Biomedical subjects

B Poucet

Publications and source records attributed to B Poucet.

At least 19 recordsLinked to original sources

PubMed2000

Contribution of multiple sensory information to place field stability in hippocampal place cells.

Hippocampal place cells in rats display spatially selective firing in relation to both external and internal cues. In the present study, we assessed the effects of removing visual and/or olfactory cues on place field stability. Place cell activity was recorded as rats searched for randomly scattered food in a cylinder. During an initial recording session, the lights were on and the only available cue was a single white cue card. Following this session, three sessions were run in a row with the cue card removed. In addition, the lights were either turned off or left on and the floor was either cleaned or left unchanged, thus creating four conditions: dark/cleaning, dark/no cleaning, light/cleaning, and light/no cleaning. A fifth session was run with the cue card back on the cylinder wall and the lights turned on. The rat remained in the cylinder during all sessions without being removed at any time. In the dark/cleaning and light/cleaning conditions, most place fields were not stable (i.e., abruptly shifted position). In addition, half of the cells stopped firing in the dark/cleaning condition. In contrast, in the dark/no cleaning and light/no cleaning conditions, most place fields remained stable across sessions. These results suggest that 1) rats are not able to rely on only movement-related information to maintain a stable place representation, 2) visual input is necessary for the firing of a large number of cells, and 3) olfactory information can be used to compensate for the lack of visuospatial information.

Action Potentials↗

PubMed2000

Hippocampal-parietal cortical interactions in spatial cognition.

Growing evidence suggests that the associative parietal cortex (APC) of the rat is involved in the processing of spatial information. This observation raises the issue of the respective functions of the APC and the hippocampus in spatial processing as well as of their possible interactions. In this paper, we review neuroanatomical, electrophysiological, and behavioral data that support the existence of such functional interactions. Our hypothesis is that the APC is involved in the initial combination of visuospatial information and self-motion information necessary for the integration of egocentrically acquired information into allocentrically coded information, the latter step being completed in the hippocampus. The dialogue between the hippocampus and the APC is therefore crucial, particularly when the elaboration and/or updating of an allocentric representation depends on complex combinations of visuospatial and self-motion information.

Animals↗

PubMed2000

Involvement of the hippocampus and associative parietal cortex in the use of proximal and distal landmarks for navigation.

Rats with dorsal hippocampus or associative parietal cortex (APC) lesions and sham-operated controls were trained on variants of the Morris water maze navigation task. In the 'proximal landmark condition', the rats had to localize the hidden platform solely on the basis of three salient object landmarks placed directly in the swimming pool. In the 'distal landmark condition', rats could rely only on distal landmarks (room cues) to locate the platform. In the 'beacon condition', the platform location was signaled by a salient cue directly attached to it. Rats with hippocampal lesions were impaired in the distal and to a less extent in the proximal landmark condition whereas rats with parietal lesions were impaired only in the proximal landmark condition. None of the lesioned groups was impaired in the beacon condition. These results suggest that the processing of information related to proximal, distal landmarks or associated beacon are mediated by different neural systems. The hippocampus would contribute to both proximal and distal landmark processing whereas the APC would be involved in the processing of proximal landmarks only. Navigation relying on a cued-platform would not require participation of the hippocampus nor the APC. Assuming that the processing of proximal landmarks heavily depends on the integration of visuospatial and idiothetic information, these results are consistent with the hypothesis that the APC plays a role in the combination of multiple sensory information and contributes to the formation of an allocentric spatial representation.

Animals↗

PubMed2000

Sensory and memory properties of hippocampal place cells.

The rat hippocampus contains place cells whose firing is location-specific. These cells fire only when the rat enters a restricted region of the environment called the firing field. In this review, we examine the sensory information that is fundamental to the place cell system for producing spatial firing. While visual information takes precedence in the control of firing fields when it is available, local (olfactory and/or tactile) cues combined with motion-related cues can permit stable spatial firing. Motion-related cues are integrated by hippocampal place cells, but in the absence of external cues do not support stable firing over long periods. While firing fields are based on a variety of sensory cues, they do not strictly depend on such cues. Rather, sensory information is important for activating the representation appropriate to the current environment as reflected by the firing properties of place cell ensembles. Specific sensory channels as well as the memory properties of place cells can support ongoing firing under manipulations of the environment. These memory features raise the question of the role of the place cell system in the acquisition, storage and retrieval of spatial information. Based on the existing literature about the effects of hippocampal lesions and about the metabolic activations in spatial memory tasks, we suggest that a function of the place cell system is to automatically provide the organism with information about its current location so as to allow for the rapid acquisition of novel information.

