| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
Submitted 9 December 2004; accepted in final form 9 February 2005
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
|---|
10 ms (Hore et al. 1995
; Timmann et al. 2001) and very skilled subjects with a variability of 5 ms (Jegede et al. 2005). Extrapolating these results to pitching in baseball revealed that a timing precision of 1–2 ms is needed to consistently hit the strike zone (cf., Hore et al. 2002). This fits with theoretical calculations that indicated that a timing precision of 1 ms is needed for very great accuracy in throwing (Calvin 1983; Chowdhary and Challis 1999). In keeping with this, we previously found that high and low ball inaccuracies on the target were not correlated with variability in rotations at the shoulder, elbow or wrist, but with variability (errors) in the timing of ball release (Hore et al. 1996a). Similarly, in throws made with the nondominant arm and in throws made by cerebellar subjects, the greater ball inaccuracy on the target was attributed to larger errors in the timing of the central command that initiated finger opening (Hore et al. 1996b; Timmann et al. 1999). Although there appears to be general acceptance that the cerebellum contributes to the achievement of precision in "timing," there are no specific proposals as to how this would occur for finger opening in throwing.
An alternative idea to a timing mechanism is that finger opening could be based on an internal positional representation of the throw. Some years ago Cordo and colleagues suggested that the trigger for finger opening in a throw could be proprioceptive feedback from elbow extension (Cordo 1990; Cordo et al. 1994). However, for overarm throws, changing proprioceptive feedback, e.g., by blocking elbow extension, did not change the occurrence or latency of finger opening (Hore et al. 1999a). In agreement, the latency of finger opening from onset of wrist flexion or elbow extension was too short for either to have triggered finger opening, and there was no correlation between timing of shoulder joint rotations and timing of finger opening. This led to the conclusion that finger opening is likely controlled centrally. Although these results indicated that proprioceptive feedback is too slow for fast overarm throwing, the possibility remains that this feedback could be used by subjects who are learning to throw. According to this mechanism, as they develop throwing speed a point will be reached where there is no longer sufficient time for sensory feedback, e.g., from elbow extension, to control finger opening. At this point finger opening could be controlled, not by sensory information about elbow extension, but by a feedforward positional representation of this same joint rotation. Alternatively, finger opening could be based on a feedforward positional representation of handpath in space (Hore et al. 1999a) because in throwing, it is the motion of the hand in space that determines the flight of the ball.
The objective was to test the hypothesis that finger opening is based on an internal positional representation of the throw. The hypothesis was investigated by determining whether finger extension position during finger opening maintains a constant relation with elbow extension position (in joint space), or with hand angular position, in throws of different speeds.
|
METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
|---|
The experiments, which were approved by the local ethics review board, were performed on a total of 12 right-handed male adults aged 20–24 who gave their informed consent. All subjects considered themselves to be skilled throwers, and all had played recreational or competitive baseball. There were two series of experiments. In the first, eight subjects sat on a chair with the trunk fixed by straps over the shoulder (subjects Sm, Fs, Sn, Ob, Oc, Tl, Bs, Gy). This enabled us to investigate mechanisms of control that were associated with arm-only throws. In the second series, eight subjects threw from a standing position so we could determine whether results were similar for more natural throws that involved body and arm motion. Four of the original subjects (Ob, Oc, Tl, Gy) and four new subjects (Ps, Ln, Ld, Ry) were studied. In the standing situation, the left foot was 
45 cm in front of the right foot, and both feet were kept relatively stationary, i.e., there was no baseball wind-up. In both series, subjects threw with a natural arm motion that involved forward-left horizontal motion of the upper arm. They threw baseballs (150 g) at a central target square (6 x 6 cm) at about eye height that was 3.1 m from the sternum in the sitting throws and about the same distance away at ball release in the standing throws. The central (aimed) target was on a grid of numbered target squares (each 6 x 6 cm), 9 squares wide x 27 high. Each throw was scored for accuracy by the subject calling out the number of the square that was hit. In both series, subjects made 30 medium-speed, 30 slow, and 30 fast throws in that order. Subjects were instructed to throw at a consistent speed and accurately. Ball speed was measured with a radar gun (Stalker professional Sports radar—sampling rate: 100/s). Ball release was measured by two pressure-sensitive microswitches (triggers) that were attached to the front of the distal and proximal phalanges of the middle finger. Subjects were instructed to grip the ball such that they applied pressure to the proximal switch and to release the ball from the middle finger so that the ball rolled over the distal switch. The accuracy of the distal microswitch was verified by comparing it with the time of the start of finger flexion after finger extension, which is a moment that is known to correlate with departure of the ball from the fingertip (e.g., Hore et al. 1999b).
