- Email: [email protected]
Modulation of anticipatory postural adjustments in a reactive and a self-triggered mode in humans
Neuroscience Letters 260 (1999) 109–112
Modulation of anticipatory postural adjustments in a reactive and a self-triggered mode in humans Vincent Nougier a ,*, Normand Teasdale b, Chantal Bard b, Michelle Fleury b a
Laboratoire Sport et Performance Motrice, Universite´ Joseph Fourier-Grenoble 1, BP 53, 38041 Grenoble cedex 9, France b Laboratoire de Performance Motrice Humaine, Universite´ Laval, Que´bec, Canada Received 21 October 1998; received in revised form 26 November 1998; accepted 26 November 1998
Abstract Five subjects raised their preferred arm until horizontal in one of two experimental conditions: (1) in response to a visual signal (reactive condition), and (2) in a self-triggered condition. In both conditions, subjects were instructed to execute the movement at approximately 80% of their maximal velocity, such that all movements were nearly similar. EMG activity was recorded in a focal muscle (Anterior Deltoidus) and in three postural muscles (ipsi-lateral Gastrocnemius, contra-lateral Tensor Fascia Latae and ipsi lateral Semitendinosus) known to be activated prior to the focal muscle. Results showed greater anticipatory postural adjustments in the self-triggered than in the reactive condition for the three postural muscles. It is suggested that similar intentional movements can be triggered by different timing strategies. 1999 Elsevier Science Ireland Ltd. All rights reserved.
Keywords: Anticipatory postural adjustments; Information processing; Human
It is now well established that posture and movement are highly integrated and require a good synchronization of both mechanisms [9]. More precisely, anticipatory postural adjustments (APAs) are generally observed when a movement has to be performed, as for example when raising a limb [4] or when voluntary unloading the forearm in a bimanual load lifting task [8,12]. In these intentional tasks, the muscles involved in the control of posture are activated prior to the muscles directly involved in the limb movement. The APAs allow to produce a shift of the center of gravity in the direction opposite to that of the focal movement, in order to compensate for the expected desequilibrium [4]. Intentional movements, however, can be performed in two conditions, at least: a reactive condition in response to an external signal and a self-triggered condition in which movement initiation is self-determined [2,10]. Previous studies investigated the onset of the APAs in a reaction time versus a self-paced condition of movement execution [3,5,7]. The results of these experiment were rather contradictory regarding the relative timing of the * Corresponding author. Tel.: +33 4 76514195; fax: +33 4 76514469; e-mail: [email protected]
0304-3940/99/$ - see front matter PI I : S0304- 3940(98) 00961- 6
APAs and the focal movement in the two conditions. One main reason was probably that the execution of the focal movement was not similar across the conditions and from one experiment to another. The purpose of the present experiment was to investigate the coordination of posture and movement in a reactive and self-triggered condition of movement initiation. To better isolate the effect of condition of movement initiation, a particular attention was devoted to a similar execution of the focal movement. Shorter APAs were expected in the reactive than in the self-triggered condition. As a result, a greater postural stability was also expected in the self-triggered than in the reactive condition. Five subjects (three right-handed and two left-handed), aged 26–37 years (mean age 32 years) participated in the experiment on a voluntary basis. Subjects stood feet together on a force platform. (KISTLER model 9284) which allowed measuring the displacement of the center of foot pressure. All signals were sampled at 50 Hz and then filtered with a second-order Butterworth filter (10 Hz lowpass cut-off frequency with dual pass to remove phase shift). Four prespaced (2.5 cm) Ag-AgCl surface electrodes were fixed to the central portion of respectively the Anterior Deltoı¨dus of the preferred hand, the ipsi-lateral Gastrocne-