Animals↗

PubMed1999

Is the hippocampus of the rat part of a specialized navigational system?

The spatial mapping theory of hippocampal function proposes that the rat hippocampus is specialized for navigational computations, computations that allow the animal to solve difficult spatial problems. In this paper, we review evidence obtained by recording place cells and other "spatially tuned" cells from freely moving rats. Our main conclusion is that the nature of the signals carried by these cells and the ways in which the signals transform after changing the environment imply that the hippocampus and associated structures are able to represent aspects of the geometry of the environment.

Animals↗

PubMed1999

Further study of the control of place cell firing by intra-apparatus objects.

The angular positions of hippocampal place cell firing fields are accurately controlled by the position of a single salient cue card attached to the wall of a recording cylinder; when the card is rotated, fields rotate equally. In contrast, the control exerted by 3-dimensional objects placed directly in the recording arena depends on their arrangement. When three objects lie on the vertices of an isosceles triangle near the center of the cylinder they rarely exert any control over the angular positions of firing fields. However, if the isosceles triangle is dilated so that its vertices are against the apparatus wall, the objects exert virtually ideal control over angular field position. Why do the objects gain control when they are against the cylinder wall? One possibility is that the asymmetry in the object set is more easily detected when the objects are far apart so that they provide a better polarizing cue. This hypothesis assumes that the identity of individual landmarks is not recognized by the place cell system whereas their geometric arrangement provides crucial information for controlling place field positions. If this is true, putting the 3 objects against the cylinder wall on the vertices of an equilateral triangle should cause a loss of stimulus control over the angular positions of firing fields. To the contrary, we found that the firing fields of most place cells (23/29) were accurately controlled by the equilateral object arrangement. Moreover, 5/6 of the uncontrolled cells were in a single animal. These results bolster our previous suggestion that the centrally placed objects fail to control place field positions because the computations necessary to form a stable reference frame are very difficult when the animal can go between stimuli.

Action Potentials↗

PubMed1998

Spatial firing of hippocampal place cells in blind rats.

The rat hippocampus contains cells that are characterized by location-specific firing. Previous work has shown that the angular position of hippocampal place cell firing fields is accurately controlled by the position of visual cues, suggesting that vision plays a important role in triggering place cell activity. However, a role for other types of information has also been suggested because place cell activity can be recorded while animals are moving in the darkness. In this study, we asked whether place fields can get established in rats that have never seen their environment. We studied place cell activity in early blind rats and found that these rats had place cells very similar to those recorded from sighted rats. This result suggests that early vision is not necessary for normal firing of hippocampal place cells. Dynamic, motion-related information in conjunction with stimulus recognition seems to be sufficient.

Animals↗

PubMed1998

Evidence for the involvement of the rat prefrontal cortex in sustained attention.

Previous studies suggest that, in both humans and rats, the prefrontal cortex (PFC) is involved in both selective and divided attention. We have also shown that the PFC is involved in response selection and that its involvement is modulated by the cognitive effort required by the task. However, the role of the PFC is much less clear when no response selection is required. The purpose of the present experiments was to assess the role of the PFC in attentional functions with a low response-selection demand. We used two tasks in which information processing was effortful but where the demand on a response selection process is low. Moreover, we assessed two different types of visual attentional functions: selective attention (Experiment 1) and sustained attention (Experiment 2). The results showed a differential involvement for the PFC in the two tasks. Selective attention was not impaired by prefrontal lesions when the number of possible positions for the stimulus on which the subjects must focus was restricted to two (Experiment 1). In contrast, prefrontal rats were unable to sustain their attention long enough to detect, and react to, subtle variations in brightness (Experiment 2). This results suggests a dissociation between different types of attentional functions depending upon the integrity of the PFC. More specifically, results in Experiment 2 suggest an involvement of the PFC in sustained attention. Finally, the overall results show that even in tasks involving low demands on response selection the PFC is involved in attentional functions.

Animals↗

PubMed1997

Failure of centrally placed objects to control the firing fields of hippocampal place cells.

