Characterization of hippocampal firing patterns during conditional discrimination and reversal

Recent evidence suggests that spatially-selective hippocampal neurons (place cells) show differential firing patterns depending on task requirements. The aim of the current project is to investigate the nature of discriminitive firing patterns during a tactile-spatial conditional discrimination task and its reversal.

The conditional discrimination task (left portion of the image) and reversal (right). The rat learns to select the left reward arm in the presence of the wood insert and the right reward arm in the presence of the textured plastic insert. In reversal (right), the rat must now suppress the old rule and reverse the response contingency.

Cortico-limbic interactions during suppression of a learned response

Modification of established behavioral patterns is dependent upon areas of the medial prefrontal cortex (mPFC). It has become clear in recent years that interactions between the hippocampus and mPFC not only occur, but may also be crucial for working memory performance. The current project will involve a combination of inactivation and recording techniques to investigate precisely how the mPFC and hippocampus interact during a switch from a nonmatching-to-place spatial task to a match-to-place strategy.

Single unit recording

In the Griffin Lab, we simulateously record from multiple single neurons using a recording microdrive, which contains 16 independently-movable tetrodes, allowing precise localization of an optimal recording site. This technique enables us to record up to 50-100 neurons simulataneously in awake behaving animals.

Microinfusion techniques

Through implantation of small infusion cannula, we also have the ability to deliver pharmacological agents directly into discrete brain structures. This technique enables us to create a "reversible lesion" and compare behavioral and neural activity under the influence of the drug and the absence of the drug in the same animal. We are currently using this technique in combination with recordings to investigate the behavioral correlates of neuronal firing patterns before and after inactivation of related brain structures.