1999 Elsevier Science Ireland Ltd. All rights reserved.
110
V. Nougier et al. / Neuroscience Letters 260 (1999) 109–112
mius, the contralateral Tensor Fascia Latae and the ipsi lateral Semitendinosus. The Anterior Deltoı¨dus was the main focal muscle of the movement (raising the arm). The other three muscles were considered as postural muscles. In a similar task, they were activated prior to the focal muscle, demonstrating the existence of APAs [4]. The electromyographic (EMG) signal was preamplified at the source (35 × ), filtered with a time constant of 2.5 ms, and bandpassed between 20 Hz and 4 kHz. In addition, an accelerometer was fixed on the external face of the hand. Force signals and accelerometer signal were collected at 500 Hz (12 bit A/D converter). The accelerometer was connected to an oscilloscope, such that the acceleration-time traces were stored and compared from trial to trial. When the trace deviated from the reference acceleration signal, the trial was rejected. Once having stabilized their posture on the force platform, subjects raised their preferred arm until horizontal, holding a 500 g weight in the hand. The arm raising was executed at a constant speed from trial to trial in two experimental conditions. In the reactive condition, subjects performed the movement in response to a visual signal (red light emitting diode). The onset of the response signal occurred randomly within 4 s, once subjects declared to be ready. It remained on until movement completion. In the self-triggered condition, subjects executed the movement whenever they were ready, within a 4 s period. In both conditions, subjects were instructed to execute the movement approximately at 80% of their maximal velocity, such that all movements were very similar. The acceleration-time traces served to control the similarity of the movements both in amplitude and time. These acceleration-time traces were compared from trial to trial via an oscilloscope. All trials which did not reach the criteria were immediately rejected (10% of the trials approximately). Subjects performed 20 correct trials for each condition. For all subjects, the reactive condition was presented first. The main dependent measure was the delay between EMG onset of the focal muscle and EMG onset of the three postural muscles. Delay was negatively signed when activation of the postural muscle preceded activation of the focal muscle, that is when an APA occurred. Fig. 1 illustrates, for a typical subject, the superimposition of five acceleration-time traces and the corresponding EMG signals for the two conditions. For illustration purposes, all signals are synchronized on the EMG onset of the focal muscle (Anterior Deltoı¨dus). A two-conditions × threemuscle analysis of variance with repeated measures on both factors was applied to the data. The results showed main effects of condition (F(1,4) = 7.82, P , 0.05) and muscle (F(2,8) = 16.51, P , 0.001). Postural muscles were activated earlier for the self-triggered than for the reactive condition. Furthermore, the APA was different according to the postural muscle involved. It was longer for the Semitendinosus than for the Tensor Fascia Latae which in turn was longer than for the Gastrocnemius.
Results also showed a significant interaction of condition × muscle (F(2,8) = 4.66, P , 0.05). As illustrated in Fig. 2, the increased APA as a function of the postural muscle activated was more important in the self-triggered than in the reactive condition. Since the subjects’ task was to raise the arm, the main COP displacements were observed mainly in the anteroposterior plane. Three different measures of postural stability were analyzed. The range indicates the maximal excursion of the COP from its original baseline. The displacement is the cumulated distance over the sampling period, that is, the overall sequence of movement. The last measure indicates the percentage of time subjects spent in seven arbitrarily defined concentric circles centered around the average COP in radial increments of 5 mm. The range of the COP was smaller in the self-triggered than in the reactive condition (30 vs. 35 mm, F(1,4) = 8.37, P , 0.05). No significant difference was observed for the displacement of the COP (74.4 vs. 76 mm, P . 0.05). Fig. 3 illustrates the percentage of time spent in the seven areas centered around the average COP under the two conditions of movement execution. Subjects spent more time around the COP in the self-triggered than in the reactive condition (68 vs. 58% of time within an area of 10 mm around the COP). The results of the present experiment clearly show that APAs were longer in the self-triggered than in the reactive condition and that postural stability was greater in the selftriggered than in the reactive condition. This confirmed results of previous experiments [7]. Results also show that the sequence of activation of the three postural muscles was similar but that the timing was different in the self-triggered
Fig. 1. Illustration, for a typical subject, of the superposition of five acceleration-time traces (Acc) and the corresponding averaged EMG signals (D, Anterior Deltoı¨dus; TFLc, contralateral Tensor Fascia Latae; STi, ipsilateral Semitendinosus; Gi, ipsilateral Gastrocnemius) for the reactive (left traces) and self-triggered (right traces) conditions. For illustration purposes, all signals are synchronized on the EMG onset of the focal muscle (Anterior Deltoı¨dus). The vertical dotted lines indicate the onset of the postural and focal muscles.