Measurement of finger opening
Different parameters of opening (extension) at the proximal interphalangeal joint (PIJ) were measured. Onset was measured as the moment when the velocity of this joint rotation crossed a threshold of 200°/s. This was about 1/10 the velocity of this joint motion in the fast standing throws. A high threshold was used so that small fluctuations in finger motion in some subjects, that were unrelated to finger opening, were not measured as finger opening. Overall amplitude of PIJ extension was measured from the moment of onset to the moment of ball release. The relation between finger (PIJ) opening and hand angular position in space was measured about halfway through PIJ opening to ball release. The rationale for this is as follows. In an overarm throw, the hand travels on a flattened-arc path. To achieve accuracy, ball release must occur at the right point on this handpath. This is partly determined at the point on the handpath where the ball is first released from the handgrip. Once it is released from the handgrip, the ball rolls along the fingers until final release from the fingertip as the hand moves under the ball (Hore et al. 1999b). Final ball direction is established about halfway through this release period (Watts et al. 2004). Consequently, we measured finger opening at the PIJ about halfway through the ball release period because the fingers can affect ball direction up until this point.
Recording angular positions of arm segments
Angular positions of 10 finger, thumb, and arm segments were measured using the search-coil technique as described previously (e.g., Hore et al. 1992, 1996a). Although the search-coil technique records angular motions of arm segments robustly and with great precision, it does not record translational motion. Search coils were securely taped to the back of the three phalanges of the middle finger, the three thumb segments, the back of the hand, the back of the forearm proximal to the wrist, the lateral aspect of the upper arm, and the acromion process of the scapula. Subjects sat or stood in three orthogonal alternating magnetic fields of frequency 62.5, 100, and 125 kHz generated by 3 x 3 x 4-m Helmholtz coils. Coil voltages, sampled at 1,000 Hz, were used to calculate the simultaneous angular positions of each segment in three-dimensional space by means of algorithms described in Tweed et al. (1990). At the start of each experiment, a calibration was performed in which the upper arm was held horizontal at the side, the elbow was at 90°, and the forearm, hand and fingers were stationary in a vertical line with the palm forward (Fig. 1A). In the subsequent analysis, angular positions of arm segments in space and joint angles were given a value of 0° at this "reference position."
|
Two coordinate systems were used to describe arm motion measured with the search-coil technique. First, for the hand in space, we used a space-fixed coordinate system in which motions were described as components of rotations around axes aligned with the magnetic fields (Fig. 1A). For example, the vertical component of hand angular position in space was that component of rotation that occurred around the medial-lateral horizontal axis. The horizontal axis is seen in the behind and above views in Fig. 1A, and the vertical rotation is seen in the side view, i.e., forward-up. Second, arm motions were also described in terms of joint rotations by computing angular positions of arm segments with respect to the adjacent proximal segment. In this case, the axes were embedded in the proximal segment and rotated with it. It must be emphasized that joint rotations do not represent a component of motion around a space-fixed axis. Rather joint motions were computed as joint rotations. For example, elbow extension was motion of the forearm with respect to the upper arm irrespective of upper arm orientation. Similarly, shoulder joint rotations were motions of the upper arm with respect to motion of the scapula. Motions at the shoulder (Fig. 1B) were described as defined previously (e.g., Hore et al. 1996a). Shoulder roll was rotation of the upper arm around its own long axis, i.e., forward roll corresponds to shoulder internal rotation. Shoulder elevation was up-down rotation of the upper arm irrespective of azimuth. Azimuth was horizontal rotation of the upper arm, i.e., forward-left corresponds to horizontal adduction.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
|---|
Before investigating the central control of hand opening associated with ball release, it was first necessary to determine the relative contribution of finger and thumb to this opening. Across subjects there was no consistent rotation of a thumb joint that was associated with ball release. In some subjects, thumb rotations at individual joints were of very small amplitude (<5o). In other subjects, it was difficult to determine the onset of thumb rotation that was associated with ball release because thumb motion occurred during the backswing and early part of the forward throw as the hand gripped the ball with increasing force. Overall, our impression was that across throws of different speeds thumb and finger opened fairly closely together, but this could not be reliably quantified for all subjects.
