Degradation of cognitive timing mechanisms in behavioural variant frontotemporal dementia

Abstract

The current study examined motor timing in frontotemporal dementia (FTD), which manifests as progressive deterioration in social, behavioural and cognitive functions. Twenty-patients fulfilling consensus clinical criteria for behavioural variant FTD (bvFTD), 11 patients fulfilling consensus clinical criteria for semantic-variant primary progressive aphasia (svPPA), four patients fulfilling criteria for nonfluent/agrammatic primary progressive aphasia (naPPA), eight patients fulfilling criteria for Alzheimer׳s disease (AD), and 31 controls were assessed on both an externally- and self-paced finger-tapping task requiring maintenance of a regular, 1500 ms beat over 50 taps. Grey and white matter correlates of deficits in motor timing were examined using voxel-based morphometry (VBM) and diffusion tensor imaging (DTI). bvFTD patients exhibited significant deficits in aspects of both externally- and self-paced tapping. Increased mean inter-response interval (faster than target tap time) in the self-paced task was associated with reduced grey matter volume in the cerebellum bilaterally, right middle temporal gyrus, and with increased axial diffusivity in the right superior longitudinal fasciculus, regions and tracts which have been suggested to be involved in a subcortical-cortical network of structures underlying timing abilities. This suggests that such structures can be affected in bvFTD, and that impaired motor timing may underlie some characteristics of the bvFTD phenotype.

Keywords: Cerebellum; Finger tapping; Frontotemporal dementia; Motor timing.

Fig. 1

Plots of externally-paced (left panels) and self-paced (right panels) unadjusted interresponse interval for both tapping tasks, each row showing controls, bvFTD, svPPA, naPPA and AD respectively.

Fig. 2

Regions in the bilateral cerebellum in which faster mean IRI in the self-paced tapping task was associated with reduced grey matter volume, p<0.05 (FWE correction across the whole brain). Findings are overlaid on an average image in MNI space, with coordinates in mm. The colour bar represents the corrected p value.

Fig. 3

Regions in the right superior longitudinal fasciculus in which faster mean IRI in the self-paced tapping task was associated with higher axial diffusivity, after FWE correction at p<0.05 in the white matter tracts of interest. The tracts investigated are shown in green, and significant findings overlaid in red, on a standard 1mm voxel MNI152 brain template from FSL, with coordinates in mm.