V. Nougier et al. / Neuroscience Letters 260 (1999) 109–112
Fig. 2. Illustration of the Condition × Delay interaction. Negative values indicate that activation of postural muscles preceded activation of the focal muscle.
and reactive conditions. More precisely, in the reactive condition the three postural muscles were activated within 10 ms, that is, almost simultaneously. In the self-triggered condition, the postural muscles were clearly activated one after the other, starting with the Semitendinosus, following with the Tensor Fascia Latae and then the Gastrocnemius. These observations suggest the existence of two different modes of control for intentionally raising the limb at a given velocity. In the reactive condition, the coordination of posture and movement was based on a time-locked strategy. The anticipation of arm raising was short and the postural muscles were activated almost in synchronization. When the moment of response initiation is not predictable, this is probably the easiest way to program motor commands within a short time, since the coordination of posture and movement and motor output may be triggered by a simultaneous and unique central command. This is reminiscent of experiments manipulating similar conditions of movement initiation for synchronizing a simultaneous finger and heel movement [1,2] or jaw and right foot movement [6]. Conversely, in the self-triggered condition the arm raising was mainly based on a representation of the movement and of the necessary coordination between posture and movement. According to this ‘goal image’ of the movement [13], a sequencing strategy was adopted for defining a precise timing of the afferent commands sent to the postural and focal muscles respectively. From that point of view, analysis of the COP displacements showed interesting results. A smaller range of the COP was observed in the self-triggered than in the reactive condition but no difference was observed for the overall displacement of the COP. These observations are partially contradictory with those of recent experiments [7]. In these experiments, subjects executed arm movements in a reactive and in a self-paced condition. For the first 100 ms, a smaller COP displacement was observed for the self-paced than for the reactive condition. For the overall movement, no difference in postural stability was observed between the two conditions. The results of the present experiment suggest that subjects had a more stable posture in the self-trig-
111
Fig. 3. Mean percentage of time spent in the seven concentric areas centered around the average COP in radial increments of 5 mm, for the reactive and self-triggered conditions. Modulation of anticipatory postural adjustments.
gered than in the reactive condition, as shown by the smaller range of the COP oscillations. More specifically, in the reactive condition, subjects showed COP oscillations of larger amplitude than in the self-paced condition, but the displacement of the COP was similar in the two conditions. It remains, however, that subjects spent more time near the average COP in the self-triggered than in the reactive condition. This suggests that two different postural strategies were used for executing a similar intentional movement. Under time pressure, the central nervous system clearly delays the initiation of APAs. These delayed APAs result in a less stable posture. Riehle and Requin [11] proposed that two mechanisms are responsible for the directional preparation of aiming movements. One could be responsible for a ‘presetting’ mechanism through a progressive increase of excitability of the neurons involved in the specific programming operations of movement direction. The second one could be responsible for a ‘preprocessing’ mechanism in which the movement would be partially or totally specified according to the precued information about movement direction. The results of the present experiment suggest that only the presetting mechanism would be involved in the preparation of arm raising in the reactive condition. The specification of muscles parameters (postural and focal muscles) would then occur almost simultaneously. In the self-triggered condition, the preprocessing mechanism would also be involved prior to movement initiation, allowing a differentiated specification of muscles commands. In conclusion, these results support the idea that intentional movements can be triggered by different timing strategies according to the context within which the intention can be expressed. [1] Bard, C., Paillard, J., Lajoie, Y., Fleury, M., Teasdale, N., Forget, R. and Lamarre, Y., Role of afferent information in the timing of motor commands: a comparative study with a deafferented patient, Neuropsychologia, 30 (1992) 201–206.
