Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Neuroscience
Supervisor
Diedrichsen, Jörn
Abstract
Previous studies of cerebellar function in humans have shown that it is activated by a myriad of tasks ranging from motor learning and language to working memory and more. These studies have prompted a deviation from the traditional view of the cerebellum as a purely motor structure. However, the precise contribution of the cerebellum to these tasks remains ambiguous.
A prevalent assumption in fMRI studies is interpreting BOLD activation as evidence of the cerebellum's involvement in specific tasks. However, this interpretation is potentially misleading, especially considering that the BOLD signal predominantly represents cerebellar input, with output activity largely absent. Consequently, observed activations in the cerebellum may merely reflect the transmission of signals via fixed anatomical connections with the neocortex, independent of any requisite cerebellar computations.
To circumvent this interpretative limitation, we present a novel framework. First, we take advantage of the diversity of tasks in a multi-domain task battery, proposing a \textbf{task-invariant model of cortico-cerebellar connectivity}. This model predicts cerebellar activation levels based on neocortical inputs. Building on this, we introduce the concept of \textbf{"selective recruitment"} to examine cerebellar-specific processes via functional MRI. Drawing insights from cerebellar patient studies, we validate this framework in the motor domain, demonstrating that the cerebellum's input is gated based on task requirements, with intensified activation at higher speeds.
Venturing into a more complex domain, we test the framework in a working memory task; A task with subtler deficits and inconclusive cerebellar patient study outcomes. We reveal that the cerebellum becomes selectively engaged during the encoding of substantial information loads, as demonstrated with six items in our task.
In sum, our approach of investigating selective cerebellar recruitment, particularly in areas where patient studies offer limited clarity, paves the way for a more holistic comprehension of the cerebellum's nuanced roles, enriching our appreciation of this intricate "little brain."
Summary for Lay Audience
Many think of the cerebellum, the so-called "little brain", as merely helping us move in a coordinated manner. But new studies suggest it is more versatile than we believed it to be, playing a role in understanding language, making decisions, social interactions, and even handling emotions. This revelation pushes us to rethink the myriad roles this small brain structure might hold in our daily lives. Yet, pinning down the exact role of cerebellum in these tasks has been a challenge.
In pursuit of finding cerebellar function, fMRI—a non-invasive imaging method to study brain activity—has shown that the cerebellum "lights up" in almost any tasks. However, the bright spots we see on fMRI images of the cerebellum might not always mean that the cerebellum is actively working on the task. It might light up simply because its connected neocortical areas are working. But does this mean that we had better abandon cerebellar imaging altogether? Are there tasks in which cerebellum specifically lights up, not reflecting activity in its connected neocortical regions?
In this thesis, we attempted to address these questions by reconsidering how we study cerebellar function using fMRI and see how it works in tandem with other brain regions, particularly the neocortex. To do this, we developed a tool to identify the neocortical regions that are sending input to the cerebellum. With this tool we can then investigate cerebellar activity in the context of its corresponding neocortical regions and ask which tasks engage the cerebellum specifically. We coined the term "selective recruitment" to discern when the cerebellum is uniquely involved.
Our results indicate distinct scenarios where the cerebellum takes the lead: like rapid alternating movements or encoding extensive information in memory. In essence, our work offers a fresh lens to understand the roles of this seemingly small brain structure.
Recommended Citation
Shahshahani, Ladan, "Selective recruitment of cerebellum in cognition" (2023). Electronic Thesis and Dissertation Repository. 9653.
https://ir.lib.uwo.ca/etd/9653
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License