• Neural Foundations of Handedness

    Findings from our laboratory have revealed substantial differences in coordination between the two arms in healthy individuals that arise from differential contributions of each cerebral hemisphere to movement of each arm. Based on these findings, we have proposed the dynamic dominance hypothesis, which attributes to the left hemisphere, anticipation of task dynamics, and to the right hemisphere, control of limb impedance, largely determining the final position of reaching and positional stability for holding objects while manipulating with the dominant arm. This hypothesis has been supported by studies that have examined interlimb differences in multijoint reaching (Sainburg and Kalakanis, 2000; Sainburg 2002; Bagesteiro and Sainburg, 2002a; Shabbott et al, 2008; Wang et al, 2007; Sainburg and Duff, 2006), targeted single joint movements (Bagesteiro and Sainburg, 2002b; Sainburg and Schaefer, 2004), and studies examining transfer of learning between the limbs (Sainburg and Wang, 2002, 2003, 2006, 2009). Our hypothesis leads to specific predictions about the coordination of the ipsilesional arm in patients with stroke. In collaboration with Dr. Kathleen Haaland, we have recently confirmed many of these predictions (Mutha et al, 2010, 2011a, 2011b; Schaefer et al, 2007, 2009a, 2009b; Haaland et al, 2009; 2011). This line of research has lead to current work that examines coordination deficits and recovery of function in both ipsilesional and contralesional arms of stroke patients (see below). We are currently examining the effect of motor lateralization on bilateral coordination (Wang et al, 2010; Wang and Sainburg, 2009; Mutha and Sainburg, 2009), when both arms are used in a single task, and have developed a simulation that incorporates our model of lateralization into a control scheme for unilateral movements.

  • Movement Deficits and Recovery of Function Following Stroke

    Recent studies on motor lateralization have revealed consistent differences in control strategies employed by the dominant and nondominant hemisphere/limb systems that could have implications for hemiplegic stroke patients. Studies in stroke patients have demonstrated deficiencies in the ipsilesional arm that reflect these distinctions, such that patients with right hemisphere damage tend to show deficits in positional accuracy, and patients with left hemisphere damage show deficits in trajectory control. Such deficits have been shown to impede functional performance, a problem amplified in patients who have severe dominant side hemiplegia and must learn to use the non-dominant arm as the primary manipulator for activities of daily living. The purpose of this line of research is to comprehensively examine the coordination deficits in the ipsilesional arm, following unihemispheric brain damage due to stroke. We employ experimental paradigms that have previously demonstrated differences in dominant and non-dominant coordination in healthy subjects Sainburg and Kalakanis, 2000; Sainburg 2002; Bagesteiro and Sainburg, 2002; Sainburg and Wang, 2002; Wang and Sainburg, 2003). In these multidirection reaching tasks, inverse dynamic analysis of segment torques, as well as, electromyography is used to compare differences in trajectory dynamics. Through these studies, we are better characterizing the motor capacities and impairments in the ipsilesional arm of unilateral lesioned stroke patients (Schaefer et al, 2007, 2009a, 2009b; Haaland et al, 2009; Schaefer et al, 2007). We are also beginning to examine techniques for facilitating recovery of motor function following stroke. We have recently elaborated the functional neuroanatomy underlying these lateralized processes (Mutha et al, 2010; 2011a; 2011b)

    Multisensory Integration for Reaching

    The aim of this research program is to discern the neural mechanisms underlying control of multijoint reaching movements in humans. We combine both psychophysical experiments and biomechanical simulations to determine the neural processes underlying control of the complex mechanics of the musculoskeletal system. Because of such dynamics, the relationships between muscle activation and movement kinematics are complex and non-linear. Studies in proprioceptively deafferented patients, who lack sense of joint position and movement, have allowed us to examine the role of different types of sensory information in controlling intersegmental coupling forces (Sainburg et al., 1993, 1995; Ghez and Sainburg, 1995). More recent work, in neurologically intact subjects, has confirmed that the nervous system uses sensory information to develop transient representations, or internal models, of musculoskeletal dynamics, in accord with task specific constraints (Sainburg, Kalakanis, and Ghez, 1999). Computer simulations suggest that such representations are utilized to take advantage of specific mechanical properties of the limb during movement planning (Kalakanis and Sainburg, 1999). Our findings (see Sarlegna and Sainburg, 2009) suggest that vision and proprioception contribute differentially to the movement planning process. In addition, recent research has indicated that even short latency spinal reflexes can be modulated by visual information that changes mid-course in a reaching movement (Mutha et al, 2008), and has revealed short-latency bilateral reflexes that emerge only when the two hands manipulate a common virtual object (Mutha and Sainburg, 2009)

    Motor Learning and Generalization

    The tendency for practice of a novel activity with one arm to affect subsequent performance with the other arm has previously been demonstrated for a number of tasks, such as finger tapping (Laszlo, Gaguley, and Bairstow ,1970), keyboard pressing (Taylor and Heilman ,1980), inverted and/or reversed writing (Parlow and Kinsbourne, 1989; 1990; Latash, 1999), figure drawing (Thut et al. 1996), and reaching during coriolis force perturbations (DiZio and Lackner, 1995), and during visuomotor displacements (Elliot and Roy, 1981; Imamizu and Shimojo, 1995). However, the mechanisms underlying this transfer are not well understood. Intermanual transfer of motor adaptation is thought to reflect the sharing of specific learned information between left and right arm control systems. Recent findings from our laboratory support the idea that initial training with one arm can improve subsequent adaptation with the other arm. However, different aspects of control appear to transfer in different directions: Opposite arm training improves the initial direction of dominant arm movements, whereas it only improves the final position accuracy of non-dominant arm movements. This suggests that the direction of transfer depends on the proficiency of the arm controller in question for specifying particular features of movement. Current studies suggest that other types of learning transfer differentially, such that adaptation to novel inertial loads transfers from the dominant to the nondominant arm. The mechanisms of this transfer are currently being probed. More recent work has examined how learning transfers across bimanual and unimanual task conditions (Wang and Sainburg, 2009), as well as differentiating the use of visual information for on-line corrections, as compared with between trial adaptations (Shabbott and Sainburg, 2009). We recently revealed limitations in generalization between unilateral and bilateral movements (Wang et al, 2010)