112
V. Nougier et al. / Neuroscience Letters 260 (1999) 109–112
[2] Bard, C., Teasdale, N., Fleury, M., Paillard, J. and Lajoie, Y., Self-induced versus reactive triggering of synchronous hand and heel movements in young and old subjects. In Requin, J. and Stelmach, G.E. (Eds), Tutorials in Motor Neuroscience, Kluwer Academic, Dordrecht, 1991, pp. 189–196. [3] Benvenuti, F., Panzer, V., Thomas, S. and Hallett, M., Kinematic and EMG analysis of postural adjustments associated with fast elbow flexion movements. In Brandt, T., Paulus, W., Bles, W., Dieterich, M., Krafczyk, S. and Straube, A. (Eds.), Disorders of Posture and Gait, Thieme, Stuttgart, 1990, pp. 137–141. [4] Bouisset, S. and Zattara, M., Postural muscular activities and intentional movements, Med. Sport Sci., 26 (1987) 163–173. [5] Bouisset, S. and Zattara, M., Anticipatory postural adjustments and dynamic asymmetry of voluntary movement. In Gurfinkel, M., Ioffe, M.E., Massion, J. and Roll, J.P. (Eds.), Stance and Motion: Facts and Concepts, Plenum, New York, 1988, pp. 177–183. [6] Devanne, H. and Maton, B., Role of proprioceptive information in the temporal coordination between joints, Exp. Brain Res., 119 (1998) 58–64. [7] De Wolf, S., Slijper, H. and Latash, M.L., Anticipatory postural
[8]
[9] [10]
[11]
[12]
[13]
adjustments during self-paced and reaction-time movements, Exp. Brain Res., 121 (1998) 7–19. Hugon, M., Massion, J. and Wiesendanger, M., Anticipatory postural changes induced by active unloading and comparison with passive unloading in man, Pflu¨gers Arch., 393 (1989) 292–296. Massion, J., Movement, posture and equilibrium: Interaction and coordination, Prog. Neurobiol., 38 (1992) 35–56. Paillard, J., Bard, C. and Fleury, F., Synchronizing hand and foot movement in a projective or reactive mode: two contrasting schedules of motor command, Soc. Neurosci. Abstr., (1989) 604. Riehle, A. and Requin, J., Monkey primary motor and premotor cortex: single-cell activity related to prior information about direction and extent of an intended movement, J. Neurophysiol., 61 (1989) 534–549. Viallet, F., Massion, J., Massarino, R. and Khalil, R., Coordination between posture and movement in a bimanual load lifting task: putative role of a medial frontal region including the supplementary motor area, Exp. Brain Res., 88 (1992) 674–684. Teuber, H.L., Key problems in the programming of movements, Brain Res., 71 (1974) 553–568.
Modulation of anticipatory postural adjustments in a reactive and a self-triggered mode in humans Vincent Nougier a ,*, Normand Teasdale b, Chantal Bard b, Michelle Fleury b a
Laboratoire Sport et Performance Motrice, Universite´ Joseph Fourier-Grenoble 1, BP 53, 38041 Grenoble cedex 9, France b Laboratoire de Performance Motrice Humaine, Universite´ Laval, Que´bec, Canada Received 21 October 1998; received in revised form 26 November 1998; accepted 26 November 1998
Abstract Five subjects raised their preferred arm until horizontal in one of two experimental conditions: (1) in response to a visual signal (reactive condition), and (2) in a self-triggered condition. In both conditions, subjects were instructed to execute the movement at approximately 80% of their maximal velocity, such that all movements were nearly similar. EMG activity was recorded in a focal muscle (Anterior Deltoidus) and in three postural muscles (ipsi-lateral Gastrocnemius, contra-lateral Tensor Fascia Latae and ipsi lateral Semitendinosus) known to be activated prior to the focal muscle. Results showed greater anticipatory postural adjustments in the self-triggered than in the reactive condition for the three postural muscles. It is suggested that similar intentional movements can be triggered by different timing strategies. 1999 Elsevier Science Ireland Ltd. All rights reserved.
