Background Behavioural variant Frontotemporal dementia (bv-FTD) causes disabling behaviour and personality changes. A systems level understanding of neurocognitive dysfunction remains underdeveloped, relative to the molecular biology and neuropsychological. We examined responses to unexpected sounds (Mismatch negativity, MMNm) using Magnetoencephalography (MEG). The MMN exemplifies a fundamental generalised predictive coding model of sensory, motor and cognitive phenomena (Garrido et al, 2009).
Methods We used the Optimum paradigm (Naatanen et al, 2004) with deviant and standard tones in 11 patients and 18 controls. 1800 tones were presented every 500 ms. MEG used BESA. 2-source and 6-source ECD models examined MMNm sources and coherence between temporal, frontal and parietal cortex in alpha, beta, and 3γ bands.
Results FTD reduced the MMNm response with no differences in latency. Coherence analysis confirmed reduced left frontotemporal coherence especially in the alpha and beta bands. Frontal inter-hemispheric gamma coherence was reduced, but temporal and parietal inter-hemispheric gamma coherence was increased.
Conclusion bv-FTD reduced auditory MMN response with abnormal cortico-cortical coherence, despite normal responses to standard tones. The shift from frontal to parietal gamma coherence may reflect compensatory reorganisation of neural networks in regions of cortex that are less severely affected by neurodegeneration.