Research report Does order and timing in performance of imagined and actual movements affect the motor imagery process? The duration of walking and writing task Charalambos Papaxanthis a, *, Thierry Pozzo a , Xanthi Skoura b , Marco Schieppati c a Laboratoire Motricite ´ et Plasticite ´ (LMP), Universite ´ de Bourgogne, Dijon, France b Laboratoire d’Etude de l’apprentissage et du de ´ veloppement (LEAD), Universite ´ de Bourgogne, Dijon, France c Human Movement Laboratory (CSAM), ‘Salvatore Maugeri Foundation’ (IRCCS), Scientific Institute of Pavia, and Institute of Human Physiology, University of Pavia, Pavia, Italy Received 16 October 2001; received in revised form 23 January 2002; accepted 23 January 2002 Abstract The purpose of the present study was to investigate the effects on the duration of imagined movements of changes in timing and order of performance of actual and imagined movement. Two groups of subjects had to actually execute and imagine a walking and a writing task. The first group first executed 10 trials of the actual movements (block A) and then imagined the same movements at different intervals: immediately after actual movements (block I-1) and after 25 min (I-2), 50 min (I-3) and 75 min (I-4) interval. The second group first imagined and then actually executed the tasks. The duration of actual and imagined movements, recorded by means of an electronic stopwatch operated by the subjects, was analysed. The duration of imagined movements was very similar to those of actual movements, for both tasks, regardless of either the interval elapsed from the actual movements (first group) or the order of performance (second group). However, the variability of imagined movement duration was significantly increased compared to variability of the actual movements, for both motor tasks and groups. The findings giveevidence of similar cognitive processes underlying both imagination and actual performance of movement. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Motor imagery; Mental chronometry; Working memory; Walking; Writing; Forward models; Human 1. Introduction The motor imagery process involves brain regions essential to the performance of motor actions [1 / 3,10,13,14,17,18,28,30]. A number of experiments has argued for a functional relationship between motor imagery and actual movement execution, thus further strengthening the similarities between these two types of movement execution [12,19  /21]. For instance, it has been shown that muscular force is enhanced by an ‘imagined’ training [34] and that autonomic activation is increased, compared to rest, when subjects imagine motor actions with large physical effort [7,8,26]. In addition, psychophysical experiments showed that ima- gined movements preserve the same spatio-temporal characteristics and obey the same laws of movement control as those of actual movements [4  /6,9,30]. This anatomical and functional correspondence between motor imagery and actual movement execution is very attractive, and suggests that the motor preparation and the programming process are almost identical when subjects execute or imagine an action. However, to our knowledge, all mental behaviour protocols have always addressed the issue of spatio- temporal similarities between imagined and actually executed actions, under conditions in which the trials of imagined movements either closely followed a session of actual movements or were randomised with actual movements, thereby possibly producing a mutual influ- ence between the two types of movement. In other words, the theoretical justification of randomisation, to avoid a bias connected to the structure of an ordered * Corresponding author. Present address: UFR STAPS, Universite ´ de Bourgogne, Campus Universitaire, BP 27877, Dijon 21078, France. Tel.: 33-3-80396748; fax: 33-3-80396702 E-mail address: charalambos.papaxanthis@u-bourgogne.fr (C. Papaxanthis). Behavioural Brain Research 134 (2002) 209 /215 www.elsevier.com/locate/bbr 0166-4328/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0166-4328(02)00030-X