Keywords: Anticipatory postural adjustments; Information processing; Human
It is now well established that posture and movement are highly integrated and require a good synchronization of both mechanisms [9]. More precisely, anticipatory postural adjustments (APAs) are generally observed when a movement has to be performed, as for example when raising a limb [4] or when voluntary unloading the forearm in a bimanual load lifting task [8,12]. In these intentional tasks, the muscles involved in the control of posture are activated prior to the muscles directly involved in the limb movement. The APAs allow to produce a shift of the center of gravity in the direction opposite to that of the focal movement, in order to compensate for the expected desequilibrium [4]. Intentional movements, however, can be performed in two conditions, at least: a reactive condition in response to an external signal and a self-triggered condition in which movement initiation is self-determined [2,10]. Previous studies investigated the onset of the APAs in a reaction time versus a self-paced condition of movement execution [3,5,7]. The results of these experiment were rather contradictory regarding the relative timing of the * Corresponding author. Tel.: +33 4 76514195; fax: +33 4 76514469; e-mail: [email protected]
0304-3940/99/$ - see front matter PI I : S0304- 3940(98) 00961- 6
APAs and the focal movement in the two conditions. One main reason was probably that the execution of the focal movement was not similar across the conditions and from one experiment to another. The purpose of the present experiment was to investigate the coordination of posture and movement in a reactive and self-triggered condition of movement initiation. To better isolate the effect of condition of movement initiation, a particular attention was devoted to a similar execution of the focal movement. Shorter APAs were expected in the reactive than in the self-triggered condition. As a result, a greater postural stability was also expected in the self-triggered than in the reactive condition. Five subjects (three right-handed and two left-handed), aged 26–37 years (mean age 32 years) participated in the experiment on a voluntary basis. Subjects stood feet together on a force platform. (KISTLER model 9284) which allowed measuring the displacement of the center of foot pressure. All signals were sampled at 50 Hz and then filtered with a second-order Butterworth filter (10 Hz lowpass cut-off frequency with dual pass to remove phase shift). Four prespaced (2.5 cm) Ag-AgCl surface electrodes were fixed to the central portion of respectively the Anterior Deltoı¨dus of the preferred hand, the ipsi-lateral Gastrocne-
1999 Elsevier Science Ireland Ltd. All rights reserved.
110
V. Nougier et al. / Neuroscience Letters 260 (1999) 109–112
mius, the contralateral Tensor Fascia Latae and the ipsi lateral Semitendinosus. The Anterior Deltoı¨dus was the main focal muscle of the movement (raising the arm). The other three muscles were considered as postural muscles. In a similar task, they were activated prior to the focal muscle, demonstrating the existence of APAs [4]. The electromyographic (EMG) signal was preamplified at the source (35 × ), filtered with a time constant of 2.5 ms, and bandpassed between 20 Hz and 4 kHz. In addition, an accelerometer was fixed on the external face of the hand. Force signals and accelerometer signal were collected at 500 Hz (12 bit A/D converter). The accelerometer was connected to an oscilloscope, such that the acceleration-time traces were stored and compared from trial to trial. When the trace deviated from the reference acceleration signal, the trial was rejected. Once having stabilized their posture on the force platform, subjects raised their preferred arm until horizontal, holding a 500 g weight in the hand. The arm raising was executed at a constant speed from trial to trial in two experimental conditions. In the reactive condition, subjects performed the movement in response to a visual signal (red light emitting diode). The onset of the response signal occurred randomly within 4 s, once subjects declared to be ready. It remained on until movement completion. In the self-triggered condition, subjects executed the movement whenever they were ready, within a 4 s period. In both conditions, subjects were instructed to execute the movement approximately at 80% of their maximal velocity, such that all movements were very similar. The acceleration-time traces served to control the similarity of the movements both in amplitude and time. These acceleration-time traces were compared from trial to trial via an oscilloscope. All trials which did not reach the criteria were immediately rejected (10% of the trials approximately). Subjects performed 20 correct trials for each condition. For all subjects, the reactive condition was presented first. The main dependent measure was the delay between EMG onset of the focal muscle and EMG onset of the three postural muscles. Delay was negatively signed when activation of the postural muscle preceded activation of the focal muscle, that is when an APA occurred. Fig. 1 illustrates, for a typical subject, the superimposition of five acceleration-time traces and the corresponding EMG signals for the two conditions. For illustration purposes, all signals are synchronized on the EMG onset of the focal muscle (Anterior Deltoı¨dus). A two-conditions × threemuscle analysis of variance with repeated measures on both factors was applied to the data. The results showed main effects of condition (F(1,4) = 7.82, P , 0.05) and muscle (F(2,8) = 16.51, P , 0.001). Postural muscles were activated earlier for the self-triggered than for the reactive condition. Furthermore, the APA was different according to the postural muscle involved. It was longer for the Semitendinosus than for the Tensor Fascia Latae which in turn was longer than for the Gastrocnemius.