In contrast, although rotations at the three finger joints also differed from subject to subject, all subjects showed relatively large extensions of the proximal interphalangeal joint (PIJ), and in all cases, this was strongly associated with onset of ball release from the hand. Figure 2A shows angular positions of the hand in space and the accompanying rotations at the distal interphalangeal joint (DIPJ), the PIJ, and the metacarpophalangeal joint (MCPJ) for single throws made by subjects Sm and Sn. These two subjects showed different patterns of finger joint rotations that resulted in markedly different magnitudes of rotation of the distal phalanx with respect to the hand (distal finger re hand). Nevertheless, in both cases, initiation of finger opening to release the ball was associated with extension of the PIJ. The time of onset of rotation at the PIJ (to a velocity threshold of 200°/s) is given by the short vertical line on the PIJ trace. The time of onset of uncoupling of the ball from the hand (i.e., the start of ball rolling along the fingers) is given by the signal from the microswitch on the proximal phalange of the middle finger (proximal trigger—long vertical line). When the time of onset of rotation at the PIJ (measured to the velocity threshold) for slow, medium, and fast throws was plotted against the time of onset of the proximal trigger (both measured to the moment when the hand was vertical in space), a strong correlation was found for both subjects (Fig. 2B). Similarly, across all subjects strong correlations were found between these parameters [the mean r value was sitting throws 0.90 ± 0.07 (SD), standing throws 0.84 ± 0.17]. This evidence is consistent with the scheme that opening of the hand to release the ball is produced at least in part by extension at the PIJ.
|
Insight into the central programming of extension at the PIJ may come from knowledge of the kinematics of motion at this joint in throws of different speeds. Figure 3, A–D, shows some kinematic parameters of 10 representative fast and slow throws made by subject Sm aligned on the moment of ball release (time 0). Compared with slow throws, fast throws have different time-varying hand angular positions in space (Fig. 3A), different elbow extensions (Fig. 3B), and different extension (opening) at the PIJ (Fig. 3C). In keeping with previous results (Hore et al. 1999b, 2001), the amplitude of extension at the PIJ remained relatively constant in throws of different speeds (Fig. 3C). The mean amplitudes to ball release of extension at the PIJ are shown for subject Sm in Fig. 4A (top left) for all slow (S), medium (M), and fast (F) throws. Mean ball speeds for 30 throws and SDs are shown in Fig. 4C. For subject Sm, the mean amplitudes were similar for throws of different speeds: slow, 29°; medium, 34°; fast, 33°. Across subjects there was no consistent difference in amplitude of PIJ extension for throws of different speeds (Fig. 4A). A repeated-measures ANOVA showed no effect of ball speed on finger amplitude (P = 0.14).
|
|
For each subject, there was variability in the magnitude of peak PIJ extension velocity for each set of throws of different speeds. For subject Sm, this can be seen in the plots of fast throws in Fig. 3E (
). To examine this more closely, we plotted the peak velocity of extension of the PIJ against its amplitude (to final ball release) for each set of throws of different speeds. Figure 5A shows that for subject Sm, there was a linear velocity-amplitude relation for each set of throws of a particular speed. Similar results were found for subjects Gy (Fig. 5B) and Ob (Fig. 5C), and in all subjects. At first sight, this relation might appear to reflect some saccade-like property of the central control of finger opening. However, this was not the case. Rather, the linear velocity-amplitude relation was simply a consequence of inherent variability in the velocity of finger extension and the fact that in throws of the same speed the ball takes the same time to roll along the finger. That is, given that a throw of a particular speed has a fixed time from onset of finger opening to final ball release, it follows that any variability in finger velocity over this fixed time will directly cause variability in finger amplitude. Thus finger velocity determined the amplitude of finger extension at ball release.
|
We next tested the hypothesis that finger opening is based on an internal positional representation of elbow extension. If this proposal is correct, it would be expected that finger opening would be closely related to elbow extension under different throwing conditions. To test this prediction, extension at the PIJ was plotted against elbow extension in throws of different speeds. To broaden the analysis, we also considered all arm joint rotations. Figure 6 shows for 10 fast and 10 slow throws made by subject Sm that no simple relation occurred for elbow extension (Fig. 6A), shoulder azimuth [B; horizontal adduction (see Fig. 1)] or shoulder forward roll (C; shoulder internal rotation). The differences for the fast, medium, and slow throws were quantified by measuring the angular positions of different arm joint rotations at a fixed angular position of finger opening that was about halfway through its range of motion to ball release. At this point in the throw, finger opening no longer influences ball direction (see METHODS). Figure 6A shows for subject Sm that at a fixed PIJ angular position of –16° (dashed horizontal line) elbow extension for the slow throws was 27°, whereas for the fast throws it was 42°. Figure 7 (elbow) shows, when all throws from this subject (Sm) were considered, that at the fixed PIJ angular position, there was a progressive increase from 25° (slow), to 34° (medium) to 44° (fast) throws. Similarly, across all subjects there was an increase in mean values for elbow extension (
) with an increase in ball speed. To determine whether differences occurred across subjects for the six different joint rotations at the three different speeds, we performed a repeated-measures ANOVA. Statistically significant differences (P < 0.05) were found for three of the six joint rotations: elbow extension (P = 0.02), shoulder azimuth (P = 0.01), and shoulder roll (P = 0.02) but not for wrist flexion (P = 0.43), radio-ulnar pronation (P = 0.17), and shoulder elevation (P = 0.66). Interestingly, when hand angular position in space was measured at the same fixed finger opening position, there was no difference across subjects for throws of different speeds (P = 0.99). In summary, no evidence was found for a simple constant relation between extension at the PIJ and elbow extension, shoulder azimuth, or shoulder roll in throws of different speeds.
