Behavioural Brain Research 165 (2005) 229–239 Research report Mentally represented motor actions in normal aging I. Age effects on the temporal features of overt and covert execution of actions Xanthi Skoura a , Charalambos Papaxanthis b,∗ , Annie Vinter a , Thierry Pozzo b a Laboratoire d’Etude de l’apprentissage et du d´ eveloppement (LEAD), CNRS UMR 5022, Universit´ e de Bourgogne, Dijon, France b Motricit´ e et Plasticit´ e, INSERM/ERIT-M 0207, Universit´ e de Bourgogne, U.F.R.S.T.A.P.S., Campus Universitaire, B.P. 27877, 21078 Dijon, France Received 31 March 2005; received in revised form 3 July 2005; accepted 5 July 2005 Available online 13 September 2005 Abstract The present study examines the temporal features of overt and covert actions as a function of normal aging. In the first experiment, we tested three motor tasks (walking, sit–stand–sit, arm pointing) that did not imply any particular spatiotemporal constraints, and we compared the duration of their overt and covert execution in three different groups of age (mean ages: 22.5, 66.2 and 73.4 years). We found that the ability of generating motor images did not differentiate elderly subjects from young subjects. Precisely, regarding overt and covert durations, subjects presented similarities for the walking and pointing tasks and dissimilarities for the stand-sit-stand task. Furthermore, the timing variability of imagined movements was always greater compared to actual movements and was of the same amount in the three groups of age. In the second experiment, we investigated the effect of age (three groups with mean ages: 22, 64.8 and 73.2 years) upon temporal characteristics of covert and overt movements involving strong spatiotemporal constraints (speed/accuracy trade-off paradigm). During overt execution young and elderly subjects respected Fitts’s law despite the fact that movement speed progressively decreased with age. Thus, while execution is deteriorated, the motor preparation process is still intact in old age, and follows well-known laws of biological motions. For covert execution, movement speed progressively decreased with age but elderly subjects did not respect Fitts’s law. This suggests that the generation and control of motor intentions that consciously do not come to execution, particularly those concerning complex motor actions are progressively perturbed in the aging brain. © 2005 Elsevier B.V. All rights reserved. Keywords: Aging; Motor imagery; Motor prediction; Movement timing; Human; Locomotion; Sit–stand–sit; Arm movement 1. Introduction The ability of generating mental images allows humans to carry out cognitive operations on static and moving objects or individuals whilst they are absent from their sensory- perceptual system. This top-down process within the central nervous system (CNS) has a considerable biological signif- icance as it permits humans to recall past- and/or to predict and anticipate future-events and actions. Internal movement ∗ Corresponding author. Tel.: +33 3 80396748; fax: +33 3 80396702. E-mail address: charalambos.papaxanthis@u-bourgogne.fr (C. Papaxanthis). simulation, commonly termed as motor imagery, is a large part of this mental process and it can be defined as a mental state during which a subject replicates an action without any apparent motion of the limbs involved in the actual execu- tion of the same action. Covert movement execution can be operated on simple and complex movements involving either isolated limbs or the whole body in interaction with the envi- ronment (see, for instance, motor tasks performed by athletes or musicians). Several experimental investigations have been devoted to a description and an understanding of the similarities and dissimilarities existing at the neural and functional level, between executed and internally simulated motor actions. 0166-4328/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.bbr.2005.07.023