Results also showed a significant interaction of condition × muscle (F(2,8) = 4.66, P , 0.05). As illustrated in Fig. 2, the increased APA as a function of the postural muscle activated was more important in the self-triggered than in the reactive condition. Since the subjects’ task was to raise the arm, the main COP displacements were observed mainly in the anteroposterior plane. Three different measures of postural stability were analyzed. The range indicates the maximal excursion of the COP from its original baseline. The displacement is the cumulated distance over the sampling period, that is, the overall sequence of movement. The last measure indicates the percentage of time subjects spent in seven arbitrarily defined concentric circles centered around the average COP in radial increments of 5 mm. The range of the COP was smaller in the self-triggered than in the reactive condition (30 vs. 35 mm, F(1,4) = 8.37, P , 0.05). No significant difference was observed for the displacement of the COP (74.4 vs. 76 mm, P . 0.05). Fig. 3 illustrates the percentage of time spent in the seven areas centered around the average COP under the two conditions of movement execution. Subjects spent more time around the COP in the self-triggered than in the reactive condition (68 vs. 58% of time within an area of 10 mm around the COP). The results of the present experiment clearly show that APAs were longer in the self-triggered than in the reactive condition and that postural stability was greater in the selftriggered than in the reactive condition. This confirmed results of previous experiments [7]. Results also show that the sequence of activation of the three postural muscles was similar but that the timing was different in the self-triggered
Fig. 1. Illustration, for a typical subject, of the superposition of five acceleration-time traces (Acc) and the corresponding averaged EMG signals (D, Anterior Deltoı¨dus; TFLc, contralateral Tensor Fascia Latae; STi, ipsilateral Semitendinosus; Gi, ipsilateral Gastrocnemius) for the reactive (left traces) and self-triggered (right traces) conditions. For illustration purposes, all signals are synchronized on the EMG onset of the focal muscle (Anterior Deltoı¨dus). The vertical dotted lines indicate the onset of the postural and focal muscles.
V. Nougier et al. / Neuroscience Letters 260 (1999) 109–112
Fig. 2. Illustration of the Condition × Delay interaction. Negative values indicate that activation of postural muscles preceded activation of the focal muscle.
and reactive conditions. More precisely, in the reactive condition the three postural muscles were activated within 10 ms, that is, almost simultaneously. In the self-triggered condition, the postural muscles were clearly activated one after the other, starting with the Semitendinosus, following with the Tensor Fascia Latae and then the Gastrocnemius. These observations suggest the existence of two different modes of control for intentionally raising the limb at a given velocity. In the reactive condition, the coordination of posture and movement was based on a time-locked strategy. The anticipation of arm raising was short and the postural muscles were activated almost in synchronization. When the moment of response initiation is not predictable, this is probably the easiest way to program motor commands within a short time, since the coordination of posture and movement and motor output may be triggered by a simultaneous and unique central command. This is reminiscent of experiments manipulating similar conditions of movement initiation for synchronizing a simultaneous finger and heel movement [1,2] or jaw and right foot movement [6]. Conversely, in the self-triggered condition the arm raising was mainly based on a representation of the movement and of the necessary coordination between posture and movement. According to this ‘goal image’ of the movement [13], a sequencing strategy was adopted for defining a precise timing of the afferent commands sent to the postural and focal muscles respectively. From that point of view, analysis of the COP displacements showed interesting results. A smaller range of the COP was observed in the self-triggered than in the reactive condition but no difference was observed for the overall displacement of the COP. These observations are partially contradictory with those of recent experiments [7]. In these experiments, subjects executed arm movements in a reactive and in a self-paced condition. For the first 100 ms, a smaller COP displacement was observed for the self-paced than for the reactive condition. For the overall movement, no difference in postural stability was observed between the two conditions. The results of the present experiment suggest that subjects had a more stable posture in the self-trig-
111
Fig. 3. Mean percentage of time spent in the seven concentric areas centered around the average COP in radial increments of 5 mm, for the reactive and self-triggered conditions. Modulation of anticipatory postural adjustments.
