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S I Wiener

Publications and source records attributed to S I Wiener.

At least 19 recordsLinked to original sources
PubMed2005

Spatially selective reward site responses in tonically active neurons of the nucleus accumbens in behaving rats.

To study how hippocampal output signals conveying spatial and other contextual information might be integrated in the nucleus accumbens, tonically active accumbens neurons were recorded in three unrestrained rats as they performed spatial orientation tasks on an elevated round rotatable platform with four identical reward boxes symmetrically placed around the edge. The partially water-deprived rats were required to shuttle either between the pair of reward boxes indicated by beacon cues (lights in the boxes) or between the pair of boxes occupying particular locations in relation to environmental landmark cues. In 43/82 neurons, behaviorally correlated phasic modulations in discharge activity occurred, primarily prior to or after water was provided at the reward boxes. Twenty-two had inhibitory modulation, 12 excitatory, and nine were mixed excitatory and inhibitory. Although tonically active neurons (TANs) have rarely been reported in the rodent, the inhibitory and mixed responses correspond to previously reports in the macaque accumbens of tonically active neurons with activity correlated with reward delivery and, following conditioning, to sensory stimuli associated with rewards. Eighteen of the 43 tonically active accumbens neurons showed spatial selectivity, i.e., behaviorally correlated increases or decreases in firing rate were of different magnitudes at the respective reward boxes. This is the first demonstration that the configuration of environmental sensory cues associated with reward sites are also an effective stimulus for these neurons and that different neurons are selective for different places. These results are consistent with a role for the nucleus accumbens in the initiation of goal-directed displacement behaviors.

Animals↗
PubMed2003

Reward value invariant place responses and reward site associated activity in hippocampal neurons of behaving rats.

To investigate the involvement of the hippocampal-accumbens system in goal-oriented displacement behaviors, hippocampal neuronal activity was recorded in rats learning and recalling new distributions of different volumes of liquid reward among the arms of a plus maze. Each arm had a reward box containing a water trough and identical visual cues that could be illuminated independently. As the water-restricted rat successively visited the respective boxes, it received 7, 5, and 3 drops of water, and then 1 drop, provided at 1-s intervals. (Reward distributions were reassigned daily and mid-session.) In the training phase, reward boxes were lit individually. In the recall phase, the lamps on all arms were lit and then turned off as the rat visited the boxes in order of descending value. Neuronal firing rates were analyzed for changes related to reward value or to shifts between learning and recall phases. The principal finding is that place responses remained unchanged after these manipulations and that these neurons showed no evidence of explicit coding of reward value. In addition, two other types of responses appeared while the rat was stationary at the reward boxes awaiting multiple rewards. These were observed primarily in neurons within the dentate gyrus, but also in CA1. Position-selective reward site responses were regular at 20-60 impulses per second, while position-independent discharges bursted irregularly at about 5 impulses per second. Such responses could explain controversial reports of reward dependence in hippocampal neurons. The higher incidence of the latter responses in the temporal ("ventral") hippocampus is consistent with the distinctive anatomical and functional properties of this subregion.

Action Potentials↗
PubMed2001

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: hippocampal pyramidal cells discharge selectively when the animal is in a certain 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 hippocampal 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 platform. To test for corresponding responses in head direction cells, three objects were equally spaced along the periphery of a circular platform. Preferred directions were measured before and after the group of objects was rotated. (The rat was disoriented in total darkness between sessions). This was repeated in the presence or absence of a cylinder enclosing the platform. When the enclosure was present, the preferred directions of all 30 cells recorded shifted by the same angle as the objects. In the absence of the enclosure, the preferred directions did not follow the objects, remaining fixed relative to the room. These results provide a possible neurophysiological basis for observations from psychophysical experiments in humans that background, rather than foreground, cues are preferentially used for spatial orientation.

Animals↗
PubMed2001

Position sensitivity in phasically discharging nucleus accumbens neurons of rats alternating between tasks requiring complementary types of spatial cues.

