Inclusion Criteria for patients:  Diagnosis of bvFTD according to Rascovsky's international criteria for the bvFTD group / diagnosis of AD according to Dubois's international criteria for the AD group; No evidence of any other cerebral pathology; A Mini-Mental State Evaluation (MMSE) score superior or equal to 10 (to minimise the effect of confounding factors related to very severe cognitive impairment); Aged between 40 and 85; No evidence of any psychiatric condition and a Montgomery-Åsberg Depression Rating Scale (MADRS) score inferior to 20 (to avoid confusion between depression and apathy); No evidence of excessive consumption of psychotropic drugs - for instance benzodiazepines, sleeping pills, etc. (due to their tranquilising effect); No major physical disability disrupting mobility; No heart pacemaker (which would compromise heart rate measuring).  Inclusion Criteria for caregivers and partners of healthy control dyads:  Aged between 40 and 85; No evidence of any psychiatric condition; A MADRS score inferior to 20; No evidence of excessive consumption of psychotropic drugs; No major physical disability disrupting mobility; No heart pacemaker.  Exclusion Criteria:  Persons in detention by judicial or administrative decision Person who is subject to a legal protection order Person submitted to an exclusion period due to the participation to another research