Date of Award

Spring 1999

Project Type

Dissertation

Program or Major

Psychology

Degree Name

Doctor of Philosophy

First Advisor

Robert G Mair

Abstract

Slow response speed has been associated with several neuropsychological disorders including Korsakoff's disease. The ability to respond to brief stimuli can be tested to assess whether slow response speed is due to slow stimulus processing. A seven choice serial reaction time task was developed to test the ability to respond to brief stimuli. Distractibility and stimulus discriminability were manipulated to challenge performance and cues were presented to enhance performance. In Experiment 1, six unlesioned rats were tested on this task. As expected, significant deficits were found when (1) stimulus duration was decreased, (2) bright distractor light was briefly presented, (3) a bright overhead fight was illuminated throughout the trial, and (4) when side cues were not given. Reaction time remained fairly consistent across all conditions although there was a significant increase when the bright overhead light was presented in the discrimination condition. These results are consistent with a previously used five choice serial reaction time task, and provide evidence that the current task may be useful for testing the ability to respond to brief stimuli.

In Experiment 2, presurgically trained rats were given lesions of the intralaminar nuclei (ILn), prefrontal cortex (PFC), or hippocampus (HP) or sham-control surgery, and then tested on the seven choice serial reaction time task. Generally, the results across all behavioral conditions showed a significant decrease in accuracy for the PFC group at brief stimulus durations compared to all other groups. It does not appear these results are due to disruption of motivation, debilitation following surgery, or an inability to perform the requirements of the task as all groups performed well when stimuli were presented for a long duration. Both PFC and ILn groups showed significantly slower reaction time across all behavioral conditions. The HP group was not significantly different from controls. The accuracy deficit for the PFC group is thought to reflect the disruption of scanning and/or speed of processing sensory information. The slow reaction time for PFC and ILn groups may indicate motor dysfunction due to disruption of cortico-basal ganglia-thalamo-cortical connections that are innervated in striatum by the ILn.

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