To determine how hippocampal location-selective discharges might influence downstream structures for navigation, nucleus accumbens neurons were recorded in rats alternating between two tasks guided respectively by lit cues in the maze or by extramaze room cues. Of 144 phasically active neurons, 80 showed significant behavioral correlates including displacements, immobility prior to, or after reward delivery, as well as turning, similar to previous reports. Nine neurons were position-selective, 22 were sensitive to task and platform changes and 40 others were both. Although the accumbens neurons showed the same behavioral correlate in two or four functionally equivalent locations, these responses were stronger at some of these places, evidence for position sensitivity. To test whether position responses were selective for room versus platform cues, the experimental platform was rotated while the rat performed each of the two tasks. This revealed responses to changes in position relative to both platform and room cues, despite the fact that previous studies had shown that place responses of hippocampal neurons recorded in the same task are anchored to room cues only. After these manipulations and shifts between the two tasks, the responses varied among simultaneously recorded neurons, and even in single neurons in alternating visits to reward sites. Again this contrasts with the uniformity of place responses of hippocampal neurons recorded in this same task. Thus accumbens position responses may derive from hippocampal inputs, while responses to context changes are more likely to derive from other signals or intrinsic processing. Considering the accumbens as a limbic-motor interface, we conclude that position-modulated behavioral responses in the accumbens may be intermediate between the allocentric reference frame of position-selective discharges in the hippocampus and the egocentric coding required to organize movement control. The conflicting responses among simultaneously recorded neurons could reflect competition processes serving as substrates for action selection and learning.

Animals↗
PubMed2001

Active locomotion increases peak firing rates of anterodorsal thalamic head direction cells.

Head direction (HD) cells discharge selectively in macaques, rats, and mice when they orient their head in a specific ("preferred") direction. Preferred directions are influenced by visual cues as well as idiothetic self-motion cues derived from vestibular, proprioceptive, motor efferent copy, and command signals. To distinguish the relative importance of active locomotor signals, we compared HD cell response properties in 49 anterodorsal thalamic HD cells of six male Long-Evans rats during active displacements in a foraging task as well as during passive rotations. Since thalamic HD cells typically stop firing if the animals are tightly restrained, the rats were trained to remain immobile while drinking water distributed at intervals from a small reservoir at the center of a rotatable platform. The platform was rotated in a clockwise/counterclockwise oscillation to record directional responses in the stationary animals while the surrounding environmental cues remained stable. The peak rate of directional firing decreased by 27% on average during passive rotations (r(2) = 0.73, P < 0.001). Individual cells recorded in sequential sessions (n = 8) reliably showed comparable reductions in peak firing, but simultaneously recorded cells did not necessarily produce identical responses. All of the HD cells maintained the same preferred directions during passive rotations. These results are consistent with the hypothesis that the level of locomotor activity provides a state-dependent modulation of the response magnitude of AD HD cells. This could result from diffusely projecting neuromodulatory systems associated with motor state.

Action Potentials↗
PubMed2000

Lesions of the medial shell of the nucleus accumbens impair rats in finding larger rewards, but spare reward-seeking behavior.

The goal of this study was to help better understand the importance of the nucleus accumbens (Nacc) in the processing of position and reward value information for goal-directed orientation behaviors. Sixteen male Long-Evans rats, under partial water deprivation, were trained in a plus-maze to find water rewards in the respective arms which were lit in pseudo-random sequence (training trials). Each day one reward arm was selected to deliver six drops of water (at 1 s intervals) the others provided only one drop per visit. After 32 visits, probe trials were intermittently presented among training trials. Here, all four arms were lit and offered the previously assigned reward. The rats rapidly learned to go to the highly rewarded arm. Six trained rats were given bilateral electrolytic lesions in the Nacc shell, two others had unilateral lesions and eight had sham operations (with approved protocols). Field potentials evoked by fornix stimulation were recorded in lesion electrodes to guide placements. Only the lesioned rats showed significant impairments (P<0.05) in selecting the greater reward on probe trials. However on training trials, lesioned (and sham-operated) rats made only rare errors. While the motivation to drink and the capacity for cue-guided goal-directed orientation behavior was spared, lesioned rats were impaired in learning the location of the larger reward. The accumbens lesions apparently impaired integration of position and reward value information, consistent with anatomical and electrophysiological data showing the convergence of hippocampal, amygdalar, ventral tegmental area (VTA) and prefrontal cortical inputs there.

