UBC Theses and Dissertations
Coding of sequential behaviors by anterior cingulate cortex ensembles Ma, Liya
The anterior cingulate cortex (ACC) has been implicated in a myriad of different functions. Converging evidence suggests that the ACC continuously monitors and evaluates actions and their consequences. Such functions are essential in representing action sequences which are the building blocks of all complex behaviors. This dissertation seeks to delineate how ACC neuronal ensembles represent different types of information with special emphasis on action sequences. Chapter 2 shows that the ACC ensembles represents different action sequences via unique activity patterns that change if the order of the actions are altered or if the locations of the actions is changed. Interestingly such shifts are achieved when overall levels of activity remain fixed. Chapter 3 reveals a very different arrangement in which progression through a sequence of actions towards a goal is associated with a change in the overall level of neural activity without a significant change in the patterns of activity. Specifically, ACC ensembles display a smooth progressive change in overall activity over three lever press actions that culminate in a reward. In contrast, the dorsal striatal (DS) ensembles recorded simultaneously from the same animals display fluctuations in activity level that are tightly linked to each action. Together these two chapters show that the ACC may use two different firing rate-related codes to convey categorical versus continuous forms of information. Chapter 4 provides a further examination of the mechanisms which allows the ACC ensembles to encode multiple types of categorical information. While the DS neurons encode both the sequence and the location of the levers in a somewhat synchronized fashion, ACC neurons encoded both of these types of information but kept them functionally segregated. As a result, even though ACC single neurons were no better than the DS in sequence decoding, sequence decoding by ACC ensembles was far superior to DS ensembles. The last chapter attempts to produce a unified theory of ACC function based on its coding properties. I will argue that the ACC monitors many aspects of experience while evaluating the current state with reference to a goal. Its multiple coding schemes efficiently serve both monitoring and evaluating functions.
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