PHASIC ANKLE REFLEX IN SPASTICITY AND PARKINSONIAN RIGIDITY

The purpose of the present study was to examine whether increased fusimotor activity prevails in spasticity and Parkinsonian rigidity. Groups of 15 spastics, 15 Parkinsonian rigid patients, and 15 normal subjects were studied by phasic mechanical and electrical stimulation of the ankle reflex. The following three parameters were determined: (1) the stimulus threshold, (2) the stimulus intensity required to elicit a maximal reflex potential, and (3) the maximal amplitude of the reflex response. The effect of the reinforcement manoeuvre on these reflex parameters was also recorded. An experimental selective nerve block was performed in eight spastics, four Parkinsonian patients, and seven normals.—In spasticity all tests showed an increased stretch reflex activity on mechanical but not on electrical stimulation as compared with normals, indicating an increased fusimotor activity of the dynamic sensitive muscle spindles in spasticity. Some, but not all, of the Parkinsonians showed an increase of the mechanically elicited stretch reflex activity.—The effect of the reinforcement procedure was in normals an increase in ankle reflex activity on mechanical but not on electrical stimulation, indicating that the mechanism of the reinforcement is an increased fusimotor drive. In spastics, the manoeuvre added little to the mechanical sensitivity of the reflex, compatible with the assumption that in these patients there already exists an increased fusimotor activity. In Parkinsonians, the reduced, although clear, effect of the reinforcement manoeuvre, compared to normals, is compatible with a moderate increase in fusimotor activity in these patients.—Selective nerve block produced, in all eight spastics, a reduction of the increased ankle reflex activity, without involving the alpha motor or Ia afferent nerve fibres. This result suggests a high fusimotor drive in these patients. A similar but less pronounced effect was obtained in some, but not all Parkinsonian patients and in normal subjects.—The presence also of an increased alpha moto-neurone excitability in spastics emerged from an increased ratio in spastics, compared to normals, of the maximal reflex to the maximal direct muscular response to mixed nerve stimulation.—The myograms did not reveal any significant difference in muscular properties between the three groups.     

CLINICAL METHOD FOR ELECTRICAL AND MECHANICAL RECORDING OF THE MECHANICALLY AND ELECTRICALLY ELICITED ANKLE REFLEX

A method for quantitative evaluation of the ankle stretch reflex in man has been developed. The method includes recording of the mechanical and electrical stimulus intensity and of the electrical and mechanical reflex response. In addition, it offers the possibility of reflex latency recording. The size of the tendon tap was recorded by a reflex hammer incorporating an accelerometer which converts the retardation force, experienced by the hammer head when it strikes the tendon, to an electrical signal. The output signal has a linear relationship with the moment of force imposed upon the tendon-muscle system by the tap and can therefore be used as an indicator of muscle stretch. The strength of the electrical stimulus was estimated in milliamperes by the voltage drop across a serial resistor in the stimulating circuit. The electrical reflex response was recorded by surface electrodes over the triceps surae muscle, and the best recording electrode placement was determined. The reflex contraction was recorded by a general purpose myograph allowing isotonic as well as isometric recordings. The method described is easy to use, is not painful to the patient, and offers considerable precision and accuracy in ankle reflex recording.     

Brief Technical Note: SIMULTANEOUS HOFFMANN REFLEX MEASUREMENTS IN MULTIPLE MUSCLES AROUND THE ANKLE

Measurement of the Hoffmann reflex (H-reflex) provides an estimate of alpha motoneuron activity in the target motoneuron (MN) pool. The H-reflex has been assessed for a wide variety of reasons in neuroscience research. However, the majority of protocols have focused on the assess ment of only one muscle and its corresponding motoneuron pool at any instant. Previously established protocols do not simultaneously assess reflex activity in multiple muscles elicited from a single stimulation. This new protocol allows for assessment of alpha motoneuron activity in three muscles around the ankle joint from a single stimulus to the sciatic nerve. To elicit the responses, the sciatic nerve was stimulated just prior to its bifurcation into the tibial and common peroneal nerves in the popliteal fossa. Electromyographic recording electrodes were placed on the tibialis anterior, peroneal longus, and soleus muscles. The 1-ms square wave pulse was delivered every 15 s during the recruitment curve mapping. The maximum H reflex and M waves were measured in each muscle and their ratios calculated. The measurement of these ratios simultaneously allows for assessment of the cumulative alpha motoneuron activity about the ankle at a given point in time.     

BLINK REFLEX IN HUNTINGTON''S CHOREA AND PARKINSON''S DISEASE

The electrically-evoked late response (R2) of the blink reflex has been determined in 8 well-documented cases of Huntington's chorea and in 19 Parkinsonian patients. The results obtained from the two groups are compared with those from 10 normal subjects. A statistically significant difference of some components of the blink reflex was obtained when the three groups were compared. In both pathological conditions, the habituation index, latency and differential latency can be considered to represent the opposite extremes from the same scale, providing further evidence of the neurophysiological antagonism between the two disease states. The blink reflex pattern in Huntington's chorea probably reflects a diminished brain-stem interneurone basal activity through an over-inhibition of dopaminergic receptors in the striatum. The electrophysiological analysis of the blink reflex in incipient Huntington's chorea can provide an objective diagnostic assessment. It might be an effective method of detection for dopaminergic-activated carriers asking for genetic counseling.