Dynamics of memory-related spatial tuning in the frontal eye fields
R.L. White*; L.H. Snyder
Dept Anatomy & Neurobiology, Washington University, St Louis, MO, USA
Neurons in the frontal eye field (FEF) are critical for the planning and execution of saccades. Some FEF neurons demonstrate persistent activity during the delay period preceding a memory-guided saccade. This activity might play a role in maintaining spatial memories and/or producing memory-guided behavior. The dynamics of delay period activity are likely to provide important clues to our understanding of the neural substrate of spatial memory.

Attractor network models of spatial memory predict that excitatory connections between similarly tuned neurons are capable of driving an ensemble of neurons in the absence of external input. In such models, stored information degrades over time. A manifestation of such degradation is seen in the precision of memory-guided saccadesthese saccades are more variable the longer a subject must remember a targets location. The neural correlates of this behavior have not been clearly identified. We asked whether the spatial fidelity of FEF activity degrades over time, and if so, exactly what form this degradation takes.

In two monkeys, the spatial information conveyed by individual FEF neurons decreased over time. The decrease in information was likely mediated by changes in the tuning of individual neurons and in the trial-to-trial reliability of their firing. Multiunit and single unit tuning were highly correlated. A third animal showed a different pattern of neuronal activity. This animal, trained extensively on a much more difficult spatial memory task (Baker et al. 2003), showed similar behavioral degradation as the other two animals, but no degradation in neuronal spatial information. This pattern of results suggests that animals may employ different strategies that rely to varying degrees on FEF neural activity to guide oculomotor behavior in a spatial working memory task.

Support Contributed By: NEI; McDonnell & EJLB Foundations

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