Previous work has shown that the angular position of hippocampal place cell firing fields is accurately controlled by the position of a single white cue card attached to the wall of a recording cylinder: when the card is rotated, fields rotate equally. In this study, we asked whether similar control could be exerted by three-dimensional objects placed directly in the recording arena. In each of several conditions, the locations of the objects relative to each other and their distances from the cylinder wall were fixed. In Experiment 1, the objects were all near the center of the cylinder. In this condition, the angular position of firing fields could, in general, not be predicted from the angular position of the object set. When a white wall card was added to the object arrangement, the stimulus ensemble exerted nearly ideal control over angular firing position. Nevertheless, when the card was withdrawn, the objects still did not control field position. In Experiment 2, place cells were recorded in the presence of two new arrangements of the same objects used in Experiment 1. In the "clustered objects" condition, the objects were placed next to each other, 10 cm from the wall. In the "objects-at-periphery" condition, the objects were put against the cylinder wall by equally increasing the distances among the objects. In both conditions, we found virtually ideal control by the objects over angular field position. These results indicate that the failure of stimulus control in Experiment 1 must be attributable to the arrangement of the objects and not to the nature of the objects themselves. Overall, the results are in line with behavioral studies that show that it is very difficult to teach rats to locate food relative to landmarks inside the behavioral arena.

Animals↗

PubMed1997

Searching for spatial unit firing in the prelimbic area of the rat medial prefrontal cortex.

The prelimbic area of the rat medial prefrontal cortex is anatomically connected to the CA1 layer of the temporal hippocampus. As cells recorded from this region of the hippocampus act as place cells (i.e., their firing is related to the animal's location in the environment), the possibility arises that the prefrontal recipients of hippocampal efferences also display spatial firing patterns. To examine this hypothesis, recordings were made from prelimbic frontal units while the position and head direction of the freely moving rat were simultaneously recorded by tracking two lights mounted on the rat's head. Of 42 cells recorded in this situation, none was found to have a firing pattern bearing a significant relationship to the animal's position or to its head direction. Rather, cell activity was modulated during specific behaviors such as food-searching or exploratory behaviors.

Animals↗

PubMed1997

The neuropsychology of spatial cognition in the rat.

This article provides a review of the neural mechanisms of spatial cognition in the rat. A survey of the literature shows that the rat has spatial capabilities that can be explained only if one assumes that it possesses a representation of some features of the environment. The scope of such a representation may, however, be more limited than what is implied by the hypothesis of a bird's-eye view of the environment. The best documented spatial ability of the rat is illustrated by its efficiency in performing the water maze navigation task. A review of recent neurobiological data collected while a rat was performing this task suggests that several brain structures make unique contributions to spatial navigation. In particular, the hippocampal formation and the associative (posterior) parietal cortex seem to handle different aspects of navigation and to be differentially involved in the various stages of spatial memory formation. Electrophysiological data support the hypothesis that the hippocampal formation is concerned with rapidly building associative memories of spatial relationships within the environment. In contrast, the associative parietal cortex might be involved in more abstract spatial processing, resulting in a metric representation of spatial information collected during movements.

Animals↗

PubMed1996

Effortful information processing in a spontaneous spatial situation by rats with medial prefrontal lesions.

Previous research has suggested that the rat prefrontal cortex might play a role in spatial information processing and in divided attention. More recent work showed that the effect of prefrontal lesions is more important when the task involves response selection in complex situations. The first aim of the present study was to test the effect of lesions of the prelimbic area of the rat prefrontal cortex in spatial exploration, a situation involving the processing of spatial and non-spatial information, but requiring no response selection. The second aim was to manipulate the degree of cognitive effort required by the task. The latter effect was tested by manipulating the number of items to explore. Rats explored either a simple (3 objects) or a complex (6 objects) situation. We reasoned that acquiring spatial information so as to react adequately to spatial or non spatial changes involved more effortful processing in the complex situation than in the simpler one. The results suggest that the medial prefrontal cortex is not crucially involved in effortful processing when the task requires no response selection.

Animals↗

PubMed1996

Effects of parietal cortex lesions on spatial problem solving in the rat.

The Maier 3-table task was used to examine spatial representations in rats with lesions of the parietal cortex. Some animals had anteriorly placed lesions, some posteriorly placed in cortical areas, sometimes regarded as 'parietal' in earlier studies. After 5 days of familiarization, animals were given 18 days of testing on the standard Maier task. Both parietal groups were initially impaired, but reached the same level of performance as controls by the end of the test period. Learning occurred both within and between sessions for the anterior group, but only between sessions for the posterior group. There was no major functional differentiation apparent on this task between the two 'parietal' areas. Rate of exploration increased in both parietal groups across test sessions as task performance improved. It is argued that the change in exploratory activity across sessions in parietal groups may reflect the adoption of a compensatory strategy which improved performance, but that improvement could also have been due to neural changes, as structures, such as the frontal cortex or hippocampus, assume some functions normally mediated by the parietal area.

