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Bruno Poucet

Publications and source records attributed to Bruno Poucet.

10 recordsLinked to original sources
PubMed2006

Cooperation between the hippocampus and the entorhinal cortex in spatial memory: a disconnection study.

It has been recently shown that lesions of parahippocampal areas including the entorhinal cortex do not disrupt place learning in the water maze, suggesting that the hippocampo-cortical circuitry is not important for spatial memory [Burwell RD, Saddoris MP, Bucci DJ, Wiig KA. Corticohippocampal contributions to spatial and contextual learning. J Neurosci 2004;24:3826-36]. The aim of the present study was to tax more directly the cooperation between the hippocampus and entorhinal cortex in two different spatial tasks, a place navigation task and a spontaneous object exploration task, using a disconnection procedure. Damaging the entorhinal-hippocampal system induced impairments in the two tasks but only in the spatial object exploration task rats with contralateral lesions displayed a greater deficit than rats with ipsilateral lesions. The results suggest that the cooperation between the hippocampus and the entorhinal cortex is modulated by the nature of the task and the cognitive processes involved in formation of spatial memory.

Animals↗
PubMed2005

Functional interaction between the associative parietal cortex and hippocampal place cell firing in the rat.

The hippocampus and associative parietal cortex (APC) both contribute to spatial memory but the nature of their functional interaction remains unknown. To address this issue, we investigated the effects of APC lesions on hippocampal place cell firing in freely moving rats. Place cells were recorded from APC-lesioned and control rats as they performed a pellet-chasing task in a circular arena containing three object cues. During successive recording sessions, cue manipulations including object rotation in the absence of the rat and object removal in the presence of the rat were made to examine the control exerted by the objects or by non-visual intramaze cues on place field location, respectively. Object rotations resulted in equivalent field rotation for all cells in control rats. In contrast, a fraction of place fields in APC-lesioned rats did not rotate but remained stable relative to the room. Object removal produced different effects in APC-lesioned and control rats. In control rats, most place fields remained stable relative to the previous object rotation session, indicating that they were anchored to olfactory and/or idiothetic cues. In APC-lesioned rats, a majority of place fields shifted back to their initial, standard location, thus suggesting that they relied on uncontrolled background cues to maintain place field stability. These results provide strong evidence that the hippocampus and the APC cooperate in the formation of spatial memory and suggest that the APC is involved in elaboration of a hippocampal map based on proximal landmarks.

Action Potentials↗
PubMed2004

Entorhinal cortex lesions impair the use of distal but not proximal landmarks during place navigation in the rat.

Rats with entorhinal cortex lesions were trained in two versions of the place navigation task in the Morris water maze. In the distal condition, they had to locate the hidden platform on the basis of remote landmarks, while in the proximal condition, they had to rely only on a configuration of proximal objects, placed directly in the pool. Entorhinal rats were impaired in using distal landmarks but were able to use proximal landmarks to navigate toward the platform. These results suggest that the use of distal and proximal landmarks during navigation involves activation of different neural structures. They also suggest, in agreement with previous data, that there are two distinct landmark-processing systems, one devoted to the processing of proximal landmarks and the other to the processing of distal landmarks.

Animals↗
PubMed2004

Representation of objects in space by two classes of hippocampal pyramidal cells.

Humans can recognize and navigate in a room when its contents have been rearranged. Rats also adapt rapidly to movements of objects in a familiar environment. We therefore set out to investigate the neural machinery that underlies this capacity by further investigating the place cell-based map of the surroundings found in the rat hippocampus. We recorded from single CA1 pyramidal cells as rats foraged for food in a cylindrical arena (the room) containing a tall barrier (the furniture). Our main finding is a new class of cells that signal proximity to the barrier. If the barrier is fixed in position, these cells appear to be ordinary place cells. When, however, the barrier is moved, their activity moves equally and thereby conveys information about the barrier's position relative to the arena. When the barrier is removed, such cells stop firing, further suggesting they represent the barrier. Finally, if the barrier is put into a different arena where place cell activity is changed beyond recognition ("remapping"), these cells continue to discharge at the barrier. We also saw, in addition to barrier cells and place cells, a small number of cells whose activity seemed to require the barrier to be in a specific place in the environment. We conclude that barrier cells represent the location of the barrier in an environment-specific, place cell framework. The combined place + barrier cell activity thus mimics the current arrangement of the environment in an unexpectedly realistic fashion.

Animals↗
PubMed2002

Relationships between place cell firing fields and navigational decisions by rats.

This study examined the performance of spatial problems by rats when purely behavioral manipulations disturb the relationship between the place cell representation and the cues used to solve the problems. Place cells were recorded while rats performed a task in which they had to locate a goal in a gray cylinder. In the "far" task, the unmarked goal was displaced by a large fixed distance from a white card on the cylinder wall. In the "near" task, the unmarked goal was directly in front of the card. Finally, in the "cue" task the goal was marked by a black disk on the cylinder floor. Relationships between visible stimuli and place cell activity were manipulated by conducting either "hidden" (with the rat in its home cage) or "visible" (with the rat in the recording apparatus) rotations of the wall card and, when present, independent rotations of the black disk. Hidden card rotations generally caused equal firing field rotations, whereas visible card rotations often did not cause fields to move. In the far task, visible card rotations were associated with a strong decrease of correct responses in the card-referred goal area. Most rats tended to search the goal in the field-referred area. In the near task, visible card rotations were associated with a moderate decrease of performance, with rats searching the goal at the wall card. Finally, field placements had no effect on performance in the cue task. Thus, visible rotations tended to disrupt the relationship between firing fields and cues in all tasks but impaired performance only in the task that required map-based navigation. These results provide strong new evidence in favor of the spatial mapping theory of hippocampal function.