Amygdala↗
PubMed2000

Position and behavioral modulation of synchronization of hippocampal and accumbens neuronal discharges in freely moving rats.

To understand how hippocampal signals are processed by downstream neurons, we analyzed the relative timing between neuronal discharges in simultaneous recordings in the hippocampus and nucleus accumbens of rats performing in a plus maze. In all, 154 pairs of cells (composed of 65 hippocampal and 56 accumbens neurons) were examined during the 1 s period prior to reward delivery. Cross-correlation analyses over a +/- 300-ms window with 10-ms bins revealed that 108 pairs had at least one significant histogram bin (P < 0.01). The most frequently occurring peaks of hippocampal firing prior to accumbens discharges appeared at latencies from -30-0 ms, corresponding to published values of the latency of the hippocampal pathway to the nucleus accumbens. Other peaks appeared most often at latencies multiples of about 110 ms prior to and after this, corresponding to theta rhythmicity. Since firing synchronization can result from several types of connectivity patterns (such as common inputs), a group of 18 hippocampus-accumbens pairs was selected as those most likely to have monosynaptic connections. The criterion was the presence of at least one highly significant peak (P < 0.001) at latencies corresponding to field potentials evoked in the accumbens by hippocampal stimulation. A significant peak occurred on all four maze arms for only one of these cell pairs, indicating positional modulation for the others. In addition, behavior dependence of the synchrony between these nucleus accumbens and hippocampus neurons was examined by studying data in relation to three different synchronization points: reward box arrival, box departure, and arrival at the center of the maze. This indicates that the functional connectivity between hippocampal and accumbens neurons was stronger when the rat was near reward areas. Ten of the hippocampal neurons in these 18 cell pairs showed 9-Hz (theta) rhythmic activity in autocorrelation analyses. Of these 10 cells, cross-correlograms from eight hippocampal-accumbens pairs also showed theta rhythmicity. Overall, these results indicate that the synchrony between hippocampus and nucleus accumbens neurons is modulated by spatial position and behavior, and theta rhythm may play an important role for this synchronization.

Animals↗
PubMed2000

Influence of conflicting visual, inertial and substratal cues on head direction cell activity.

In order to navigate efficiently, animals can benefit from internal representations of their moment-to-moment orientation. Head-direction (HD) cells are neurons that discharge maximally when the head of a rat is oriented in a specific ("preferred") direction in the horizontal plane, independently from position or ongoing behavior. This directional selectivity depends on environmental and inertial cues. However, the mechanisms by which these cues are integrated remain unknown. This study examines the relative influence of visual, inertial and substratal cues on the preferred directions of HD cells when cue conflicts are produced in the presence of the rats. Twenty-nine anterior dorsal thalamic (ATN) and 19 postsubicular (PoS) HD cells were recorded from 7 rats performing a foraging task in a cylinder (76 cm in diameter, 60 cm high) with a white card attached to its inner wall. Changes in preferred directions were measured after the wall or the floor of the cylinder was rotated separately or together in the same direction by 45 degrees, 90 degrees or 180 degrees, either clockwise or counterclockwise. Linear regression analyses showed that the preferred directions of the HD cells in both structures shifted by approximately =90% of the angle of rotation of the wall, whether rotated alone or together with the floor (r2>0.87, P<0.001). Rotations of the floor alone did not trigger significant shifts in preferred directions. These results indicate that visual cues exerted a strong but incomplete control over the preferred directions of the neurons, while inertial cues had a small but significant influence, and substratal cues were of no consequence.

Animals↗
PubMed1999

Hippocampal neuronal position selectivity remains fixed to room cues only in rats alternating between place navigation and beacon approach tasks.

