Background:Apathy, defined as a lack of motivation, is common in neurodegenerative diseases. Specific scales are available for the evaluation of apathy but it lacks objective evaluation methods.Aim:To evaluate the changes in reaction time task according to the presence or absence of reward stimulation and to assess the relation between these performances and apathy scales.Methods:13 patients with Mild Cognitive Impairment, 15 patients with Alzheimer's disease and 91 elderly healthy subjects were enrolled. A computerized test using the experiment software E-prime® was designed to assess reaction times in different experimental conditions after a training trial (neutral, stimulation, stress, stimulation after stress, extinction) and relation between the performances to the test and the Apathy Inventory (AI) scores were observed.Results:Patients reaction times were significantly higher than control. Reactions times were lower in stimulation conditions and maximum during the stress condition. In the patients population, apathetic subjects (AI total score >2) had significantly higher reaction times than non apathetic subjects (p<0,05). We found significant positive correlation between AI dimensions lack of initiative and lack of interest, and reaction times in the following conditions: lack of interest and neutral condition (p<0,01), stimulation condition (p<0,05), lack of initiative and stress condition (p<0,05). Furthermore, AI total score was correlated with both stimulation and extinction conditions (p<0,05). There was no significant correlation with the emotional blunting.Conclusion:the reaction time task may be a promising tool for an objective evaluation of the initiative and interest dimensions of apathy in neurodegenerative diseases.