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This PhD thesis investigated the role of the basal ganglia in memory and motor inhibition. Recent neuroimaging evidence suggests a supramodal network of inhibition involving the lateral prefrontal cortex. Here we examined whether this supramodal network also includes subcortical structures, such as the basal ganglia. Despite their well-established role in motor control, the basal ganglia are repeatedly activated but never interpreted during memory inhibition.
We first used a series of meta-analyses to confirm the consistent involvement of the basal ganglia across studies using memory and motor inhibition tasks (including the Go/No-Go, Think/No-Think, and Stop-signal tasks), and discovered that there may be different subprocesses of inhibition. For instance, while the Go/No-Go task may require preventing a response from taking place, the Think/No-Think and Stop-signal tasks may require cancelling an emerging or ongoing response.
We then conducted an fMRI study to examine how the basal ganglia interact with other putative supramodal regions (e.g., DLPFC) to achieve memory and motor inhibition during prevention and cancellation. Through dynamic causal modelling (DCM), we found that both DLPFC and basal ganglia play effective roles to achieve inhibition in the task-specific regions (hippocampus for memory inhibition; primary motor cortex (M1) for motor inhibition). Specifically, memory inhibition requires a DLPFC-basal ganglia-hippocampus pathway, whereas motor inhibition requires a basal ganglia-DLPFC-M1 pathway. We correlated DCM coupling parameters with behavioural indices to examine the relationship between network dynamics during prevention and cancellation and the successfulness of inhibition. However, due to constraints with DCM parameter estimates, caution is necessary when interpreting these results.
Finally, we used diffusion weighted imaging to explore the anatomical connections supporting functions and behaviour. Unfortunately, we were unable to detect any white matter variability in relation to effective connectivity or behaviour during the prevention or cancellation processes of memory and motor inhibition at this stage.
This PhD thesis provides essential INITIAL evidence that not only are the basal ganglia consistently involved in memory and motor inhibition, but these structures are effectively engaged in these tasks, achieving inhibition through task-specific pathways. We will discuss our findings, interpretations, and future directions in the relevant chapters. |
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