Two Laboratory Exercises Demonstrating Neural Adaptation: Eye-Hand Coordination and Anticipatory Postural Adjustments

Journal of Physical Therapy Education, Spring 2005 by Buford, John A

This brief manuscript describes two dynamic learning experiences in neuroscience designed to reinforce learning about neural plasticity. These activities require minimal equipment, are fun, and could be integrated within a basic science, clinical science, or clinical laboratory course in neurological rehabilitation.

Key Words: Motor control, Posture, Prism-adaptation, Neuroscience laboratory.

INTRODUCTION

Educators in physical therapy value active participation to facilitate learning.1,2 The creation of experiences that are practical for the instructor and educational for the students, however, is a challenge. Nonetheless, transformation of lecture segments into experiences can make teaching and learning more memorable and fun for the students and the teacher. In this brief report, two laboratory exercises are described that may help students understand adaptation, coordination, and anticipation as elements of motor control. The tasks performed by students for these demonstrations require multiple motor systems, but the focus of the demonstrations is cerebellar function.

DEMONSTRATION 1: EYE-HAND COORDINATION

The first activity, which was developed and described by others,3'4 is based on a prism adaptation experiment. This activity demonstrates how rapidly the normal nervous system can adapt eyehand coordination following a change in vision. A list of materials required and a basic procedure for this demonstration is provided in Table 1. For baseline performance, a student throws bean bags at a target while the class tracks the student's accuracy over about 30 trials. Then, the student dons a special pair of prismatic goggles that requires the eyes to deviate 15° to the right in order to focus on objects that are straight ahead. Initially, this gazeshift causes the student to throw to the right. With about 30-50 trials of practice, most subjects learn to throw on target. Once the individual has adapted and can throw accurately to the target despite the gaze-shift, the goggles are removed, causing the subject to throw left. Readaptation to natural eyehand coordination occurs after 20-30 more trials. This demonstration is always quite impressive, especially when students are reminded that, despite 20 or more years of functional throwing, their eyehand coordination changed dramatically in a matter of minutes. This experience helps students appreciate adaptation as a form of motor learning. Experiments reported in the scientific literature link this example of adaptation to neural plasticity specifically in cerebellar circuits.3,5 Critical reading of such literature is appropriate for advanced students.

DEMONSTRATION 2: ANTICIPATORY POSTURAL ADJUSTMENTS

In addition to adaptation, the cerebellum also contributes to coordination and anticipation.5 The prism adaptation experiment provides a clear example of control over eye-hand coordination. Impaired coordination due to cerebellar dysfunction (ataxia, arrhythmia, decreased fine-motor accuracy, and decomposition of movement) can be observed in cases of multiple sclerosis, cerebellar degeneration, or brainstem strokes. Clear examples of isolated problems with anticipatory motor control, however, are less common.

To demonstrate anticipation in normal motor control, a new activity was created based on the work of Horak.6 Subjects with intact postural responses are able to scale their reactions so that a larger perturbation elicits a larger reaction.6,7 Horak6 demonstrated that patients with cerebellar loss could not learn to scale their postural responses very well to platform perturbations with consistent velocities and varying amplitudes, even though they could adapt to perturbations with consistent amplitudes and varying velocities. Perturbations with consistent amplitudes and varying velocities did not require anticipation because the initial proprioceptive input was proportional to the response required. When the velocity was consistent, but the amplitude varied, however, anticipation was required because the initial proprioceptive input was not completely informative. Thus, patients with cerebellar loss did poorly at the task requiring anticipatory motor control.

After covering functions of the cerebellum in a lecture format, the laboratory experience helped emphasize the importance of anticipatory postural adjustments in motor control and motor learning. The laboratory exercise also introduced students to the various postural strategies used to maintain postural stability.7 For the demonstration, a student stands on a moveable platform and reacts to platform perturbations of two amplitudes (short and far) and two speeds (slow and moderate). These perturbations are presented in both blocked and random schedules,2 as detailed below. Student observers rate the postural response of the subject on a five point scale: 0 = no apparent postural disturbance, 1 = ankle strategy, 2 = hip strategy, 3 = stepping strategy, and 4 = falls (but is caught).

The subject should be a student volunteer who claims to have good balance and coordination and has no known history of orthopedic problems in the lower limbs. The subject wears a gait belt and is guarded by two other student volunteers (one on each side). The platform is a rolling furniture dolly with ropes at the front and rear ends. The instructor sits on the floor at the front end of the dolly, pulling the rope to move it forward as the student faces forward. A second student volunteer with good upper-body strength sits on the floor behind the dolly and provides tension on the rear rope to prevent the dolly from rolling out from underneath the subject. The guards keep their hands in place, ready to grab the gait belt if necessary. For each trial, the instructor says, "ready, set, go," and begins pulling on "go." A simple diagram of the setup is provided in Figure 1; a list of the requirements is provided in Table 2.