Taste- and odor-reactivity in elderly demented patients

Previous studies demonstrated that hedonically different chemical (taste or smell) stimuli induceinnate, inherited, differential and distinct fixed reflectory motion features in the oral and facial area. In the present study 20 elderly demented patients, suffering from ‘probable’ or ‘possible’ Alzheimer's disease, and 20 normally functioning elderly subjects were tested. The facial expressive behavioral reactions triggered by a set of common gustatory and olfactory stimuli were videotaped. Both psychophysical and stimulus-dependent behavioral responses were obtained from the control group, while for the demented patients only behavioral reactions were recorded. Results revealed that: (i) severely demented elderly subjects displayed differential and distinct orofacial responses indicating ‘acceptance’ and ‘aversion’. These were found to be analogous to but less intense than those displayed by control age mates; (ii) the duration of responses induced by aversive tastes is longer than that triggered by pleasant or indifferent ones, for both groups; (iii) all gustatory and olfactory stimuli trigger a longer lasting behavioral response in demented than in normal subjects; and (iv) psychophysical and behavioral responses of the control subjects gave similar results for taste- and odor-hedonics as well as for their intensity. This finding clearly indicates the validity of the alternative use of psychophysical and behavioral testing procedures.