|
|
To test the proposal that opening at the PIJ is based on an internal representation of hand angular position in space, we looked more closely at the relation between these two parameters. Traces of these two parameters for 10 fast and 10 slow throws made by subject Sm are shown in Fig. 3, A and C. For these same fast and slow throws, plots of angular positions of the hand in space against angular positions of the PIJ revealed considerable overlap of traces (Fig. 8A). Similarly, plots of these two parameters for fast and slow throws made by subject Fs (Fig. 8B) showed similar overlap. To determine whether these traces were different across all throws of different speeds, we measured the amplitude of the PIJ at a fixed hand angular position in space. One problem that was not allowed for in the analysis associated with Fig. 7 was the possibility of different initial positions of the PIJ that sometimes occurred in throws of different speeds due to different degrees of initial finger grip. To avoid this problem, we measured the amplitude of finger opening from its onset (at a velocity threshold of 200°/s; Fig. 8C, dashed line) to its amplitude at the fixed hand position in space. For example, Fig. 8C shows that the amplitude of finger opening for this single throw was 23° at a point where the hand in space was at an angle of –30° with respect to the hand vertical position (0°), i.e., before hand vertical. The mean amplitude of extension of the PIJ at a fixed hand angular position of –30° are shown in Fig. 9 for all throws at the three different speeds (S, slow; M, medium; F, fast) made by subject Sm. Across subjects no major difference can be seen in the PIJ amplitude. In keeping with this, a repeated-measures ANOVA showed that across subjects there was no statistically significant difference in amplitude of the PIJ for the three speeds of throw for hand angular positions of –30° (P = 0.84). Similarly, no differences were found for hand angular positions of –40° (P = 0.95) and –50° (P = 0.83).
|
|
The results described so far, which across subjects show no differences in the amplitude of opening of the PIJ for a fixed hand angular position in space, were obtained from throws made from the sitting position. However, it could be argued that this is an unnatural throwing position and that results may not apply for throws made from the more natural standing position. Furthermore, it is of interest to determine whether the relation between opening at the PIJ and hand angular position in space also applies in the more complex situation where hand angular position in space is affected by arm and body motion. Consequently, a second series of experiments was performed in which eight subjects threw from the standing position. Across subjects, analysis with repeated-measure ANOVAs showed that results were essentially the same as for the sitting throws. First, there was no effect of ball speed (Fig. 10D), on the amplitude of extension of the PIJ to ball release (P = 0.76; Fig. 10A). Second, there was an effect of ball speed on the velocity of extension at the PIJ (P < 0.001; Fig. 10B). And third, there was no effect of ball speed on the amplitude of the PIJ at hand angular positions in space of –30° (P = 0.80; Fig. 10C), –40° (P = 0.92), and –50° (P = 0.87) back from the position where the hand was vertical in space. In summary, across subjects at a fixed hand angular position in space there was no difference in the amplitude of extension at the PIJ joint for throws of different speeds.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
|---|
Ball release from the hand
Ball release from the handgrip occurs by opening of the thumb and finger. In the present experiments, we were unable to characterize the role of the thumb. This occurred for a variety of reasons including a small amplitude of motion at different thumb joints, variability of thumb motion across subjects, and the difficulty of distinguishing thumb motion associated with gripping the ball with increasing force from that associated with ball release. Nevertheless, strong correlations were found between ball release from the hand grip and extension at the PIJ.
