Reversal Learning in Rhesus Macaques is impaired after Neonatal Perirhinal Lesions Open Access

White, Jessica Baijie (2016)

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Neonatal damage to the perirhinal (Neo-PRh) cortex in rhesus macaques impaired performance on working memory tasks with high proactive interference. To determine if this inability to overcome proactive interference was due to impaired stimulus-reward association learning or impaired behavioral flexibility, the same rhesus macaques (Neo-PRh) and age-matched sham-operated controls (Control) were tested using an abbreviated version of the Intradimensional/Extradimensional (ID/ED) Set Shifting task. The task consisted of successively acquiring two simple discrimination problems using colored shape stimuli, followed by three serial reversals requiring behavioral flexibility. Finally, a complex discrimination stage was given in which responses to the shape stimuli had to be maintained in the presence of a new set of line stimuli overlaid on the original shape stimuli. Adult monkeys with Neo-PRh lesions performed as well as control monkeys in all discrimination stages, but were impaired on the serial reversals. These findings indicate that neonatal PRh lesions in monkeys impaired the use of behavioral flexibility, but spared stimulus-reward association learning. Although this study confirmed an impairment in behavioral flexibility as a result of neonatal PRh lesions that may be at the source of their inability to overcome proactive interference, we cannot rule out that impaired performance in working memory tasks with high proactive interference might have also resulted from impaired cognitive flexibility. Future work will need to test this possibility by continuing the training the same Neo-PRh monkeys on the extradimensional shift (EDS) stage of the ID/ED task. In this stage, the previously attended stimuli (shapes) must be ignored and, instead, the previously ignored stimuli (lines) must be attended. This shift in attentional set requires the use of cognitive flexibility that might be essential to overcome proactive interference in working memory tasks.

Table of Contents

Introduction 1

Hypotheses 9

Methods 9

Subjects 9

Neuroimaging 10

Surgical Procedures 11

Lesion Assessment 12

Cognitive Testing 13

Initial training procedure 13

Intradimensional/Extradimensional set-shifting task (ID/ED) 13

Data Analysis 14

Discrimination Stages 15

Reversal Stages 15

Lesion Correlation 15

Results 16

Discrimination Stages 16

Reversal Stages 17

Lesion Correlation 18

Discussion 18

Discrimination learning stages 18

Reversal learning stages 19

Relevance to Neurological Disorders 20

References 22

Table 1 27

Figure 1 28

Figure 2 29

Figure 3 30

Figure 4 31

Figure 5. 32

Figure 6 33

Figure 7 34

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