| Summary: | This thesis will describe a set of experiments where the association between strategy use and the frontal lobes will be limited to the lateral prefrontal cortex. A particular, well-characterised strategy, that of chunking, will be centred on. In addition, the thesis will describe attempts at showing impairments on such tasks in patients. Initially a summary of the relevant literature and a description of general methods relating to the experiments of this thesis are given in chapters 1 and 2 respectively. Chapter 3 discusses a neuroimaging study using Positron Emission Tomography where a variant of a standard working memory task, that of spatial span, is given to subjects. While previous studies have shown an association between spatial span and the ventrolateral prefrontal cortex, this version is associated instead with the dorsolateral prefrontal cortex. In chapter 4, a follow-up Positron Emission Tomography study will be described, where two variants of the spatial span task are directly compared within subjects. The versions differ in the level of organisational structure of the spatial arrays. More activity in the dorsolateral prefrontal cortex is observed for the span task with the more structured array compared to a control than the span task with the less structured array. This experiment replicates the results of the previous chapter, while demonstrating that subtle differences in a working memory task can elicit associative changes within the lateral prefrontal cortex. Chapter 5 describes a behavioural study using similar spatial span tasks to the previous neuroimaging chapter, in order to explore possible behavioural differences that may correspond to the established differences in activation patterns of chapter 4. The results suggest that the crucial difference is that for the more orderly spatial array span task, there is a greater strategic component to the task. Chapter 6 outlines a study involving frontal lobe patients, where the spatial span versions of chapter 5 are presented to this patient group as well as closely matched controls. The results indicate that frontal lobe patients are impaired on such working memory tasks, contrary to the prevailing opinion about this patient group. In addition, there is a slight trend for the patients to be further impaired at the more structured version of the span, in line with the neuroimaging results of chapter 4.
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