Biomedical subjects

Christina M Thorpe

Publications and source records attributed to Christina M Thorpe.

4 recordsLinked to original sources

PubMed2006

Rats' performance on an interval time-place task: increasing sequence complexity.

Rats were trained on an interval time-place learning (TPL) task in which the location of food availability depended on the time since the start of the session. Each of four levers (numbered 1, 2, 3, 4) provided food on an intermittent schedule for two nonconsecutive 3-min periods. The order in which the levers provided food was 1, 2, 4, 3, 2, 3, 1, 4. This order was consistent across sessions. Previous research conducted in our lab has shown that when only four "places" are used, rather than the eight in the present study, rats use a timing strategy to track the location of food. Pizzo and Crystal (2004) recently trained rats on an interval TPL in which each of eight arms of a radial arm maze provided food. They found evidence suggesting that rats used both spatial and temporal information. In the present study, in which a revisiting strategy was used (i.e., each lever provided food on more than one occasion), the rats tracked both the spatial and the temporal availability of food for the first half of the session. Interestingly, in the second half of the sessions, the rats appeared to be timing the availability of food even though they did not know where it would occur. That is, the rats knew the temporal, but not the spatial, contingencies for the second half of the session. It appears that the requirement of revisiting a previously reinforced lever resulted in rats' no longer being able to solve the spatial aspect of the task.

Animals↗

PubMed2005

Spatial associative memory: a possible species difference in rats and pigeons.

Previous research has shown that pigeons can remember which of four spatially distinct responses was last reinforced, for at least 72 h. The present study sought to replicate this finding using rats. Rats were tested in an operant chamber containing four spatially distinct levers. In each session one lever was randomly selected to provide reinforcement for 15 min. This reinforced period was preceded by a non-reinforced period that was 30s long, on average. During the non-reinforced period the amount the rat pressed on the previously reinforced lever was compared to responding on the other three levers, and was taken as a measure of memory. Sessions were separated either by 17 min, 24 or 72 h. Unlike pigeons, rats responded at chance levels following each of these retention intervals. This finding adds to previous research suggesting differences in cognitive processes in rats and pigeons.

Animals↗

PubMed2005

Interval time-place learning by rats: varying reinforcement contingencies.

Two experiments with rats were conducted to study interval time-place learning when the spatiotemporal contingencies of food availability were more similar to those likely to be encountered in natural environments, than those employed in prior research. In Experiment 1, food was always available on three levers on a variable ratio (VR) 35 schedule. A VR8 schedule was in effect on Lever 1 for 5 min, then on Lever 2 for 5 min, and so forth. While rats learned to restrict the majority of their responding to the lever that provided the highest density of reinforcement, they seemed to rely on a win-stay/lose-shift strategy rather than a timing strategy. In Experiment 2, the four levers provided food on variable ratios of 15, 8, 15, and 30, each for 3 min. As expected the rats learned these contingencies. A novel finding was that the rats had a spike in response rate immediately following a change from a higher to lower reinforcement density. It is concluded that rats exposed to spatiotemporal contingencies behave so as to maximize the rate of obtained reinforcement.

Animals↗

PubMed2004

Some pitfalls in measuring memory in animals.

Because the presence or absence of memories in the brain cannot be directly observed, scientists must rely on indirect measures and use inferential reasoning to make statements about the status of memories. In humans, memories are often accessed through spoken or written language. In animals, memory is accessed through overt behaviours such as running down an arm in a maze, pressing a lever, or visiting a food cache site. Because memory is measured by these indirect methods, errors in the veracity of statements about memory can occur. In this brief paper, we identify three areas that may serve as pitfalls in reasoning about memory in animals: (1) the presence of 'silent associations', (2) intrusions of species-typical behaviours on memory tasks, and (3) improper mapping between human and animals memory tasks. There are undoubtedly other areas in which scientists should act cautiously when reasoning about the status of memory.

Animals↗