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The Journal of Neuroscience, October 31, 2007, 27(44):11888-11895; doi:10.1523/JNEUROSCI.1835-07.2007

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Behavioral/Systems/Cognitive
Dissociable Performance on Scene Learning and Strategy Implementation after Lesions to Magnocellular Mediodorsal Thalamic Nucleus

Anna S. Mitchell, Mark G. Baxter, and David Gaffan

Department of Experimental Psychology, Oxford University, Oxford OX1 3UD, United Kingdom

Correspondence should be addressed to Dr. Anna S. Mitchell, Department of Experimental Psychology, Oxford University, South Parks Road, Oxford, OX1 3UD, United Kingdom. Email: anna.mitchell{at}psy.ox.ac.uk

Monkeys with aspiration lesions of the magnocellular division of the mediodorsal thalamus (MDmc) are impaired in object-in-place scene learning, object recognition, and stimulus-reward association. These data have been interpreted to mean that projections from MDmc to prefrontal cortex are required to sustain normal prefrontal function in a variety of task settings. In the present study, we investigated the extent to which bilateral neurotoxic lesions of the MDmc impair a preoperatively learnt strategy implementation task that is impaired by a crossed lesion technique that disconnects the frontal cortex in one hemisphere from the contralateral inferotemporal cortex. Postoperative memory impairments were also examined using the object-in-place scene memory task. Monkeys learnt both strategy implementation and scene memory tasks separately to a stable level preoperatively. Bilateral neurotoxic lesions of the MDmc, produced by 10 x 1 µl injections of a mixture of ibotenate and NMDA did not affect performance in the strategy implementation task. However, new learning of object-in-place scene memory was substantially impaired. These results provide new evidence about the role of the magnocellular mediodorsal thalamic nucleus in memory processing, indicating that interconnections with the prefrontal cortex are essential during new learning, but are not required when implementing a preoperatively acquired strategy task. Thus, not all functions of the prefrontal cortex require MDmc input. Instead, the involvement of MDmc in prefrontal function may be limited to situations in which new learning must occur.

Key words: mediodorsal thalamus; strategy; episodic memory; amnesia; monkey; prefrontal cortex

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Received April 23, 2007; revised Aug. 10, 2007; accepted Sept. 5, 2007.

Correspondence should be addressed to Dr. Anna S. Mitchell, Department of Experimental Psychology, Oxford University, South Parks Road, Oxford, OX1 3UD, United Kingdom. Email: anna.mitchell{at}psy.ox.ac.uk

This article has been cited by other articles:

				A. S. Mitchell, P. G. F. Browning, C. R. E. Wilson, M. G. Baxter, and D. Gaffan Dissociable Roles for Cortical and Subcortical Structures in Memory Retrieval and Acquisition J. Neurosci., August 20, 2008; 28(34): 8387 - 8396. [Abstract] [Full Text] [PDF]

				M. G. Baxter, P. G.F. Browning, and A. S. Mitchell Perseverative interference with object-in-place scene learning in rhesus monkeys with bilateral ablation of ventrolateral prefrontal cortex Learn. Mem., March 1, 2008; 15(3): 126 - 132. [Abstract] [Full Text] [PDF]

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