It has previously been reported that in throws with balls of different weights that produced different back-forces on the fingers, the amplitude of the PIJ rotation to ball release was unchanged or smaller with the heavier balls (Hore et al. 1999b). In agreement, for both sitting throws (Fig. 4A) and standing throws (Fig. 10A), the amplitude of extension at the PIJ, from its onset to ball release from the fingertip, was similar for throws of different speeds. This is not necessarily the case for overall finger opening (distal phalanx rotation with respect to the hand) where amplitudes of the distal interphalangeal joint and the metacarpophalangeal joint can be different in throws of different speeds. This constant amplitude of the PIJ in throws of different speeds reflects a property of the central command that initiates ball release. A second and related property of the central command to the fingers comes from the finding that the velocity of opening (extension) of the PIJ was proportional to the speed of the throw. This was observed in sitting throws (Fig. 4B) and more strongly in standing throws (Fig. 10B).
Control of finger motion in arm-finger tasks: a timing or spatial mechanism?
Few would disagree with the statement that fast and accurate overarm throwing requires precise timing. In keeping with this idea, we have reported that ball inaccuracy on the target in fast throws made by skilled subjects results from inappropriate timing of onset of finger rotations with respect to rotations of other arm joints and thus to inappropriate timing of ball release (Hore et al. 1996a). This finding, and the suggestion that finger opening is based on a central mechanism that controls timing, is a consequence of measuring throwing motions in the time domain. But whether the underlying central control is based on a timing (clock-like) mechanism or on a spatial mechanism is unclear. The present results have ruled out one extreme form of the timing hypothesis in which a clock-like timer (say beating at 1,000 times/s) triggers a step-like (ballistic) finger opening at the right moment in the throw (cf. Hore et al. 2002). This is because of the finding that the speed of the PIJ opening was not ballistic but was proportional to the speed of the throw. However, this finding does not disprove all timing hypotheses because schemes involving a central timing mechanism could conceivably be proposed in which finger opening would have this speed-sensitive property.
The objective of the present study was to test the hypothesis that finger opening is generated by a spatial controller. Support for this hypothesis came from the observation that there was a similar relation for throws of different speeds (Fig. 8, A and B) between extension at the PIJ and the vertical component of hand angular position in space, i.e., that hand component that occurred around the medial-lateral horizontal axis. This was demonstrated quantitatively by showing that at a fixed hand angular position in space there was a similar PIJ amplitude for slow, medium and fast throws. This was true for both sitting throws (Fig. 9) and standing throws (Fig. 10C). This relation would only apply for throws of different speeds to a near target where there was minimal difference in the time of the ball drop due to gravity and thus minimal difference in the hand angular paths. The consequence of this relation is that for hand angular position and extension at the PIJ, a fast throw was the same as a slow throw sped-up.
The idea of a spatial controller is consistent with the current view of reaching and grasping, which like throwing, has two separate phases: a transport phase in which the hand travels on a predetermined path, and a grasp phase that involves finger motion. Jeannerod (1981) initially proposed that arm transport and finger grasp were controlled by independent visuomotor channels: the reach component used information about the target in egocentric space, whereas the grasp component used information about the target to preshape an appropriate grasping configuration. Although independent, these two channels were thought to be synchronized together. Further studies emphasized the strong temporal relationship between the two channels (e.g., Hoff and Arbib 1993; Jeannerod 1984; Marteniuk et al. 1990; Wallace and Weeks 1988; Wallace et al. 1990). However, Haggard and Wing (1991, 1995) have made an alternative proposal in which control occurs by spatial coupling between the two components, i.e., the grasp aperture is modulated based on the distance between the hand and the target. Initial support for this idea came from the observation that following perturbation of the arm, there was an adjustment of grasp aperture that returned the movement to the same spatial relation between the two variables that occurred in normal trials. This was described as a state-space coordination, i.e., a coordinated system in which information about the state of one component (the arm) is used in the control of the second component while the movement is in progress. In more recent studies, arm transport was changed by requiring subjects to perform curved arm movements over an intermediate point (Haggard and Wing 1998) or to pass over an obstacle (Alberts et al. 2002). In both cases, changes in arm transport affected grasp formation in a way that was consistent with a spatial controller.
In throwing, the invariant spatial relation between hand angular position in space and extension at the PIJ for throws of different speeds occurred irrespective of whether subjects threw from the sitting position where the trunk was fixed by straps over the shoulder or from the standing position where the trunk was free to move. Similarly, in the counterpart experiments for reaching and grasping, the length of the handpath between peak aperture of finger opening and contact of the object (aperture-closure distance) also remained invariant regardless of whether the hand was transported by arm, trunk, or both (Wang and Stelmach 1998) and regardless of the speed of the movement (Wang and Stelmach 2001).
