Abstract
OBJECTIVESemantic dementia, a subtype of frontotemporal lobar degeneration, is characterised by cross-modal loss of conceptual knowledge attributable to progressive degeneration of the left anterior temporal lobe. Much less is known regarding the clinical presentation of SD patients with predominantly right-lateralised atrophy. Recent reports emphasise marked socioemotional and behavioural disturbances in such cases. Given the importance of the right anterior temporal lobes in social cognition, we hypothesised that socioemotional functioning would be disproportionately affected in right versus left-lateralised SD cases.METHODSWe assessed well-characterised cases of predominantly right (n=10) and left (n=12) SD and 20 matched healthy controls on tests of emotion processing and interpersonal functioning.RESULTSRight SD cases showed disproportionate difficulties in the recognition of positive and negative facial emotions, specifically happiness and anger, compared with left SD cases. Deficits in anger recognition persisted in right SD despite covarying for facial and semantic processing. On a contextually rich task of emotion recognition using multimodal videos, no subgroup differences were evident. Finally, empathic concern was rated as significantly lower by caregivers of right versus left SD cases. Overall, the extent of socioemotional disturbance was associated with the degree of behavioural changes in SD.CONCLUSIONOur results reveal considerable overlap in the extent to which socioemotional processes are disrupted in left and right-lateralised cases of SD. Notably, however, right SD cases show disproportionate deficits for recognition of facial emotions and the capacity for empathic concern, supporting a specialised role for the right anterior temporal lobes in mediating these cognitive functions.
Highlights
Semantic dementia (SD) is a clinical syndrome associated with focal degeneration of the anterior temporal lobes of the brain, manifesting in the progressive cross modal deterioration of general conceptual knowledge.[1,2] Patients with SD present with severe semantic impairments due to asymmetrical, primarily left-sided, brain atrophy including the anterior and medial portions of the temporal lobe.[3,4] Extensive clinical and anatomical characterisations of predominantly left-sided SD cases concord with the lateralisation of verbal skills and phonological representations to the left hemisphere[5] and have proved illuminating for our understanding of the complex cognitive architecture of the semantic and episodic memory systems of the brain.[6]
No significant differences were evident between the left and right SD cases for disease duration (i.e. the time elapsed between symptom onset and testing, F(1, 20)=1.521, p=0.232) or disease severity (CDR Sum of Boxes, F(1, 16)=0.049, p=0.828; Addenbrooke’s Cognitive Examination-Revised (ACE-R) total score, F(1, 20)=0.181, p=0.675)
Striking semantic processing deficits were evident on the Naming (F(2, 38)=240.86, p
Summary
Semantic dementia (SD) is a clinical syndrome associated with focal degeneration of the anterior temporal lobes of the brain, manifesting in the progressive cross modal deterioration of general conceptual knowledge.[1,2] Patients with SD present with severe semantic impairments due to asymmetrical, primarily left-sided, brain atrophy including the anterior and medial portions of the temporal lobe.[3,4] Extensive clinical and anatomical characterisations of predominantly left-sided SD cases concord with the lateralisation of verbal skills and phonological representations to the left hemisphere[5] and have proved illuminating for our understanding of the complex cognitive architecture of the semantic and episodic memory systems of the brain.[6]. With alterations in dressing, personal hygiene, sociopathic behaviours, irritability, and impulsivity, appear more frequent in patients with predominantly right sided pathology in comparison with left-sided SD cases.[7] Together with loss of empathy and insight, disinhibition, and difficulties in affect regulation, such alterations in social comportment may bias the clinician to misdiagnose right SD as behavioural variant frontotemporal dementia, when structural neuroimaging is not available.[10]
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