Turner, Martha; (2005) Confabulation and memory impairments following frontal lobe lesions. Doctoral thesis , UCL (University College London).

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Abstract

Neuroimaging studies have provided considerable evidence for frontal lobe involvement in memory processing. Memory impairments arc also frequently reported in patients with frontal lobe lesions. However detailed anatomical localisation is rare, making integration of lesion and imaging findings difficult. An investigation of the functional and anatomical contributions of the frontal lobes to memory was conducted in 42 patients with frontal lobe lesions, examining memory processes identified in previous imaging and neuropsychological research. The results revealed frontal impairments in recall and recognition memory, increased false recognition and intrusions, and confabulation. To investigate specific lesion-behaviour relationships, patients were grouped according to the presence of damage in Right Lateral, Left Lateral, Medial and Orbital frontal regions. The Medial group had impairments in recognition and recall on several tasks, which were due at least in part to deficits at encoding. This group may have a pure memory deficit arising from disruption of cholinergic projections from the basal forebrain to the medial temporal lobe system. The Right Lateral group on the other hand had a strategic retrieval deficit which was aided by cueing at recall. Marked intrusion and confabulation effects were found in the Orbital and Medial groups, providing strong support for an inferior medial localisation for confabulation. In addition an investigation of Schnider and colleagues' theory of confabulation was conducted in three confabulating patients. Strong support was found for a characteristic pattern of performance on their continuous recognition task, with confabulators showing a constant hit rate accompanied by an increasing false positive rate. However the suggestion that the critical impairment is an inability to suppress currently irrelevant memories that intrude into the present was not supported. Instead these patients had a complete inability to place remembered information in its correct temporal context. There was also evidence of a tendency to misidentify imagined experiences as real. It is argued that retrieval process theories incorporating these factors are best able to account for the features of confabulation.

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