gered than in the reactive condition, as shown by the smaller range of the COP oscillations. More specifically, in the reactive condition, subjects showed COP oscillations of larger amplitude than in the self-paced condition, but the displacement of the COP was similar in the two conditions. It remains, however, that subjects spent more time near the average COP in the self-triggered than in the reactive condition. This suggests that two different postural strategies were used for executing a similar intentional movement. Under time pressure, the central nervous system clearly delays the initiation of APAs. These delayed APAs result in a less stable posture. Riehle and Requin [11] proposed that two mechanisms are responsible for the directional preparation of aiming movements. One could be responsible for a ‘presetting’ mechanism through a progressive increase of excitability of the neurons involved in the specific programming operations of movement direction. The second one could be responsible for a ‘preprocessing’ mechanism in which the movement would be partially or totally specified according to the precued information about movement direction. The results of the present experiment suggest that only the presetting mechanism would be involved in the preparation of arm raising in the reactive condition. The specification of muscles parameters (postural and focal muscles) would then occur almost simultaneously. In the self-triggered condition, the preprocessing mechanism would also be involved prior to movement initiation, allowing a differentiated specification of muscles commands. In conclusion, these results support the idea that intentional movements can be triggered by different timing strategies according to the context within which the intention can be expressed. [1] Bard, C., Paillard, J., Lajoie, Y., Fleury, M., Teasdale, N., Forget, R. and Lamarre, Y., Role of afferent information in the timing of motor commands: a comparative study with a deafferented patient, Neuropsychologia, 30 (1992) 201–206.
112
V. Nougier et al. / Neuroscience Letters 260 (1999) 109–112
[2] Bard, C., Teasdale, N., Fleury, M., Paillard, J. and Lajoie, Y., Self-induced versus reactive triggering of synchronous hand and heel movements in young and old subjects. In Requin, J. and Stelmach, G.E. (Eds), Tutorials in Motor Neuroscience, Kluwer Academic, Dordrecht, 1991, pp. 189–196. [3] Benvenuti, F., Panzer, V., Thomas, S. and Hallett, M., Kinematic and EMG analysis of postural adjustments associated with fast elbow flexion movements. In Brandt, T., Paulus, W., Bles, W., Dieterich, M., Krafczyk, S. and Straube, A. (Eds.), Disorders of Posture and Gait, Thieme, Stuttgart, 1990, pp. 137–141. [4] Bouisset, S. and Zattara, M., Postural muscular activities and intentional movements, Med. Sport Sci., 26 (1987) 163–173. [5] Bouisset, S. and Zattara, M., Anticipatory postural adjustments and dynamic asymmetry of voluntary movement. In Gurfinkel, M., Ioffe, M.E., Massion, J. and Roll, J.P. (Eds.), Stance and Motion: Facts and Concepts, Plenum, New York, 1988, pp. 177–183. [6] Devanne, H. and Maton, B., Role of proprioceptive information in the temporal coordination between joints, Exp. Brain Res., 119 (1998) 58–64. [7] De Wolf, S., Slijper, H. and Latash, M.L., Anticipatory postural
[8]
[9] [10]
[11]
[12]
[13]
adjustments during self-paced and reaction-time movements, Exp. Brain Res., 121 (1998) 7–19. Hugon, M., Massion, J. and Wiesendanger, M., Anticipatory postural changes induced by active unloading and comparison with passive unloading in man, Pflu¨gers Arch., 393 (1989) 292–296. Massion, J., Movement, posture and equilibrium: Interaction and coordination, Prog. Neurobiol., 38 (1992) 35–56. Paillard, J., Bard, C. and Fleury, F., Synchronizing hand and foot movement in a projective or reactive mode: two contrasting schedules of motor command, Soc. Neurosci. Abstr., (1989) 604. Riehle, A. and Requin, J., Monkey primary motor and premotor cortex: single-cell activity related to prior information about direction and extent of an intended movement, J. Neurophysiol., 61 (1989) 534–549. Viallet, F., Massion, J., Massarino, R. and Khalil, R., Coordination between posture and movement in a bimanual load lifting task: putative role of a medial frontal region including the supplementary motor area, Exp. Brain Res., 88 (1992) 674–684. Teuber, H.L., Key problems in the programming of movements, Brain Res., 71 (1974) 553–568.