Unpredictable mealtimes rather than social jetlag affects acquisition and retention of hippocampal dependent memory.

Some degree of circadian rhythm disruption is hard to avoid in today's society. Along, with many other deleterious effects, circadian rhythm disruption impairs memory. One way to study this is to expose rats to daylengths that are outside the range of entrainment.

Lesions to the lateral mammillary nuclei disrupt spatial learning in rats.

The head direction (HD) signal is thought to originate in the reciprocal connections between the dorsal tegmental nuclei (DTN) and the lateral mammillary nuclei (LMN) and lesions to these structures disrupt the HD signal in downstream structures. Lesions to the DTN also disrupt performance on spatial tasks where directional heading is thought to be important. In Experiment 1, rats with bilateral electrolytic lesions of the LMN and sham controls were trained on 2 tasks previously shown to be sensitive to DTN damage.

Locus Coeruleus Optogenetic Light Activation Induces Long-Term Potentiation of Perforant Path Population Spike Amplitude in Rat Dentate Gyrus.

Norepinephrine (NE) in dentate gyrus (DG) produces NE-dependent long-term potentiation (NE-LTP) of the perforant path-evoked potential population spike both and . Chemical activators infused near locus coeruleus (LC), the source of DG NE, produce a NE-LTP that is associative, i.e.

Consistent meal times improve performance on a daily time-place learning task.

The ability of an animal to learn the spatiotemporal variability of stimuli is known as time-place learning (TPL). The present study investigated the role of the food-entrainable oscillator (FEO) in TPL. Rats were trained in an operant conditioning chamber which contained two levers that distributed a food reward, such that one lever provided food rewards in morning sessions, while the other lever provided food rewards in afternoon sessions.

Rats in a levered T-maze task show evidence of time-place discriminations in two different measures.

It is difficult for rats to learn to go to an arm of a T-maze to receive food that is dependent on the time of day, unless the amount of food in each daily session is different. In the same task, rats show evidence of time-place discriminations if they are required to press levers in the arms of the T-maze, but learning is only evident when the first lever press is considered, and not the first arm visited. These data suggest that rats struggle to use time as a discriminative stimulus unless the rewards/events differ in some dimension, or unless the goal locations can be visited prior to making a response.

The effects of lesions to the postsubiculum or the anterior dorsal nucleus of the thalamus on spatial learning in rats.

To investigate the role of the head direction (HD) cell circuit in spatial navigation, rats with bilateral, neurotoxic lesions to the postsubiculum (PoS; Experiment 1) or the anterior dorsal nucleus of the thalamus (ADN; Experiment 2) were compared to sham controls on 2 tasks that could be solved using directional heading. Rats were first trained on a direction problem in a water T maze where they learned to travel either east or west from 2 locations in the experimental room. ADN lesioned rats were impaired relative to sham controls on the first block of 8 trials, but not on the total trials taken to reach criterion.

Mice use start point orientation to solve spatial problems in a water T-maze.

Behavioral work has demonstrated that rats solve many spatial problems using a conditional strategy based on orientation at the start point. The present study assessed whether mice use a similar strategy and whether the strategy would be affected by the poorer directional sensitivity of mice. In Experiment 1, mice were trained on a response, a direction or one of two place problems to locate a hidden platform in a water T-maze located in two positions.

In a daily time-place learning task, time is only used as a discriminative stimulus if each daily session is associated with a distinct spatial location.

It is difficult for rats to acquire daily time-place (TP) learning tasks. One theory suggests that rats do not use time of day as a stimulus signaling a specific response. In the present study, we tested rats' ability to use time of day as a discriminative stimulus.

Hippocampal spatial mapping and the acquisition of competing responses.

Response reversal learning is facilitated in many species, including humans, when competing responses occur in separate contexts. This suggests hippocampal maps may facilitate the acquisition of competing responses and is consistent with the hypothesis that contextual encoding permits rapid acquisition of new behaviors in similar environments. To test this hypothesis, the pattern of Arc expression was examined after rats completed a series of left/right response reversals in a T-maze.

