The effects of changes in the environment on the spatial firing of hippocampal complex-spike cells

Abstract

Using the techniques set out in the preceding paper (Muller et al., 1987), we investigated the response of place cells to changes in the animal's environment. The standard apparatus used was a cylinder, 76 cm in diameter, with walls 51 cm high. The interior was uniformly gray except for a white cue card that ran the full height of the wall and occupied 100 degrees of arc. The floor of the apparatus presented no obstacles to the animal's motions. Each of these major features of the apparatus was varied while the others were held constant. One set of manipulations involved the cue card. Rotating the cue card produced equal rotations of the firing fields of single cells. Changing the width of the card did not affect the size, shape, or radial position of firing fields, although sometimes the field rotated to a modest extent. Removing the cue card altogether also left the size, shape, and radial positions of firing fields unchanged, but caused fields to rotate to unpredictable angular positions. The second set of manipulations dealt with the size and shape of the apparatus wall. When the standard (small) cylinder was scaled up in diameter and height by a factor of 2, the firing fields of 36% of the cells observed in both cylinders also scaled, in the sense that the field stayed at the same angular position and at the same relative radial position. Of the cells recorded in both cylinders, 52% showed very different firing patterns in one cylinder than in the other. The remaining 12% of the cells were virtually silent in both cylinders. Similar results were obtained when individual cells were recorded in both a small and a large rectangular enclosure. By contrast, when the apparatus floor plan was changed from circular to rectangular, the firing pattern of a cell in an apparatus of one shape could not be predicted from a knowledge of the firing pattern in the other shape. The final manipulations involved placing vertical barriers into the otherwise unobstructed floor of the small cylinder. When an opaque barrier was set up to bisect a previously recorded firing field, in almost all cases the firing field was nearly abolished. This was true even though the barrier occupied only a small fraction of the firing field area. A transparent barrier was effective as the opaque barrier in attenuating firing fields. The lead base used to anchor the vertical barriers did not affect place cell firing.(ABSTRACT TRUNCATED AT 400 WORDS)

Conjoint Control of Hippocampal Place Cell Firing by Two Visual Stimuli

“…The key difficulty is that the magnitude of the shape changes used by O'Keefe and Burgess 1996 were large enough that they induced in some cells major changes in firing pattern shape or suppression of firing fields. In agreement with earlier experiments on doubling the size of an apparatus (Muller and Kubie 1987), O'Keefe and Burgess 1996 found that the fields of some cells were strongly altered in one or more rectangular apparatuses, putting the data outside of our discourse. We predict, however, that repeating the O'Keefe and Burgess 1996 experiment with smaller (e.g., 20–30%, instead of 100%) changes of wall length would leave all fields recognizable and therefore provide a test of the viability of a modified vector-field approach.…”

“…Changes in the size or aspect ratio of a recording box can induce changes in the size and shape of firing fields (Muller and Kubie 1987; O'Keefe and Burgess 1996). In some cases, lengthening the box can cause a field with a single peak to develop two peaks or even to come apart into two pieces as though the field had two components, one associated with a wall and the other with the opposite wall (O'Keefe and Burgess 1996).…”

“…During rotations of a single card (Muller and Kubie 1987) or equal rotations of both cards, fields act as though they are rigidly connected to a pivot at the apparatus center and that the pivot is turned through the same angle by which the stimuli are rotated. For instance, the rotational field movement that would be induced by the black card is V ′ B .…”

Conjoint Control of Hippocampal Place Cell Firing by Two Visual Stimuli

“…The behavioral, surgical, electrical recording, and rat-tracking methods used in this paper are similar to those used in earlier work from this laboratory (Muller and Kubie 1987; Muller et al 1994) and are only briefly summarized. The focus is therefore on methods specific to this work.…”

“…We then asked how firing fields were affected if the angular distance between the two cards was made either smaller or greater by 25°. These “reconfigurations” did not cause fields to disappear nor to move over large distances as occurs in remapping (Muller and Kubie 1987; Thompson and Best 1989; Bostock et al 1991; Kentros et al 1998), allowing us to look for patterns of field movements across the cell sample.…”