The effect of semantic memory degeneration on creative thinking: A voxel-based morphometry analysis.

Increasing attention is being directed towards explicating the neurocognitive mechanisms of divergent thinking. While neuroimaging studies have tended to dominate the contemporary creativity literature, lesion studies provide important converging evidence by revealing the regions that are not only implicated in, but essential for, task performance. Here we explored the capacity for divergent thinking in semantic dementia (SD), a neurodegenerative disorder characterised by the progressive degeneration of the conceptual knowledge base. The performance of 10 SD patients on a divergent thinking task was contrasted with that of 15 patients with the behavioural variant of frontotemporal dementia (bvFTD) and 20 healthy control participants. In addition, all participants underwent neuropsychological testing and structural MRI. Relative to controls, both patient groups generated significantly fewer responses on the divergent thinking task, with disproportionate impairment in the SD group. Further, the responses generated by patient groups were less original and reflected less flexible thinking when compared with controls. For SD patients, fluency of responses correlated with performance on a measure of semantic association, and originality of responses correlated with semantic naming and comprehension ability. In bvFTD, originality of ideas correlated with letter fluency and response inhibition. Voxel-based morphometry analyses revealed two grey matter clusters consistently associated with diminished Fluency of ideas, namely a left medial temporal lobe cluster centred on the left anterior hippocampus, and a left middle frontal gyrus cluster. Our study highlights the importance of distinct temporal and prefrontal contributions to divergent thinking via a lesion approach, and underscores the pivotal role of semantic processes in creative cognition.

Bedding down new words: Sleep promotes the emergence of lexical competition in visual word recognition.

Lexical competition processes are widely viewed as the hallmark of visual word recognition, but little is known about the factors that promote their emergence. This study examined for the first time whether sleep may play a role in inducing these effects. A group of 27 participants learned novel written words, such as banara, at 8 am and were tested on their learning at 8 pm the same day (AM group), while 29 participants learned the words at 8 pm and were tested at 8 am the following day (PM group). Both groups were retested after 24 hours. Using a semantic categorization task, we showed that lexical competition effects, as indexed by slowed responses to existing neighbor words such as banana, emerged 12 h later in the PM group who had slept after learning but not in the AM group. After 24 h the competition effects were evident in both groups. These findings have important implications for theories of orthographic learning and broader neurobiological models of memory consolidation.