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J M Pearce

Publications and source records attributed to J M Pearce.

At least 55 records · Page 3Linked to original sources
PubMed1999

Blocking in the Morris swimming pool.

Four experiments demonstrate that spatial blocking is governed by the same principles that govern blocking in Pavlovian conditioning. In the 2nd stage of each experiment, rats escaped from a Morris swimming pool by swimming to a submerged platform with a beacon attached to it. Test trials were then conducted in the absence of the platform and the beacon to assess the extent to which subjects had learned about the position of the platform with reference to the room cues. For the 1st stage of their training, rats either swam to the platform and beacon in the presence of curtains that prevented the room cues from being seen (Experiments 1 & 2), or they swam to the platform and beacon that were moved from trial to trial (Experiments 3 & 4). In each experiment, learning about the room cues in the 2nd stage of the experiment was blocked by the presence of the beacon. This blocking effect was disrupted by changing the appearance of the beacon for the 2nd stage of training or by restricting the amount of exposure to the beacon during the 1st phase of training.

Animals↗
PubMed1998

Hippocampal lesions disrupt navigation based on cognitive maps but not heading vectors.

Animals can find a hidden goal in several ways. They might use a cognitive map that encodes information about the geometric relationship between the goal and two or more landmarks. Alternatively, they might use a heading vector that specifies the direction and distance of the goal from a single landmark. Rats with damage to the hippocampus have difficulty in finding a hidden goal. Here we determine which of the above strategies is affected by such damage. Rats were required to swim in a water maze to a submerged platform, which was always at the same distance and direction from a landmark. The platform and landmark remained in the same place for the four trials of each session, but they were moved to a new position at the start of a session. Rats with damage to the hippocampus found the platform more efficiently than did normal rats in the first trial of a session but, in contrast to normal rats, their performance did not improve during a session. Our results indicate that hippocampally damaged rats are able to navigate by means of heading vectors but not cognitive maps.

Animals↗
PubMed1998

Lithium visibility in rat brain and muscle in vivo by 7Li NMR imaging.

The apparent concentration of lithium (Li) in vivo was determined for several regions in the brain and muscle of rats by 7Li NMR imaging at 4.7 T with inclusion of an external standard of known concentration and visibility. The average apparent concentrations were 10.1 mM for muscle, and 4.2-5.3 mM for various brain regions under the dosing conditions used. The results were compared to concentrations determined in vitro by high-resolution 7Li NMR spectroscopy of extracts of brain and muscle tissue from the same rats. The comparison provided estimates of the 7Li NMR visibility of the Li cation in each tissue region. Although there was considerable scatter of the calculated visibilities among the five rats studied, the results suggested essentially full visibility (96%) for Li in muscle, and somewhat reduced visibility (74-93%) in the various brain regions.

Animals↗