Recognition memory impairments in temporal lobe epilepsy: The contribution of recollection and metacognition

Temporal lobe epilepsy (TLE) is a complex neurological condition associated with a variety of memory problems. This thesis attempted to elucidate the nature and extent of memory impairments further in this clinical group by drawing on dual-process theory of memory (Tulving, 1985; Jacoby, 1991; Yonelinas, 1994). This theory asserts that memory is subserved by two interrelated but independent memory processes. Recollection involves the vivid retrieval of contextual and associative information from memory. Conversely, familiarity involves recognition in the absence of this contextual information. The novel approach taken in this work was to compare paradigms that assess participants’ objective and strategic use of these two processes with measures of people’s subjective experience of their memory.

Chapter 2 set the scene by presenting the extent of objective memory impairment in the current patient sample by means of standardised neuropsychological testing. Chapter 3 – 5 assessed subjective and objective recollection in anterograde recognition memory tasks. Chapter 3 showed that patients’ subjective experience of remembering may be driven by qualitatively different types of information to healthy adults. Chapter 4 demonstrated that patients were impaired in their strategic use of recollection and concurrently showed reduced levels of subjective remembering. This demonstrated that patients can be consciously aware of deficits in underlying cognitive processes contributing to memory performance. Chapter 5 specifically examined a metacognitive account of this recollection deficit. Patients were found to have impairments in a number of measures that index relational binding ability. However, their subjective confidence was assigned appropriately; they were lesser confident in their recognition judgments overall and adjusted this confidence in line with the difficulty of materials and task demands comparably to controls. Chapter 6 took a more naturalistic approach and assessed self-reported memory complaint as well as retrograde memory for salient public news events. As expected, people with TLE subjectively complained of dissatisfaction with their day-to-day to memory. The public events task revealed that although patients had reductions in subjective measures associated with recollecting the events, they were just as able as controls to accurately date the news items and monitor their memory for these. Chapter 7 found correlations between a variety of the subjective and objective recollection scores derived in the various tasks.

This thesis provides confirmatory evidence that memory impairment in TLE is characterised by disordered recollection and recollective experience. Several important theoretical and clinical applications of these findings are discussed.