Timing of ball release by a spatial controller in throwing
How does the CNS time finger opening and ball release to achieve accuracy in throws made at spatially different targets at different speeds? We previously found for throws of the same speed to spatially different targets in the sagittal plane (high-low and near-far) that the timing of ball release was the same for all targets (Watts et al. 2004). We now demonstrate that for throws of different speeds to the same near target (where different times of ball drop due to gravity are minimized) that accurate timing of ball release can be produced by an invariant spatial relation between hand angular path and finger opening. It follows that the timing accuracy of ball release to all targets at all speeds could potentially be controlled by two mechanisms. The first mechanism would calculate the direction (orientation) of the translational handpath. Orientation of the translational handpath in the vertical plane would require knowledge of the target height and an estimate of the amplitude of the ball drop due to gravity. The latter estimate could be calculated from the target distance and throwing speed. In sitting throws, different handpath orientations in the vertical plane were produced by different angular orientations of the upper arm in space (Watts et al. 2004). The second mechanism would calculate finger opening based on changes in hand angular position, i.e., hand angular path irrespective of hand angular starting position. Such a handpath positional signal could come from integration of a feedforward hand angular velocity signal or from feedforward information about upcoming rotations at shoulder, elbow, and wrist.
It is proposed that precise timing of ball release follows from accurate execution of these two spatial mechanisms. Conversely, inaccuracy in timing of ball release (and inaccuracy in ball impact on the target) would result, either from error in calculating the handpath translational orientation or from error in matching finger opening to hand angular position. Put another way, it is proposed that ball inaccuracy does not result from disorder in a "timing" mechanism, i.e., from disorder in a clock-like mechanism in which finger opening occurs on the beat of a high-frequency (e.g., 1,000/s) clock (see Keating and Thach 1995 for evidence against the idea that the inferior olive acts as a 10/s clock that triggers onset of all movement). Rather, it is proposed that disorders in timing of ball release in throwing result from disorders in operation of a central spatial controller.
Role of the cerebellum
We have previously found that cerebellar patients cannot throw accurately and that this is primarily correlated with variable timing of finger opening and ball release on the handpath (Timmann et al. 1999). It was argued that because finger opening is likely controlled by a central command, that these results implicated the cerebellum in timing the central command that initiates finger opening. This idea fitted with the widely held view that the cerebellum was involved in the control of a range of tasks that require precise timing. These included the production of skilled arm movements, eye-blink conditioning, learning in the VOR, increased variability in repetitive finger tapping, and perceptual tasks requiring timing (e.g., Braitenberg 1967; Ivry 1996, 1997; Jueptner et al. 1996; Keele and Ivry 1990; Raymond et al. 1996; Thompson et al. 1997). Similarly, an initial study of reach-to-grasp movements in cerebellar patients suggested that the variable kinematic parameters of the reach and the grasp, and the variable relationship between the two components, was due to a breakdown in the timing relationship between reach and grasp (Rand et al. 2000).
However, an alternative view that is based on the ideas of Thach et al. (1992) has been proposed for reach-to-grasp movements. According to this view, the breakdown in cerebellar patients in the coupling of reach-to-grasp movements resulted from an inability to combine reach and grasp movements into a single motor program (Zackowski et al. 2002). Given the importance of spatial parameters in the control of reach and grasp (e.g., Alberts et al. 2002; Haggard and Wing 1991, 1995; Rand et al. 2004; Saling et al. 1998), and the present findings that precise timing of ball release could occur by a spatial controller, it follows that cerebellar planning of arm-finger tasks may occur in the spatial domain. One suggestion is that the cerebellum adjusts the strength and timing of muscle contraction based on internal predictions made by a forward model of the sensory outcome of the motor command (e.g., Haruno et al. 2001; Miall and Reckess 2002; Wolpert and Kawato 1998). In such a scheme, forward models are used for feedforward control of complex arm movements. For example, it was previously suggested that paired forward and inverse models could generate an accurate overarm throw (Hore et al. 1999b). Based on these ideas, the present results suggest that for precise ball release in throwing the cerebellum predicts the course of the handpath, then matches (combines) finger opening to the predicted handpath.
