Introduction: The ageing of the population has generated an increase in chronic diseases and comorbidities, with Alzheimer's disease (AD) being frequent. The aim of three communications is to deepen our knowledge of cognitive impairment in dementias. A fourth communication studies the effects of direct transcranial electrical stimulation (dTES) in people with aphasia. Methods: Medical records were collected, screening tests and scales were administered, followed by the MetAphAs test or the Verbal-Executive Protocol. In two communications, the results obtained by a control group (healthy older adults (N =25 and 30, respectively)) were compared with the experimental group (Alzheimer=22; MCI=31)). The MetAphAs test was administered to a sample of 40 persons (AD=20; Logopenic aphasia=20). The EETd was administered to 13 people with aphasia, in a 4-week crossover (active-placebo) clinical trial with a 2-week "washout" period. Results: Significant group differences were observed in the MetAphAs test and the Verbal-Executive Protocol. Significant differences were found between pre- and post-test sessions, in the sessions with active EETd, not observed in the placebo condition. Conclusions: The Verbal-Executive Protocol is shown to be a useful tool for discriminating between healthy older adults and people with Alzheimer's or MCI. The MetAphAs test allows differentiating metalinguistic profiles in people with AD and logopenic aphasia. TEEd may be an effective technique in the treatment of patients with post-stroke aphasia with mild-moderate severity. Further studies are needed to obtain more consistent results.