To study the relationship between brain representations and behaviour, we recorded hippocampal neuronal activity in rats repeatedly alternating between two different tasks on a circular platform with four reward boxes along the edge. In the beacon approach task, rewards were provided only at the pair of diametrically opposite boxes that was illuminated. In the place navigation task, rewards were available only at the boxes positioned near the north-east and south-west corners of the room. Performance levels were high and rats rapidly reoriented to changes in lamp cues in the beacon approach task. Neuropsychological studies show that rats with hippocampal lesions readily employ beacon approach strategies, while place navigation is severely impaired. Previous studies suggested that the neurons might change their behavioural correlates as the rat performed the respective tasks. However, of 34 hippocampal 'place cells' recorded, all showed position selectivity fixed with respect to room cues, even in the beacon approach task where coding the position of the rat in the room was of no use for locating rewards. Whether or not hippocampal signals are actually employed for ongoing behaviour would then be decided by structures downstream from the hippocampus. If this is the case, then the 'counterproductive' room referred place-related discharges in the beacon approach task would be a background representation. This would provide support for proposals of multiple memory systems underlying different types of information processing and contrasts with the popular notion that local neuronal activity levels are selectively increased to the degree that the brain region is required for the ongoing function.

Acoustic Stimulation↗
PubMed1998

Discharge correlates of hippocampal complex spike neurons in behaving rats passively displaced on a mobile robot.

This study investigated location-, movement-, and directional-selectivity of action potential discharges of hippocampal neurons in awake rats subjected to passive displacements in order to estimate vestibular contributions to this activity. Water-deprived rats were habituated to being restrained in a sling mounted on a moving robot. The extracellular activity of single complex-spike cells in area CA1 of the hippocampus was recorded with glass micropipettes in the rats during passive translations, rotations, and immobility. The robot made a standardized series of trajectories starting from each of four corners of a square enclosure surrounded by black curtains. A drop of water was delivered to the rat each time the robot arrived at one designated corner of the arena. The activities of 29 neurons were investigated in 45 recording sessions (16 of which were in total darkness) in four rats. Hippocampal neurons recorded in 31 sessions (9 sessions in the dark) had significant location-selective increases or decreases in firing rate as the rat was passively displaced or immobile within the experimental arena. In 20 sessions (6 in the dark) direction-selective discharges were found when the rat was in the corners. In six sessions, cells discharged selectively during movement initiation or termination. These data suggest that information essential for path integration is present in the hippocampus and that inertial cues could play a vital role in hippocampal spatial functions. These results resemble those of O'Mara et al. ([1994] J Neurosci 14:6511) using the same protocol in macaques, suggesting similarities in hippocampal processing and function.

Action Potentials↗
PubMed1997

Biologically based artificial navigation systems: review and prospects.

Diverse theories of animal navigation aim at explaining how to determine and maintain a course from one place to another in the environment, although each presents a particular perspective with its own terminologies. These vocabularies sometimes overlap, but unfortunately with different meanings. This paper attempts to define precisely the existing concepts and terminologies, so as to describe comprehensively the different theories and models within the same unifying framework. We present navigation strategies within a four-level hierarchical framework based upon levels of complexity of required processing (Guidance, Place recognition-triggered Response, Topological navigation, Metric navigation). This classification is based upon what information is perceived, represented and processed. It contrasts with common distinctions based upon the availability of certain sensors or cues and rather stresses the information structure and content of central processors. We then review computational models of animal navigation, i.e. of animats. These are introduced along with the underlying conceptual basis in biological data drawn from behavioral and physiological experiments, with emphasis on theories of "spatial cognitive maps". The goal is to aid in deriving algorithms based upon insights into these processes, algorithms that can be useful both for psychobiologists and roboticists. The main observation is, however, that despite the fact that all reviewed models claim to have biological inspiration and that some of them explicitly use "Cognitive Map"-like mechanisms, they correspond to different levels of our proposed hierarchy and that none of them exhibits the main capabilities of real "Cognitive Maps"--in Tolman's sense--that is, a robust capacity for detour and shortcut behaviors.

Animals↗
PubMed1996

Place- and behavior-independent sensory triggered discharges in rat hippocampal CA1 complex spike cells.