Conclusion
Different schemes involving timing and spatial mechanisms could potentially be devised by which the CNS controls finger opening in fast and accurate overarm throws. The present finding, that the velocity of finger opening depends on the speed of the throw, appears to rule out one timing scheme in which finger opening is a step-like (ballistic) event that is triggered at the right moment in throws of different speeds. Rather, the results support the idea that precisely timed finger opening is controlled by a central spatial controller that matches (combines) angular positions of finger opening to the intended handpath. According to this view, precise timing of finger opening follows as an emergent property of a central spatial mechanism that is based on coordination of the multiple joints and muscles involved in the throw.
|
GRANTS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
|---|
|
ACKNOWLEDGMENTS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
|---|
|
FOOTNOTES |
|---|
Address for reprint requests and other correspondence: J. Hore, Dept. of Physiology and Pharmacology, University of Western Ontario, London, Ontario N6A 5C1, Canada (E-mail: jon.hore{at}fmd.uwo.ca)
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
|---|
Braitenberg V. Is the cerebellar cortex a biological clock in the millisecond range? Prog Brain Res 25: 334–346, 1967.[Medline]
Calvin WH. A stone's throw and its launch window: timing precision and its implications for language and hominid brains. J Theor Biol 104: 121–135, 1983.[CrossRef][ISI][Medline]
Chowdhary AG and Challis JH. Timing accuracy in human throwing. J Theor Biol 201: 219–229, 1999.[CrossRef][ISI][Medline]
Cordo PJ. Kinesthetic control of a multijoint movement sequence. J Neurophysiol 63: 161–172, 1990.
Cordo P, Carlton L, Bevan L, Carlton M, and Kerr GK. Proprioceptive coordination of movement sequences: role of velocity and position information. J Neurophysiol 71: 1848–1861, 1994.
Haggard P and Wing AM. Remote responses to perturbation in human prehension. Neurosci Lett 122: 103–108, 1991.[CrossRef][ISI][Medline]
Haggard P and Wing A. Coordinated responses following mechanical perturbation of the arm during prehension. Exp Brain Res 102: 483–494, 1995.[ISI][Medline]
Haggard P and Wing A. Coordination of hand aperture with the spatial path of hand transport. Exp Brain Res 118: 286–292, 1998.[CrossRef][ISI][Medline]
Haruno M, Wolpert DM, and Kawato M. MOSAIC model for sensorimotor learning and control. Neural Comput 13: 2201–2220, 2001.
Hoff B and Arbib AM. Models of trajectory formation and temporal interaction of reach and grasp. J Mot Behav 25: 175–192, 1993.[ISI][Medline]
Hore J, Ritchie R, and Watts S. Finger opening in an overarm throw is not triggered by proprioceptive feedback from elbow extension or wrist flexion. Exp Brain Res 125: 302–312, 1999a.[CrossRef][ISI][Medline]
Hore J, Timmann D, and Watts S. Disorders in timing and force of finger opening in overarm throws made by cerebellar subjects. Ann NY Acad Sci 978: 1–15, 2002.
Hore J, Watts S, Leschuk M, and MacDougall A. Control of finger grip forces in overarm throws made by skilled throwers. J Neurophysiol 86: 2678–2689, 2001.
Hore J, Watts S, Martin J, and Miller B. Timing of finger opening and ball release in fast and accurate overarm throws. Exp Brain Res 103: 277–286, 1995.[ISI][Medline]
Hore J, Watts S, and Tweed D. Errors in the control of joint rotations associated with inaccuracies in overarm throws. J Neurophysiol 75: 1013–1025, 1996a.
Hore J, Watts S, and Tweed D. Prediction and compensation by an internal model for back forces during finger opening in an overarm throw. J Neurophysiol 82: 1187–1197, 1999b.
Hore J, Watts S, Tweed D, and Miller B. Overarm throws with the nondominant arm: kinematics of accuracy. J Neurophysiol 76: 3693:3704, 1996b.
Hore J, Watts S, and Vilis T. Constraints on arm position when pointing in three dimensions: Donders' law and the Fick gimbal strategy. J Neurophysiol 68: 374–383, 1992.
Ivry RB. The representation of temporal information in perception and motor control. Curr Opin Neurobiol 6: 851–857, 1996.[CrossRef][ISI][Medline]
Ivry R. Cerebellar timing systems. Int Rev Neurobiol 41: 555–573, 1997.[ISI][Medline]
Jeannerod M. Intersegmental coordination during reaching at natural visual objects. In: Attention and Performance IX, edited by Long J and Baddley A. Hillsdale, NJ: Erlbaum, 1981, p. 153–168.
Jeannerod M. The timing of natural prehension movements. J Mot Behav 16: 235–254, 1984.[ISI][Medline]
Jegede E, Watts S, Stitt L, and Hore J. Timing of ball release in overarm throws affects ball speed in unskilled but not skilled subjects. J Sports Sci In press.