Animals↗

PubMed1995

Nicotinic and muscarinic receptors in the rat prefrontal cortex: differential roles in working memory, response selection and effortful processing.

The aim of the present study was to evaluate the effects of cholinergic receptor blockade in the rat prefrontal cortex on cognitive processes. The nicotinic antagonists neuronal bungarotoxin and dihydro-beta-erythroidine and the muscarinic antagonist scopolamine were injected into the prelimbic area of the prefrontal cortex. Their behavioural effects were assessed in a T-maze to test reference memory (visual discrimination task) and working memory in delayed matching (MTS) and non-matching to sample (NMTS) tasks. Neuronal bungarotoxin produced a significant decrease in working memory performance in the MTS task but not in the NMTS task. In contrast, scopolamine impaired working memory in both MTS and NMTS tasks. Reference memory was not altered by any of the cholinergic antagonists. These results demonstrate a differential role of nicotinic and muscarinic receptors in the rat prefrontal cortex. Nicotinic transmission appears to be important in delayed response tasks requiring effortful processing for response selection, while the muscarinic system is involved in general working memory processes.

Acetylcholine↗

PubMed1995

Medial prefrontal lesions in the rat and spatial navigation: evidence for impaired planning.

Rats with medial prefrontal cortical lesions were tested in a modified water maze navigation task. In Stage 1, the rats were trained to locate a hidden platform from a single start location. They were then subjected to a series of trials during which a second start position was used (Stage 2). In Stage 3, the rats had to navigate to a new goal location from the 2 experienced start positions. Stage 4 required the rats to navigate to the same goal as in Stage 3, starting from 4 distinct positions. Finally, a single probe trial with no platform was conducted. Rats with prefrontal lesions were impaired only during Stage 4. This deficit was specific to the 2 start positions newly introduced during this stage, suggesting a dysfunction of planning processes. This impairment might result from a working memory deficit, precluding the animal from forming an adequate representation of the whole course of movements required to reach the platform.

Animals↗

PubMed1994

Place cells in the ventral hippocampus of rats.

Many cells recorded from the dorsal hippocampus of freely moving rats are intensely active only when the rat's head is in a particular part of its environment. For this reason, such units are called 'place cells'. We have investigated whether place cells are also found in the ventral hippocampus. Recordings were made from ventral hippocampal units while rats chased food pellets in a cylindrical arena. The rat's position was simultaneously recorded by tracking a light on the rat's head. Our data show the existence of cells in the ventral hippocampus whose positional firing patterns and electrophysiological properties are very similar to those of dorsal hippocampal place cells.

Action Potentials↗

PubMed1994

Effects of medial septal or unilateral hippocampal inactivations on reference and working spatial memory in rats.

The memory performances of rats receiving a reversible inactivation of either the medial septum or one side of the ventral hippocampus were compared in a radial arm maze task allowing the assessment of both working and reference memory. After pre-surgery training, rats were chronically equipped with bilateral cannulae into the ventral hippocampus and a single cannula into the medial septum. Following post-surgery retraining, animals received a series of test trials during which they received saline or lidocaine injections in either the medial septum or one side of the ventral hippocampus. Lidocaine injections in either structure resulted in both reference and working memory deficits. However, animals were more impaired after septal injections than after unilateral hippocampal injections. This result suggests that the septo-hippocampal formation acts as a functionally homogeneous structure essential for spatial processing.

Animals↗

PubMed1994

Working memory, response selection, and effortful processing in rats with medial prefrontal lesions.

This study examined the effects of lesions of the prelimbic area of the rat prefrontal cortex on acquisition and retention of nonmatching (NMTS) and matching-to-sample (MTS) tasks. Both tasks involved a reference and a working memory component, but only working memory was impaired by the lesions. A comparison of the 2 tasks revealed quantitatively similar deficits in postoperatively trained rats. In preoperatively trained rats, however, the deficits were more important in the MTS task than in the NMTS task. In addition, an effect of interference between successive trials was observed in the NMTS task but not in the MTS task. Perseverative tendencies were observed in the MTS task only. These results suggest that prefrontal lesions induce working memory deficits as a result of poor temporal encoding and increased susceptibility to interference and impair effortful processing, such as that engaged in response selection mechanisms.

Animals↗