Experience-dependent modulation of collective behavior in larval zebrafish.

Recent years have seen increased attention on a form of frontotemporal dementia (FTD) associated with atrophy predominantly affecting the right-anterior temporal lobe (R-ATL). Impaired recognition of people, compulsions/preoccupations, and loss of empathy have been identified as core characteristics [–], and a multi-centre international cohort study of 360 patients [] demonstrated, in addition, high frequencies of apathy, behavioural disinhibition, naming difficulty, and memory impairment. Studies of FTD with R-ATL predominance are immensely valuable. First, they draw attention to a presentation of FTD that may be under-recognised. Second, they potentially improve understanding of the role of the right temporal lobe in cognition and behaviour. They also pose a fundamental question of nosology. How should diverse clinical presentations be accounted for within clinical diagnostic frameworks for FTD? It has been argued that R-ATL predominant FTD should be considered a distinct clinical entity, separate from its left-temporal lobe (L-ATL) counterpart, semantic variant primary progressive aphasia (svPPA). The designation “semantic behavioural variant FTD” has been proposed to capture the mixed picture of behavioural and semantic symptoms []. The term ‘semantic dementia’ (SD) has, however, long been used to encompass patients with both left and right-predominant ATL atrophy [–], and behavioural change has been acknowledged as an integral component of the syndrome [, ]. An implicit assumption in using this term is that left- and right-predominant ATL are variants of the same underlying clinicopathological entity. An important consideration in addressing the relationship between R and L-ATL is the extent to which features that characterise R-ATL FTD are shared by patients with L-ATL predominance. Patients with R-ATL predominance are, thus far, identified purely on radiological grounds. It is essential that comparisons should involve L-ATL predominant patients also selected on radiological grounds rather than a specific FTD subvariant, e.g., svPPA. The present study aimed to provide such a comparison. It comprised a retrospective examination of information recorded in case notes of patients attending a specialist diagnostic clinic for early onset and rare dementias. It was enabled by the fact that clinic assessments involve a structured clinical history of cognitive and behavioural changes and neuropsychological assessment, so that comparable information is available for all patients, recorded independently and without prior knowledge of neuroradiological findings.