditions, hippocampal pyramidal cells show correlations to non-spatial aspects [48,69,71,101,109,157,238,239,246,247,250] (see [33,173] for reviews, but see [147] for an alternative viewpoint). These non-spatial aspects include when animals change task within an environment [101], in response to components of a task in which goals change [48,69,157,247], even after salient events [202].…”

“…These non-spatial aspects include when animals change task within an environment [101], in response to components of a task in which goals change [48,69,157,247], even after salient events [202]. In addition, hippocampal cells show place field changes with changes in environments or the available constellation of cues [17,90,93,129,148,181,219,223,250].…”

“…Interestingly, spatial cues are sometimes represented discretely: on a linear track, cells differentiate the two directions of travel [67,101,109,174]. However, when allowed to experience all directions without limitations (such as when foraging within an open environment), cells do not show any directional dependence at all [101,128,130].…”

“…However, when allowed to experience all directions without limitations (such as when foraging within an open environment), cells do not show any directional dependence at all [101,128,130]. We recently explored the moment of transition when animals turn around on linear tracks [174].…”