The effects of bilateral lesions to the dorsal tegmental nucleus on spatial learning in rats.

The head-direction (HD) signal is believed to originate in the dorsal tegmental nucleus (DTN) and lesions to this structure have been shown to disrupt HD cell firing in other areas along the HD cell circuit. To investigate the role of the DTN in spatial navigation, rats with bilateral, electrolytic (Experiment 1), or neurotoxic (Experiment 2) lesions to the DTN were compared with sham controls on two tasks that differed in difficulty and could be solved using directional heading. Rats were first trained on a direction problem in a water T maze where they learned to travel either east or west from two locations in the experimental room.

Aversive, appetitive and flavour avoidance responses in the presence of contextual cues.

Appetitive, aversive and avoidance responses to a flavoured solution in distinct contexts were examined. Rats placed in either a white or black box were given access to saccharin. Consumption was followed by an injection of a toxin in one but not the other box.

Rats' orientation is more important than start point location for successful place learning.

Rats were trained to locate food on a plus maze that was moved between 2 locations. The food was in a fixed location relative to room cues but the maze, and the animals' start point, were either translated (shifted to the left or right) or rotated (by 90 degrees or 45 degrees ) across trials. Rats started from the same or different places solved the problem if they headed in a direction different from the start point.

The contribution of spatial cues to memory: direction, but not cue, changes support response reversal learning.

In four experiments, rats were trained on a response problem followed by three reversals. Rats that changed rooms between acquisition and reversals learned the reversals in fewer trials than rats that remained in the same room, even when distal visual cues were limited. Changes in orientation, even in the same room, also facilitated response reversal learning.

CA1 ischemic injury does not affect the ability of Mongolian gerbils to solve response, direction, or place problems.

Open field and T-maze paradigms are used to test the effects of hippocampal lesions on spatial memory in rodents. Place cells in the dorsal CA1 region of the hippocampus are known to be responsible for the formation of global place maps, while CA3 neurons respond to changes in local contexts. It is proposed here that when dorsal CA1 is selectively destroyed, gerbils will be unable to solve direction and place problems while context-dependent representations of relative maze positions should be spared since CA3 cells are left intact.

Location serves as a conditional cue when harp seals (Pagophilus groenlandicus) solve object discrimination reversal problems.

We examined the capacity of harp seals (Pagophilus groenlandicus) to use spatial context (i.e., their tank) as a conditional cue to solve a two-choice visual discrimination reversal task.

Where am I? Distal cues use requires sensitivity to start location change in the rat.

Place learning is impaired when a single plus maze is moved between adjacent locations 33-120 cm apart. This maze translation creates distinct start locations but maintains a single goal location with respect to distal cues. Hippocampal cell recording data suggest the majority of place fields are tied to apparatus boundaries, not to distal cues, when an apparatus is moved these distances to the left or right.

The effects of hippocampal lesions on response, direction, and place learning in rats.

Rats with hippocampal or sham lesions were trained to find food on a T maze located at 2 positions. Response rats were required to make a right or left turn. Direction rats were required to go in a consistent direction (east or west).

Perirhinal cortex lesions impair context aversion learning.

Rats with perirhinal cortex lesions were compared with sham controls on a conditional discrimination in which saccharin was paired with LiCl in context 1, but paired with saline in context 2. Perirhinal-lesioned rats were slightly slower to acquire the discrimination but reached control levels by the end of acquisition. Both groups showed transfer to familiar tap water, consuming less in context 1 than in context 2.

An analysis of response, direction, and place learning in an open field and T maze.

Rats were trained to locate food in a response, direction, or place problem on an open field located at 2 positions. In Experiment 1, both the response and direction groups solved the problem. The place group failed to solve the task in approximately 300 trials.