To test for access of spatial cues to the hippocampus of unrestrained animals, single unit recordings of CA1 complex spike cells were made in thirsty rats as they made alternating visits between the center and corners of an enclosed 60 x 60 cm square arena. At intervals, all lights were turned off in the arena and it was rotated. Although no neuronal discharge activity was found that encoded the rotation angle, 11 of 97 neurons were selectively activated after lights were turned off or on. This activity began at delays of up to several seconds and persisted for tens of seconds. These discharges had no location selectivity or behavioral correlates and continued even as the rat performed several behaviors in different parts of the arena. This confirms similar results in restrained rabbits while showing for the first time that this neuronal activity can be independent of place and behavior. In addition this shows that sensory stimuli can trigger hippocampal discharges even when the rat is not required to make any behavioral responses to them.

Animals↗
PubMed1996

Spatial, behavioral and sensory correlates of hippocampal CA1 complex spike cell activity: implications for information processing functions.

The aim of this review is to better understand hippocampal function drawing almost entirely from single unit recording studies of pyramidal cells in areas CA1 and CA3 of behaving animals. Hippocampal location-selectivity ("place cell activity") as well as place-independent behavioral correlates and sensory-triggered discharges are demonstrated to have common features: (1) abstraction, that is, development within the hippocampal circuit of novel, cue-invariant supramodal representations; (2) varying degrees of generalization or specificity; (3) capacity for abrupt changes in discharge correlates of individual neurons as the animal changes its behavior pattern or its environment changes dramatically; (4) though individual neurons discharge when the subject occupies a certain place, or performs a certain behavior, the ensemble of hippocampal neurons comprehensively represent the whole environment and all behaviors required for the task at hand. A concordance is proposed: hippocampal neuronal discharge correlates represent elements partitioned from information abstracted along one or more systems of categorization or "information domains": the physical structure of the environment, regularities in the behavioral exigencies of the current situation. (Sensory stimuli can be considered as temporally varying features of the environment) Location-selectivity and behavioral correlates are extreme cases, and mixed correlates occur. The hippocampus is proposed to carry out several fundamental processes that transform information: abstraction, partitioning and recombination, that is, formation of conjunctive associations between events. Simultaneously activated neurons could then promote extrahippocampal associations linking together the diverse brain regions at the origin of these signals.

Animals↗
PubMed1995

Place-independent behavioural correlates of hippocampal neurones in rats.

The broad diversity of discharge correlates of hippocampal neurones has provoked controversy. For example, purported behavioural correlates could, instead, be location selectivity (of 'place cells') that is secondarily modulated by sensory stimulation or ongoing movements. In rats trained to perform identical behaviours in four corners of a symmetrical arena, we found hippocampal pyramidal cells discharged selectively as the rats performed task-related behaviours regardless of spatial location. Since the ensemble of these hippocampal neurones comprehensively represented all stages of the task, we propose that each cell represents an element of the temporal organization of the animal's behaviour, complementing the place cell representations of elements of the structure of the environment.

Action Potentials↗
PubMed1995

Inertial, substratal and landmark cue control of hippocampal CA1 place cell activity.

Hippocampal 'place cells' discharge when a rat occupies a location that is fixed in relation to environmental landmarks. A principal goal of this study was to determine whether hippocampal place cell activity could be influenced by inertial cues. Water-deprived rats were trained in a square-walled open field in a dark room. The behavioral task required alternating visits to water reservoirs in the centre and in the four corners of the arena. The rat and arena were rotated in total darkness through +/-90, 180 or 270 degrees C. The next water reward was then presented in the corner at the same position relative to the outside room as before the rotation. A cue card was later illuminated in this corner as a visual cue for the extra-arena (room) reference frame. Fifteen out of 97 recorded hippocampal CA1 complex spike cells had spatially selective discharges in non-central parts of the arena. After arena rotations, the firing fields of three units shifted between corners of the arena to maintain a fixed orientation relative to the room. This indicates that the hippocampus updated its representation of the position and heading direction of the rat using vestibular-derived inputs concerning rotation angle. Other spatially selective discharges were guided to landmark cues (cue card or position of the reward: two units) or arena-locked 'substratal' cues (eight units). In six cells, place cell activity suddenly ceased or appeared following rotations. These results provide evidence for contributions of inertial as well as substratal and landmark information to hippocampal spatial representations.

Animals↗