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.

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.

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.

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.

the reaction time task may be a promising tool for an objective evaluation of the initiative and interest dimensions of apathy in neurodegenerative diseases.