One trial was achieved when the monkey opened the find more drawer with one hand, kept it open, and grasped the pellet with the other hand (see http://www.unifr.ch/neuro/rouiller/research/PM/pm1.html [video sequence 10]). Handedness questionnaire At the end of the manual dexterity tasks, the human subjects were asked to answer a handedness questionnaire, elaborated by

MacManus (2009). Inhibitors,research,lifescience,medical It was chosen because it fills several pertinent criteria to assess handedness in human subjects (Oldfield 1971). The questions dealt with actions of daily life such as: with which hand do you write, do you hold a potato while you are peeling it, do you throw a ball, etc. Analysis of data The data of the behavioral tasks were analyzed manually from the recorded video sequences. The software VirtualDubMpeg2® (Developper Avery Lee, free software, http://www.virtualdub.org) allowed visualizing the video sequences frame by frame, corresponding to a time resolution of 40 msec (acquisition Inhibitors,research,lifescience,medical Inhibitors,research,lifescience,medical at 25 frames per second). The data were processed first in Excel® worksheets, before they were transferred to Sigmastat®/Sigmaplot® (Systat Software Inc., http://www.sigmaplot.com) and SPSS® (SPSS Inc., Chicago, IL) allowing more elaborated

graphic representation and statistical analysis. The hand dominance was determined based on a single task, the modified Brinkman board task performed with one hand imposed at a time. Two types of data were analyzed for the monkeys (Schmidlin

et al. 2011). (i) The score, defined as the number of pellets correctly retrieved during the first 30 sec; (ii) The contact time (CT), defined Inhibitors,research,lifescience,medical as the time interval between the first contact of a finger Inhibitors,research,lifescience,medical (most often the index finger) with the pellet and the moment when the fingers left the slot with the reward. The CT is a pertinent parameter in addition to the score, as the latter can sometimes be biased. Indeed, the animal may be disturbed by external noises, or may exhibit a lack of motivation or concentration. In such cases, the monkey may interrupt the test, leading to a distortion of the score. Moreover, the CT truly measures the actual manipulation of the pellets with unless the fingers. The CT was measured for the first five horizontal and the first five vertical slots in the 20 last daily sessions at plateau, whereas the score was calculated for every daily session. The onset of the plateau was defined, when the learning curve tended to saturate (as estimated by visual inspection), as the first value in the nearly flat curve of the score that was not exceeded by one of the five following score values. For human subjects, the analysis of hand dominance was based mainly on the score in 30 sec, although the CT was also established for comparison in a sample of subjects.