Neural correlates of changes in sexual function in frontotemporal dementia: implications for reward and physiological functioning

Background Frontotemporal dementia (FTD) is characterised by changes in behaviour including alterations in sexual function. While hypersexual behaviour is commonly thought to predominate, emerging evidence suggests that hyposexual behaviour is in fact most prevalent. The underlying mechanisms driving these behavioural changes remain unclear; however, likely reflect interactions between cognitive, emotional, reward processing and physiological functioning. We aimed to systematically quantify changes in sexual behaviour in behavioural variant FTD (bvFTD) and semantic dementia (SD) in contrast with Alzheimer's disease (AD) and to elucidate the neural correlates of these changes using whole-brain voxel-based morphometry. Methods Carers of 62 dementia patients (30 bvFTD, 12 SD, 20 AD) were interviewed using the Sexual Behaviour and Intimacy Questionnaire, which assesses changes in sexual function. Voxel-based morphometry analysis of structural MRI brain scans was used to determine the association between changes in grey matter intensity and the presence of hyposexual, hypersexual, and inappropriate sexual behaviour across groups. Results Widespread attenuation of sexual drive, intimacy and the display of affection were evident irrespective of dementia subtype. In contrast, hypersexual and inappropriate sexual behaviour was present in only a small proportion of patients. Neuroimaging analyses revealed an association between hyposexual behaviour and atrophy of the right supramarginal gyrus, middle frontal gyrus and thalamus, whilst hypersexual behaviour was associated with cerebellar atrophy. Conclusion Counter to the prevailing view, younger-onset dementia syndromes predominantly display an attenuation in sexual drive. Changes in sexual function likely reflect the degeneration of cortical and subcortical neural circuits implicated in reward, autonomic function, empathy, and emotional processing.