The neural foundations of handedness: insights from a rare case of deafferentation.

The role of proprioceptive feedback on motor lateralization remains unclear. We asked whether motor lateralization is dependent on proprioceptive feedback by examining a rare case of proprioceptive deafferentation (GL). Motor lateralization is thought to arise from asymmetries in neural organization, particularly at the cortical level. For example, we have previously provided evidence that the left hemisphere mediates optimal motor control that allows execution of smooth and efficient arm trajectories, while the right hemisphere mediates impedance control that can achieve stable and accurate final arm postures. The role of proprioception in both of these processes has previously been demonstrated empirically, bringing into question whether loss of proprioception will disrupt lateralization of motor performance. In this study, we assessed whether the loss of online sensory information produces deficits in integrating specific control contributions from each hemisphere by using a reaching task to examine upper limb kinematics in GL and five age-matched controls. Behavioral findings revealed differential deficits in the control of the left and right hands in GL and performance deficits in each of GL's hands compared with controls. Computational simulations can explain the behavioral results as a disruption in the integration of postural and trajectory control mechanisms when no somatosensory information is available. This rare case of proprioceptive deafferentation provides insights into developing a more accurate understanding of handedness that emphasizes the role of proprioception in both predictive and feedback control mechanisms.NEW & NOTEWORTHY The role of proprioceptive feedback on the lateralization of motor control mechanisms is unclear. We examined upper limb kinematics in a rare case of peripheral deafferentation to determine the role of sensory information in integrating motor control mechanisms from each hemisphere. Our empirical findings and computational simulations showed that the loss of somatosensory information results in an impaired integration of control mechanisms, thus providing support for a complementary dominance hypothesis of handedness.

Temporal and spatial aspects of sensory interactions during human fusional response.

Temporal and spatial aspects of sensory interactions during human fusional response were investigated using band-limited, 10th-derivative-of-Gaussian patterns confined to separate regions of the visual field. Experiments were performed to investigate the time course of sensory interactions using the horizontal sensory fusional amplitude (SFA) and the sensory fusional range (SFR) as measures of the interaction. The nature of sensory interactions across the spatial domain has been found to be a function of stimulus duration and time course. These interactions included both enhancements and reductions of SFAs as well as reductions and shifts in SFRs. Two functional components of sensory fusional interactions have become apparent. A fast component is manifested through a global reduction of SFAs while a slower component exhibits both enhancement and reduction of SFAs. The fast and slow components exhibit spatial summation; however, temporal summation within a local region of the visual field is not observed.

Experience with a partnership program for cardiac surgery at a regional military medical center.

A Partnership Program between USAF Medical Center, Wright-Patterson (WPAFB) and Miami Valley Hospital (MVH), Dayton, Ohio, was created through CHAMPUS to provide cardiac surgical services for eligible patients. During the first year of this program, 82 patients underwent 89 percutaneous transluminal coronary angioplasty (PTCA) procedures. Sixty-one patients underwent cardiac surgery at WPAFB, 50 were referred to MVH due to ineligibility or other reasons, and five were referred to other military or civilian hospitals. The program has been successful with low morbidity and mortality (3%). Cost savings for PTCAs was $241,853 and for cardiac surgery was $462,046.

Control strategies for the transition from multijoint to single-joint arm movements studied using a simple mechanical constraint.

Changes were studied in neuromotor control that were evoked by constraining the motion of the elbow joint during planar, supported movements of the dominant arm in eight normal human subjects. Electromyograph (EMG) recordings from shoulder and arm muscles were used to determine whether the normal multijoint muscle activity patterns associated with reaching to a visual target were modified when the movement was reduced to a single-joint task, by pinning the elbow to a particular location in the planar work space. Three blocks of 150 movements each were used in the experiments. Subjects were presented with the unconstrained task in the first and third blocks with an intervening block of constrained trials. Kinematic, dynamic, and EMG measures of performance were compared across blocks. The imposition of the pin constraint caused predictable changes in kinematic performance, in that near-linear motions of the hand became curved. This was followed by changes in limb dynamic performance at the elbow. However, changes in EMG activity at the shoulder lagged the kinematic changes substantially (by about 15 trials). The gradual character of the changes in EMG timing does not support a primary role for segmental reflex action in mediating the transition between multijoint and single-joint control strategies. Furthermore, the scope and magnitude of these changes argues against the notion that human motor performance is driven by the optimization of muscle- or joint-related criteria alone. The findings are best described as reflecting the actions of a feedforward adaptive controller that has properties that are modified progressively according to the environmental state.

