Alterations of Performance on an Attentional Task Following Manipulations of the Ventromedial Thalamic Nucleus in the Rat Open Access

McGee, Jennifer Marie-Juergensen (2014)

Permanent URL: https://etd.library.emory.edu/concern/etds/6t053g263?locale=en
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Abstract

It is not yet understood how an organism brings together motivational and sensorimotor information to make decisions on how to respond to contingencies in their environment. Previous research suggests a pivotal role of the basal ganglia in integrating this information yet one major output of the basal ganglia, the ventromedial nucleus of the thalamus (VMT), has been largely ignored. The goal of the present study was to determine the role of the VMT in a complex test of attention in rodents, the 5-choice serial reaction time test (5-CSRTT). Primary findings were that bilateral lesions of the VMT resulted in an increased performance (as measured by an increase of accuracy, a decrease in omissions and extraneous responding) and increased time to retrieve the food reward. Further, transient deactivation using three doses of the GABAA receptor agonist muscimol resulted in a mix of responses, in particular an increase in impulsivity (as measured by an increase in premature responding). Other manipulations failed to produce a statistically significant change in behavior. We hypothesize that the lesions may have inadvertently destroyed other axons of passage, causing either motoric or motivational aberrations. The finding that muscimol increases impulsivity adds to the existing literature that has already implicated a role of the basolateral amygdala, striatum, basal ganglia and frontal cortices; four regions that are strongly connected to the VMT.

Table of Contents

Introduction................................................1

Thalamus...................................................1

Basal Ganglia...............................................2 Limbic System.............................................5

Functional Significance..................................7

5-CSRTT.....................................................9 Summary...................................................11

Method......................................................12

Materials and Methods: VMT lesions................12

Materials and Methods: Drug injections............17

Results.......................................................21

Histology.....................................................22

Percent correct............................................22 Omissions....................................................24 Premature responding....................................26 Perseverative responding................................27 Time out responding......................................28 Total responding...........................................30

Latency measures.........................................31

Locomotor activity........................................32

Discussion....................................................32

Impact of muscimol injections.........................32

Muscimol vs electrolytic lesions and lidocaine.....35

Possible incentive salience connection...............38

Picrotoxin results...........................................39

Implications and future results.........................40

References...................................................45

Figure 1. Afferents and efferent of the ventromedial thalamus .....................................................65

Figure 2. Flowchart of possible trial sequences in the 5-CSRTT.....................................................66

Figure 3. 5-CSRTT training schedule .......................................................................................67

Figure 4. Graphical summary of changes in behavior relative to saline, given the stated treatments.....68

Figure 5. Percent correct before and after surgery, divided by lesion and sham groups......................69

Figure 6. Errors of omission before and after surgery, divided by lesion and sham groups....................70

Table 1. Means of Responses on Each Measure of the 5-CSRTT by Drug and Dose............................71

Table 2. Means of Responses on Each Measure of the 5-CSRTT by Drug and Dose............................72

Figure 7. Results on the 5-CSRTT after 20 ng of muscimol ...........................................................73

Table 3. Mean Latency Data for Correct Responses, Incorrect Responses, and

Time to Retrieve the Reward in Seconds for Rats with VMT Lesions, Before and

After Surgery (with Standard Deviations in Parentheses)..............................................................74

Figure 8. Average latencies to a correct response, to retrieve the food reward,

and to an incorrect response, before and after surgery. ..............................................................75

Figure 9. Cortical projections of the sub-regions of the VM...........................................................76

Figure 10. Placement of cannulae............................................................................................77

Figure 11. Location of lesions.................................................................................................78


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