Chou-Ching K. Lin

Time-course analysis of stretch reflexes in hemiparetic subjects using an on-line spasticity measurement system.

Spasticity after a stroke is usually assessed in a score form by subjectively determining the resistance of a joint to an externally imposed passive movement. This work presents a spasticity measurement system for on-line quantifying the stretch reflex of paretic limbs. Four different constant stretch velocities in a ramp-and-hold mode are used to elicit the stretch reflex of the elbow joint in spastic subjects. The subjects are tested at supine position with the upper limb stretched towards the ground, in contrast with the horizontally stretched movement used in other studies. By subtracting the baseline torque, reflex torque measured at a selected low stretch velocity of 5 deg/sec, the influence of gravity torque and inertial in vertical stretching mode can be minimized. The averaged speed-dependent reflex torque (ASRT), defined as the measured torque deviated from the baseline torque, is used for quantifying the spastic hypertonia. Four subjects having incurred cerebrovascular accident (CVA) are recruited for time-course study in which the measurements are taken at 72 hours, one week, one month, three months, and six months after onset of stroke. During the development of spasticity, the changes of ASRT and velocity sensitivity of ASRT of the involved and the intact elbow joints are discussed.

Value of dermatomal somatosensory evoked potentials in detecting acute nerve root injury: an experimental study with special emphasis on stimulus intensity.

Study Design. Dermatomal somatosensory-evoked potentials (D-SSEPs) in rats were recorded at the spinal level after L2-, L4-, and L5-dermatome stimulation. Pre- and post-transection patterns and rates of change of corresponding nerve roots were compared to determine accuracy. Objective. To investigate characteristics and normal values of D-SSEP elicited from lower limb dermatomes; to determine specificity, sensitivity, and utility of D-SSEP in detecting single-nerve root injury; and to determine optimal stimulation intensity. Summary of Background Data. D-SSEP allows assessment of single nerve root-specific pathways, electrodiagnosis of lumbosacral radiculopathy, and intraoperative neuromonitoring. Unacceptably low sensitivity and specificity make its value suspect. D-SSEP is insufficiently documented. Methods. Eight rats were used to specify a standard D-SSEP waveform and its characteristics, evaluate stimulation sites and strengths, and determine appropriate stimulation and recording techniques. The L4 nerve root was transected in one group of 8 rats and the L5 in another. D-SSEPs were recorded at the thoracolumbar junction following submaximal and supramaximal stimulation at the L2, L4, and L5 dermatomal fields. Potentials recorded before transection, and immediately, 1 hour, and 1 week post-transection were compared. Results. Reproducible spinal responses were obtained in all rats on all tests. Stimulation intensity, but not rates, affected amplitude. Relative amplitude reductions in transected-root D-SSEP were larger using submaximal than supramaximal intensity. D-SSEP elicited by submaximal than supramaximal intensity produced fewer false negatives and false positives. Conclusions. D-SSEP is valuable for detecting acute single nerve root injury. In clinical settings, submaximal dermatomal stimulation identifies conduction abnormalities more consistently and with fewer false negatives and false positives than does supramaximal stimulation. We recommend submaximal stimulation.

Tremor modulation in patients with Parkinson’s disease compared to healthy counterparts during loaded postural holding

Through examining tremor dynamics, the study sought to investigate the effects of load characteristics upon control strategies in patients with Parkinsons disease (PD) during postural holding. Eleven untreated patients and eleven healthy adults conducted a static pointing task with an outstretched arm, with a manipulated load of 100 g on the index finger. Oscillatory activities in the upper limb were contrasted between the unloaded and loaded conditions. The results showed that PD patients demonstrated abnormal modulation of tremor amplitude in the finger, hand, and upper arm in the opposing load condition. When the load was applied, the PD patients presented a nearly opposite pattern of tremor coupling between limb segments, contrary to the normal release and enhancement of tremor coupling in the finger-hand and hand-forearm complexes, respectively. Principal component analysis suggested that normal postural tremors could be explained by a load-dependent component that had high communality with tremors of the distal segments. In contrast, major principal components of PD tremor were invariant to load addition. Multi-segment tremors in PD were atypically organized during loaded postural holding, signifying that coordinative control of the upper limb in the patients was impaired in the absence of exploitation of a germane distal strategy against inertial perturbation.

Application of Atomic Force Microscopy to Investigate Axonal Growth of PC-12 Neuron-like Cells

A nerve conduit with suitable biomechanical and biochemical environment may improve the regeneration of axons of the injured peripheral nerve. The PC-12 cells were cultured in PRMI medium 1640 and then axonal growth was induced by using nerve growth factor. Time-course morphological changes of the cells were analyzed by using an optical microscope. Regional viscoelasticity and adhesion force of axons were measured by an atomic force microscope by using ramp-and-hold indentation and scratching. The data were fitted with a quasi-viscoelastic model by a method developed previously. Morphological results revealed that cell body length and branch number were highly correlated with axonal growth process and average axon length can be used to define the stage of growth process. Electrical field with intensity of 100mV/mm could enhance the growth rate of axons by 2.88 folds. AFM results showed that the mean elastic modulus of axon increased with stage and the growth cone region has higher Young’s modulus than the middle region. Furthermore, the adhesion force on middle region of axon was smaller than that of proximal region and growth cone.

Atypical task-invariant organization of multi-segment tremors in patients with Parkinson's disease during manual tracking.

The objective of the study was to investigate the interplay between involuntary tremulous activities and task performance under volitional control for patients with Parkinsons disease (PD) during position tracking. A volunteer sample of nine untreated patients and nine age-matched healthy subjects participated in this study. They performed a sinusoidal tracking maneuver with a shoulder and a static pointing task; meanwhile, a position trace of the index and accelerometer data in the upper limb were recorded to characterize tracking performance and postural-kinetic tremors. In reference to postural tremor, the kinetic tremor of control subjects during tracking was considerably modulated, leading to a lower regularity and greater spectral deviation. In contrast, patients with PD demonstrated greater postural and kinetic tremors than control subjects, and tremulous movements of the patients were comparatively task-invariant. The prominent coherence peak, which occurred at 8-12 Hz in control subjects, was atypically presented at 5-8 Hz for PD patients with poorer tracking performance. Functionally, congruency of position tracking was related to amplitude of kinetic tremor after subtracting from amplitude of postural tremor. In conclusion, task-dependent organization of tremulous movements was impaired in patients with PD. The inferior tracking performance of the patients correlated implicitly with kinetic tremor, signifying some sharing of neural substrates for manual tracking and tremor generation.