Animals↗
PubMed2002

Remapping of place cell firing patterns after maze rotations.

When place cells are recorded from rats running on an elevated T-maze inside a curtained enclosure that contains distinct, experimenter selected stimuli, rotations of the maze plus stimuli cause equal rotations of firing fields. Here, we examined the effects of conflicting rotations of a T-maze relative to a laboratory frame that contained a large number of fixed stimuli in the environment and asked whether positional firing patterns stayed in register with the maze or the room cues or were modified in some more complex way. After maze rotations of 90 degrees, 180 degrees or 270 degrees, firing fields were stable in the laboratory frame and thus shifted to a different maze arm. In contrast, rotations of 45 degrees or -45 degrees resulted in dramatic changes of positional firing patterns regardless of their initial position on the maze. Crucially, even cells whose fields were initially on the central platform underwent major firing pattern alterations although the view of the environment from the platform was unchanged by such rotations. Finally, we found that altering the visual appearance by removing without rotation one or two maze arms did not alter firing fields on the remaining part of the maze. Thus, the "remappings" caused by 45 degrees rotations could result from the disturbed relationship between all arms and the room cues or from the changes in the possible paths the animal can take in the environment. Taken together, our results provide an example of combinatorial coding by the hippocampus, in which the place cell representation of the environment was seen to be modified as a unit and not piecewise according to locally available stimuli.

Animals↗
PubMed2002

Properties of place cell firing after damage to the visual cortex.

Hippocampal place cells were recorded while rats with lesions of the striate visual cortex foraged for food pellets in a cylindrical arena. Compared to control rats, rats with striate damage had place cells whose firing was less well organized in space, according to a measurement of spatial coherence. More importantly, the spatial location of firing fields in rats with striate lesions was poorly controlled by three-dimensional objects, unlike the fields of either normal sighted rats or early blind rats. These findings suggest a possible contribution of the striate visual cortex to the selection of cues used for anchoring place cell firing fields in space.

Action Potentials↗
PubMed1999

Homotopic septal grafts combined with a hydrogel bridge promote functional recovery in rats with fimbria-fornix lesions: A unit recording study.

Fimbria-fornix lesions abolish the hippocampal electrophysiological activity time-locked to the theta rhythm and alter some functional characteristics of place cells. The present experiment investigated whether homotopic grafts of fetal septal cells can alleviate some of these alter-ations when combined with a polymeric hydrogel bridging a fimbria-fornix lesion-cavity. Eleven months after grafting surgery, unit recordings were obtained from hippocampal neurons of seven rats [two sham-operated (S), two lesion-only (L) and three grafted (G)] while they explored a radial maze. The lesions induced dramatic loss of hippocampal acetylcholinesterase(AChE)-positive reaction products. Surviving grafts were found in the three grafted rats and several AChE-positive processes could be observed in the polymeric hydrogel, as well as in the most dorsal portion of the hippocampal parenchyma. Of 168 recorded units, 132 were hippocampal interneurons (i.e., fired rapidly everywhere in the maze), and 36 were pyramidal place cells (i.e., fired only when the rat was in a specific location in the maze, the place field). The overall firing characteristics of either cell type were similar in S, L and G rats. However, while none of the interneurons recorded from L rats was found to fire rhythmically, a significant proportion of interneurons recorded from S and G rats had an activity pattern time-locked to the theta rhythm [S: 16/19 (84 %); G : 22/70 (31 %)]. In addition, the increase in firing activity observed in interneurons recorded from S rats when they were moving was disrupted in cells from L rats, but partially restored in cells from G rats. Concerning place cells, most (93 %) place fields in S rats were stable relative to extra-maze cues when the radial maze was rotated, while they followed the maze rotation in both L and G rats. Because of the low number of rats used, the present results should be considered with caution. Nevertheless, they indicate graft-induced recovery of some properties of hippocampal function following fimbria-fornix damage, and suggest that homotopic transplants of projection neurons may foster some func-tional recovery when provided with a biomaterial allowing the host or grafted neurons to cross the lesion cavity.

Journal Article↗
PubMedDate not supplied

Place cells, neocortex and spatial navigation: a short review.

Hippocampal place cells are characterized by location-specific firing, that is each cell fires in a restricted region of the environment explored by the rat. In this review, we briefly examine the sensory information used by place cells to anchor their firing fields in space and show that, among the various sensory cues that can influence place cell activity, visual and motion-related cues are the most relevant. We then explore the contribution of several cortical areas to the generation of the place cell signal with an emphasis on the role of the visual cortex and parietal cortex. Finally, we address the functional significance of place cell activity and demonstrate the existence of a clear relationship between place cell positional activity and spatial navigation performance. We conclude that place cells, together with head direction cells, provide information useful for spatially guided movements, and thus provide a unique model of how spatial information is encoded in the brain.

Animals↗