Dissertation
Investigating the cerebellar contribution to categorization
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2025
DOI: 10.25820/etd.008103
Abstract
The cerebellum is as functionally complex as it is anatomically intricate. Historically, it was believed to be primarily a motor structure, involved in motor learning and motor planning. However, research involving patients who suffered from cerebellar stroke or other cerebellar-related conditions revealed cognitive deficits, which challenged this view. Subsequent studies found that the location of lesions within the cerebellar cortex determined the type of symptoms (motor or cognitive) a person experienced, suggesting functional specialization within the cerebellum. Notably, cerebellar damage that resulted in cognitive deficits often projected to one of the three major output regions of the cerebellum, the lateral cerebellar nuclei (LCN). To further investigate the cognitive role of the cerebellum, we employed a rodent model and rule-based (RB) categorization tasks. Categorization is a cognitive process that allows organisms to form equivalence classes based on perceptual or functional similarity and involves executive functions such as selective attention, memory, and decision-making. The experiments described in this thesis represent the first investigation of cerebellar involvement in categorization using a rodent model. Using a touchscreen apparatus, rats were trained on categorization paradigms with stimuli and procedures analogous to those used in human studies. Rats categorized visual stimuli that varied along two dimensions (i.e., spatial frequency and orientation of black-and-white gratings). RB category learning required the rats to categorize based on one relevant dimension while ignoring the other. In Chapter 2, we found that LCN-lesioned rats took longer to reach criterion and exhibited lower accuracy throughout training compared to sham controls. Furthermore, lesioned rats showed greater difficulty adapting when the categorization rule was switched, taking longer to reach criterion under the new rule compared to the first rule. Computational modeling indicated that LCN-lesioned rats were generally less engaged with the task and switched between engagement states more frequently than sham controls. In Chapter 3, we used a chemogenetic approach to inhibit and excite the LCN early in training. Inhibition of the LCN replicated the findings from Chapter 2, where rats required more time to reach criterion and displayed reduced overall accuracy. Excitation of the LCN, a novel approach, facilitated category learning. Excitation of the LCN resulted in rats reaching criterion faster and showing higher overall accuracy than the control group. After reaching criterion, all rats underwent a retention test. Inhibition had no effect on retention performance, suggesting that the cerebellum plays a critical role during the early stages of learning but has limited influence once learning has been consolidated. Future experiments are proposed to further elucidate the role of the cerebellum in categorization.
Details
- Title: Subtitle
- Investigating the cerebellar contribution to categorization
- Creators
- Shannon L. Wachter
- Contributors
- John H. Freeman (Advisor)Krystal L. Parker (Committee Member)Ryan LaLumiere (Committee Member)Jason Radley (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Psychology
- Date degree season
- Summer 2025
- DOI
- 10.25820/etd.008103
- Publisher
- University of Iowa
- Number of pages
- xi, 105 pages
- Copyright
- Copyright 2025 Shannon L. Wachter
- Language
- English
- Date submitted
- 07/16/2025
- Description illustrations
- Illustrations, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 90-105).
- Public Abstract (ETD)
Although it constitutes a small portion of the total brain volume, the cerebellum supports many essential functions. Previous research has primarily focused on its role in motor movements and motor planning, areas where the cerebellum plays a significant part. However, recent studies involving human patients with cerebellar damage suggest that the cerebellum may also contribute to higher cognitive processes. This involvement may stem from its communication with forebrain structures through the lateral cerebellar nuclei (LCN), a major cerebellar output zone. To examine cerebellar contributions to cognition, we utilized a rule-based (RB) categorization paradigm. Categorization is a cognitive process that allows organisms to form equivalence classes based on perceptual or functional similarity. It engages multiple executive functions, including selective attention, memory, and decision-making. The experiments described in this thesis represent the first investigation of cerebellar involvement in categorization using a rodent model. Using a touchscreen apparatus, rats were trained on categorization tasks with procedures and stimuli comparable to those used in human research. In Chapter 2, we laid the foundation for understanding the cerebellum s role in category learning by lesioning the LCN. We found that the LCN is critical for accurate category learning and for maintaining the appropriate strategy during the task. Additionally, our findings suggest that the cerebellum may play a role in cognitive flexibility. In Chapter 3, we inhibited the LCN early in learning and replicated the results from Chapter 2. Furthermore, we enhanced the likelihood of LCN activation and observed faster category learning and greater overall engagement with the task. Future experiments are proposed to further explore the cerebellum's role in cognitive processing and extend this line of research.
- Academic Unit
- Psychological and Brain Sciences
- Record Identifier
- 9984948238702771
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