van Essen et al. Mefloquine induced motor deficits Figure 4 | eye-blink conditioning is impaired by the intake of mefloquine. (A) Left panel: Schematic drawing of eye-blink conditioning. Right panel: eyelid movement recording of a response before (UR: unconditioned response) and after conditioning (CR: conditioned response). (B) Example of 48 eyelid recordings of a control subject (i.e., no mefloquine use; left panel) and a mefloquine user (right panel) during the acquisition.The conditioned stimulus (CS) is indicated by the light-blue bar, ranging from 500 to 1020 ms.The unconditioned stimulus (US) is indicated by the vertical black line, ranging from 1000 to 1020 ms. (C) Histogram of the total number of CRs in % observed in control subject (blue, n = 11) and mefloquine users (red, n = 8; *p < 0.05, t test). (D)The average percentages of CRs in each acquisition block is plotted for the control group (blue squares) and mefloquine group (red squares). Learning curves were used to fit both data sets (Rc2ontrol = 0.98 and Rm2efloquine = 0.87). within the blocks and as a whole. The eight blocks were preceded by the first block, called block 0, during which participants were presented tone-only trials. In this block, we confirmed that the participants did not yet learned the ability to make a conditioned eye-blink response. ItatsIlacesylna With regard to the performance experiments, all comparisons were done with paired, two-tailed t test. For the learning experiments (i.e., eye-blink conditioning), we used the unpaired, two-tailed t test. Furthermore, we fitted this learning data set with the following learning curve: the exponential function y = a − a. exp−x/b, where y is the percentage of CRs, x the block number, and a and b are the learning coefficients (a represents learning capacity and b learning speed) of the model. The goodness of fit was indicated by R2 values. All mean values were accompanied by standard error of the mean (SEM) unless stated otherwise. stluser In the study period of July 2009 to April 2010, 28 individuals were included. Nine participants volunteered for the perform- ance experiments and 19 for the motor learning experiments (8 used mefloquine; 11 individuals served as control participants [no mefloquine use]). Table 1 summarizes the general characteristics of the individuals participating in the performance and motor learn- ing experiments. Six participants reported adverse events after the intake of mefloquine (see Table 1). Pcnamofreyratnulovm t Im I,gn Pcre Plaut t Im I,gn dna xlfer ItImgn Is tondtcefa In Iuqolfemen resu To find out whether mefloquine leads in humans to deficits in olivocerebellar related performances, we tested our partici- pants before and after the intake of mefloquine (i.e., off and on medication), using specific tasks in which the IO is thought to be involved. Voluntary motor timing was assessed by a dart throwing task. Throwing imprecision can be divided in a vertical and horizontal component. Imprecision in release timing or throwing speed is more reflected in the vertical deviation than in the horizontal deviation to the target (Figure 1A). Our participants revealed a significant larger vertical deviation than horizontal deviation under both conditions (Figure 1C, meflo: p = 0.01, no meflo: p = 0.01, t test), indicating the more complex control of the vertical component over the hori- zontal component of the throw. The vertical deviation as well as the horizontal deviation was not affected by the use of mefloquine (Figure 1C, p = 0. 47 and p = 0.73 respectively, n = 9, t test). In order to correct for non-specific inter-trial variability, we normalized the vertical deviation by the total deviation of each throw. These nor- malized vertical deviations did not reveal a significant difference (Figure 1D, p = 0.45, n = 9, t test). Neither did the normalized variation in the vertical deviation, which is an indicator for vertical throwing precision (Figure 1E, p = 0.34, n = 9, t test). Since the IO has been suggested to play a role in the perception of complex rhythms (Xu et al., 2006), we investigated whether a rhythm perception task in mefloquine users would result in reduced ability to distinguish between rhythms (Figure 2A). No significant differences were found with respect to the number of errors made per perturbation between the two conditions (Figure 2B). The 25 ms perturbation yielded the largest difference, although not significant (p = 0.25, n = 9, t test). The effect of mefloquine on an involuntary motor performance task was investigated by studying the reflex blink (Figure 3A). Reflex blinks obtained before and after the intake of mefloquine were ana- lyzed kinetically. The onset, the peak time velocity and the peak time amplitude did not reveal a significant difference between partici- pants “off ” mefloquine compared to “on” mefloquine (Figure 3B, p = 0.78, n = 9, t test). The precision in timing of the eye-blink was investigated by testing the standard deviation of these parameters. Although, the standard deviations were all larger when the par- ticipants were under the influence of mefloquine, they were not significantly larger (Figure 3C, p = 0.59, n = 9, t test). www.frontiersin.org November 2010 | Volume 4 | Article 191 | 5