Functional Correlates of Rodent Visual Cortex Organization: ABehavioral and Neuroanatomical Study of Individual Differences inthe Gerbil Visual System Open Access

Abstract

Abstract

Functional Correlates of Rodent Visual Cortex Organization: A Behavioral and Neuroanatomical Study of Individual Differences in the Gerbil Visual System

By Magdalena Krysiak

Rodents are ideal subjects for the study of comparative relationships between brain and behavior, particularly in comparison to Primates. They are small, easily obtainable and trainable, and inhabit a wide range of ecological niches. In this project, we characterized the visual behavior of individual Mongolian gerbils ( Meriones unguiculatus) using two kinds of tests - measuring both depth perception and acuity - and asked whether these functional measures correlate with measurements of the structural complexity of the visual system. Gerbil posterior cortex contained a distinct primary visual cortex (V1) and a heavily myelinated area similar in location to ground squirrel TP, which is involved in visual motion perception. As expected, the relative expanse of V1 was positively correlated with acuity, and the relative expanse of proto-TP was positively correlated with speed of performance on the jumping stand, implying a role in depth perception and strengthening the case for an evolutionarily conserved visuomotor region. Contrary to our expectations, lower light levels did not decrease performance on the acuity task, and significantly decreased latency on the jumping stand (a trend driven by less day-active animals). Better performance in low light suggests that the cone system in this species is not as well defined and/or behaviorally relevant as previously thought. It is suggested that future behavioral studies performed on nocturnal species should consider how light preference could affect performance. Overall, the results support the value of a comparative approach utilizing within-species individual differences to help understand brain-behavior relationships.

Table of Contents

Table of Contents Introduction...........................................................................................1 Overview...............................................................................................1 Impetus and Implications..........................................................................3 Comparative Analysis and the Case for Studying Individual Differences..............4 Visual Cortex..........................................................................................6 Cross-Species Neuroanatomical Comparisons...............................................7 Gerbil Ecology.........................................................................................8 Previous Studies of Gerbil Visual Behavior.....................................................9 The Current Experiment..........................................................................12 Predictions............................................................................................13 Methods...............................................................................................15 Overview..............................................................................................15 Animals.................................................................................................15 Behavioral Testing..................................................................................16 Luminance Levels...................................................................................16 Jumping stand.......................................................................................16 Background surface................................................................................17 Training................................................................................................18 Testing.................................................................................................18 Acuity..................................................................................................19 Training................................................................................................20 Testing.................................................................................................21 Activity Levels........................................................................................21 Neuroanatomy.......................................................................................23 Results..................................................................................................26 Behavior................................................................................................26 Jumping Stand........................................................................................26 Acuity Apparatus.....................................................................................27 Activity Levels........................................................................................28 Neuroanatomy.......................................................................................30 Brain-Behavior Correlations.......................................................................31 Other Observations.................................................................................32 Discussion..............................................................................................34 Behavior................................................................................................34 The jumping stand...................................................................................34 Comparison to previous gerbil studies......................................................... 37 Acuity...................................................................................................39 Neuroanatomical Findings..........................................................................40 ActivityLevels.........................................................................................43 Development and evolution........................................................................43 Conclusion..............................................................................................44 References.............................................................................................46 Appendix................................................................................................51 List of Figures Images Figure 1. Examples of visual cortex organization.... .......................................51 Figure 2. A schematic diagram of the jumping stand...................................... 52 Figure 3. Picture of the jumping stand in the current study............................ 52 Figure 4. Picture of the background image................................................... 53 Figure 5. A cut-away schematic of the acuity apparatus............................... 54 Figure 6. Picture of the acuity apparatus built for our study........................... 54 Figure 7. Example sections... distinctiveness of area proto-TP........................ 55 Figure 8. Example sections..... compartmentalization of area V1...................... 55 Figure 9. A representative flatmount section of gerbil cortex.......................... 56 Figure 10. An example section with outlines................................................. 57 Graphs Figure 11. Jumping stand accuracy as a function of distance.......................... 58 Figure 12. Jumping stand accuracy across light levels.................................... 58 Figure 13. Jumping stand latency as a function of distance............................. 59 Figure 14. Jumping stand latency across light level........................................ 59 Figure 15. Acuity across light level..............................................................60 Figure 16. Interaction of latencies across light levels and activity level..............60

Figure 17. Correlation between activity level and latency in the dark................ 61 Figure 18. Quadratic interaction between acuity at different light levels.............61 Figure 19. Correlation between average acuity threshold and average latency.... 62 Figure 20. Correlation between trials to criterion and percent accuracy............. 62 Figure 21. Correlation between trials to criterion and average latency............... 63 Figure 22. Correlation between trials to criterion and average latency............... 63 Figure 23. Correlation between trials to criterion and average acuity thresholds.. 64 Figure 24. Correlation between normalized are of proto-TP and average latency...64 Figure 25. Interaction between latency across distance and area of proto-TP..... 65 Figure 26. Correlation between the normalized area of V1 and acuity................ 65 Figure 27. Correlation between average activity level and proto-TP.................. 66 Figure 28. Correlation between average activity level and V1.......................... 66

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School	Laney Graduate School
Department	Psychology
Degree	MA
Submission	Dissertation
Language	English
Research Field	Biology, Neuroscience Psychology, Behavioral Psychology, Experimental
Keyword	animal behavior V1 TP depth perception acuity jumping stand
Committee Chair / Thesis Advisor	Rodman, Hillary R, Emory University
Committee Members	Neill, Darryl B, Emory University Lourenco, Stella, Emory University Hampton, Robert, Emory University

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