Jueptner M, Flerich L, Weiller C, Mueller SP, and Diener HC. The human cerebellum and temporal information processing—results from a PET experiment. Neuroreport 7: 2761–2765, 1996.[ISI][Medline]
Keating JG and Thach WT. Nonclock behavior of inferior olive neurons: interspike interval of Purkinje cell complex spike discharge in the awake behaving monkey is random. J Neurophysiol 73: 1329–1340, 1995.
Keele SW and Ivry R. Does the cerebellum provide a common computation for diverse tasks? A timing hypothesis. Ann NY Acad Sci 608: 179–211, 1990.[ISI][Medline]
Marteniuk GG, Leavitt JL, MacKenzie CL, and Athenes S. Functional relationships between grasp and transport components in a prehension task. Hum Mov Sci 9: 149–176, 1990.[CrossRef]
Miall RC and Reckess GZ. The cerebellum and the timing of coordinated eye and hand tracking. Brain Cognit 48: 212–226, 2002.[CrossRef][ISI][Medline]
Rand MK, Shimansky Y, Stelmach GE, and Bloedel JR. Adaptation of reach-to-grasp movement in response to force perturbations. Exp Brain Res 154: 50–65, 2004.[CrossRef][ISI][Medline]
Rand MK, Shimansky Y, Stelmach GE, Bracha V, and Bloedel JR. Effects of accuracy constraints on reach-to-grasp movements in cerebellar patients. Exp Brain Res 135: 179–188, 2000.[CrossRef][ISI][Medline]
Raymond JL, Lisberger SG, and Mauk MD. The cerebellum: a neuronal learning machine? Science 272: 1126–1131, 1996.[Abstract]
Saling M, Alberts J, Stelmach GE, and Bloedel JR. Reach-to-grasp movements during obstacle avoidance. Exp Brain Res 118: 251–258, 1998.[CrossRef][ISI][Medline]
Thach WT, Goodkin HP, and Keating JG. The cerebellum and the adaptive coordination of movement. Annu Rev Neurosci 15: 403–442, 1992.[CrossRef][ISI][Medline]
Thompson RF, Bao S, Chen L, Cipriano BD, Grethe JS, Kim JJ, Thompson JK, Tracy JA, Weninger MS, and Krupa DJ. Associative learning. Int Rev Neurobiol 41: 151–189, 1997.[ISI][Medline]
Timmann D, Citron R, Watts S, and Hore J. Increased variability in finger position occurs throughout overarm throws made by cerebellar and unskilled subjects. J Neurophysiol 86: 2690–2702, 2001.
Timmann D, Watts S, and Hore J. Failure of cerebellar patients to time finger opening precisely causes ball high-low inaccuracy in overarm throws. J Neurophysiol 82: 103–114, 1999.
Tweed D, Cadera W, and Vilis T. Computing three-dimensional eye position quaternions and eye velocity from search coil signals. Vision Res 30: 97–110, 1990.[CrossRef][ISI][Medline]
Wallace SA and Weeks DL. Temporal constraints in the control of prehensile movement. J Mot Behav 20: 81–105, 1988.[ISI][Medline]
Wallace SA, Weeks DL, and Kelso JAS. Temporal constraints in reaching and grasping behavior. Hum Mov Sci 9: 69–93, 1990.
Wang J and Stelmach GE. Coordination among the body segments during reach-to-grasp action involving the trunk. Exp Brain Res 123: 346–350, 1998.[CrossRef][ISI][Medline]
Wang J and Stelmach GE. Spatial and temporal control of trunk-assisted prehensile actions. Exp Brain Res 136: 231–240, 2001.[CrossRef][ISI][Medline]
Watts S, Pessotto I, and Hore J. A simple rule for controlling overarm throws to different targets. Exp Brain Res 159: 329–339, 2004.[CrossRef][ISI][Medline]
Wolpert DM and Kawato M. Multiple paired forward and inverse models for motor control. Neurol Networks 11: 1317–1329, 1998.
Zackowski KM, Thach WT, and Bastian AJ. Cerebellar subjects show impaired coupling of reach and grasp movements. Exp Brain Res 146: 511–522, 2002.[CrossRef][ISI][Medline]
This article has been cited by other articles:
|
|
 |
|
  J. Diedrichsen, S. E. Criscimagna-Hemminger, and R. Shadmehr Dissociating Timing and Coordination as Functions of the Cerebellum J. Neurosci., June 6, 2007; 27(23): 6291 - 6301. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Hore, M. O'Brien, and S. Watts Control of Joint Rotations in Overarm Throws of Different Speeds Made by Dominant and Nondominant Arms J Neurophysiol, December 1, 2005; 94(6): 3975 - 3986. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||
), medium (
), and fast throws (