Impedance control and internal model formation when reaching in a randomly varying dynamical environment.

We investigated the effects of trial-to-trial, random variation in environmental forces on the motor adaptation of human subjects during reaching. Novel sequences of dynamic environments were applied to subjects' hands by a robot. Subjects reached first in a "mean field" having a constant gain relating force and velocity, then in a "noise field," having a gain that varied randomly between reaches according to a normal distribution with a mean identical to that of the mean field. The unpredictable nature of the noise field did not degrade adaptation as quantified by final kinematic error and rate of adaptation. To achieve this performance, the nervous system used a dual strategy. It increased the impedance of the arm as evidenced by a significant reduction in aftereffect size following removal of the noise field. Simultaneously, it formed an internal model of the mean of the random environment, as evidenced by a minimization of trajectory error on trials for which the noise field gain was close to the mean field gain. We conclude that the human motor system is capable of predicting and compensating for the dynamics of an environment that varies substantially and randomly from trial to trial, while simultaneously increasing the arm's impedance to minimize the consequence of errors in the prediction.

Learning to move amid uncertainty.

We studied how subjects learned to make movements against unpredictable perturbations. Twelve healthy human subjects made goal-directed reaching movements in the horizontal plane while holding the handle of a two-joint robotic manipulator. The robot generated viscous force fields that perturbed the limb perpendicular to the desired direction of movement. The amplitude (but not the direction) of the viscous field varied randomly from trial to trial. Systems identification techniques were employed to characterize how subjects adapted to these random perturbations. Subject performance was quantified primarily using the peak deviation from a straight-line hand path. Subjects adapted their arm movements to the sequence of random force-field amplitudes. This adaptive response compensated for the approximate mean from the random sequence of perturbations and did not depend on the statistical distribution of that sequence. Subjects did not adapt by directly counteracting the mean field strength itself on each trial but rather by using information about perturbations and movement errors from a limited number of previous trials to adjust motor commands on subsequent trials. This strategy permitted subjects to achieve near-optimal performance (defined as minimizing movement errors in a least-squares sense) while maintaining computational efficiency. A simple model using information about movement errors and perturbation amplitudes from a single previous trial predicted subject performance in stochastic environments with a high degree of fidelity and further predicted key performance features observed in nonstochastic environments. This suggests that the neural structures modified during motor adaptation require only short-term memory. Explicit representations regarding movements made more than a few trials in the past are not used in generating optimal motor responses on any given trial.

Microchip technology in drug delivery.

The realization that the therapeutic efficacy of certain drugs can be affected dramatically by the way in which they are delivered has created immense interest in controlled drug delivery systems. Much previous work in drug delivery focused on achieving sustained drug release rates over time, while a more recent trend is to make devices that allow the release rate to be varied over time. Advances in microfabrication technology have made an entirely new type of drug delivery device possible. Proof-of-principle experiments have shown that silicon microchips have the ability to store and release multiple chemicals on demand. Future integration of active control electronics, such as microprocessors, remote control units, or biosensors, could lead to the development of a 'pharmacy on a chip,' ie 'smart' microchip implants or tablets that release drugs into the body automatically when needed.

Persistence of motor adaptation during constrained, multi-joint, arm movements.

We studied the stability of changes in motor performance associated with adaptation to a novel dynamic environment during goal-directed movements of the dominant arm. Eleven normal, human subjects made targeted reaching movements in the horizontal plane while holding the handle of a two-joint robotic manipulator. This robot was programmed to generate a novel viscous force field that perturbed the limb perpendicular to the desired direction of movement. Following adaptation to this force field, we sought to determine the relative role of kinematic errors and dynamic criteria in promoting recovery from the adapted state. In particular, we compared kinematic and dynamic measures of performance when kinematic errors were allowed to occur after removal of the viscous fields, or prevented by imposing a simulated, mechanical "channel" on movements. Hand forces recorded at the handle revealed that when kinematic errors were prevented from occurring by the application of the channel, recovery from adaptation to the novel field was much slower compared with when kinematic aftereffects were allowed to take place. In particular, when kinematic errors were prevented, subjects persisted in generating large forces that were unnecessary to generate an accurate reach. The magnitude of these forces decreased slowly over time, at a much slower rate than when subjects were allowed to make kinematic errors. This finding provides strong experimental evidence that both kinematic and dynamic criteria influence motor adaptation, and that kinematic-dependent factors play a dominant role in the rapid loss of adaptation after restoring the original dynamics.