Motor signatures of emotional reactivity in frontotemporal dementia.

Automatic motor mimicry is essential to the normal processing of perceived emotion, and disrupted automatic imitation might underpin socio-emotional deficits in neurodegenerative diseases, particularly the frontotemporal dementias. However, the pathophysiology of emotional reactivity in these diseases has not been elucidated. We studied facial electromyographic responses during emotion identification on viewing videos of dynamic facial expressions in 37 patients representing canonical frontotemporal dementia syndromes versus 21 healthy older individuals. Neuroanatomical associations of emotional expression identification accuracy and facial muscle reactivity were assessed using voxel-based morphometry. Controls showed characteristic profiles of automatic imitation, and this response predicted correct emotion identification. Automatic imitation was reduced in the behavioural and right temporal variant groups, while the normal coupling between imitation and correct identification was lost in the right temporal and semantic variant groups. Grey matter correlates of emotion identification and imitation were delineated within a distributed network including primary visual and motor, prefrontal, insular, anterior temporal and temporo-occipital junctional areas, with common involvement of supplementary motor cortex across syndromes. Impaired emotional mimesis may be a core mechanism of disordered emotional signal understanding and reactivity in frontotemporal dementia, with implications for the development of novel physiological biomarkers of socio-emotional dysfunction in these diseases.

Dissecting IWG-2 typical and atypical Alzheimer's disease: insights from cerebrospinal fluid analysis.

Pathobiological factors underlying phenotypic diversity in Alzheimer's disease (AD) are incompletely understood. We used an extended cerebrospinal fluid (CSF) panel to explore differences between "typical" with "atypical" AD and between amnestic, posterior cortical atrophy, logopenic aphasia and frontal variants. We included 97 subjects fulfilling International Working Group-2 research criteria for AD of whom 61 had "typical" AD and 36 "atypical" syndromes, and 30 controls. CSF biomarkers included total tau (T-tau), phosphorylated tau (P-tau), amyloid ß1-42, amyloid ßX-38/40/42, YKL-40, neurofilament light (NFL), and amyloid precursor proteins α and ß. The typical and atypical groups were matched for age, sex, severity and rate of cognitive decline and had similar biomarker profiles, with the exception of NFL which was higher in the atypical group (p = 0.03). Sub-classifying the atypical group into its constituent clinical syndromes, posterior cortical atrophy was associated with the lowest T-tau [604.4 (436.8-675.8) pg/mL], P-tau (79.8 ± 21.8 pg/L), T-tau/Aß1-42 ratio [2.3 (1.4-2.6)], AßX-40/X-42 ratio (22.1 ± 5.8) and rate of cognitive decline [1.9 (0.75-4.25) MMSE points/year]. Conversely, the frontal variant group had the highest levels of T-tau [1185.4 (591.7-1329.3) pg/mL], P-tau (116.4 ± 45.4 pg/L), T-tau/Aß1-42 ratio [5.2 (3.3-6.9)] and AßX-40/X-42 ratio (27.9 ± 7.5), and rate of cognitive decline. Whilst on a group level IWG-2 "typical" and "atypical" AD share similar CSF profiles, which are very different from controls, atypical AD is a heterogeneous entity with evidence for subtle differences in amyloid processing and neurodegeneration between different clinical syndromes. These findings also have practical implications for the interpretation of clinical CSF biomarker results.