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Although synaptic plasticity in the human cerebral cortex is governed by metaplasticity, whether a similar mechanism operates at brainstem level is unknown. In this study in healthy humans we examined the effects and interactions induced by pairing supraorbital nerve high-frequency electrical stimulation (HFS) protocols on the R2 component of the trigeminal blink reflex [Mao, J.B. & Evinger, C (2001) J Neurosci., 21:RC151(1-4)]. Changes in the R2 component were tested by pairing three different priming stimulation protocols inducing long-term potentiation (LTP)-like or long-term depression (LTD)-like effects (LTP-HFS and LTD-HFS), or no change (CONTROL-HFS) with a subsequent test LTP-HFS. Additionally, to examine changes in the R2 component induced by nonspecific factors, two CONTROL-HFS sessions were paired. Priming LTP-, LTD- or CONTROL-HFS potentiated, inhibited or left unchanged the area of the R2 component. Regardless of the type of priming LTP-, LTD- or CONTROL-HFS, the test LTP-HFS induced negligible differences in the R2 component. When two CONTROL-HFS sessions were paired, the test CONTROL-HFS increased the latency and markedly reduced the duration and area of the R2 component. The analysis of the normalized data across the first three experimental sessions, corrected for the inhibitory effects found in the fourth experiment, showed that the test LTP-HFS potentiated the R2 component area of the trigeminal blink reflex only when preceded by a priming LTD-HFS. We propose that homosynaptic metaplasticity might operate in the brainstem circuitry of the blink reflex.

Theta-burst stimulation (TBS) is currently used for inducing long-lasting changes in primary motor cortex (M1) excitability. More information is needed on how M1 is involved in early motor learning (practice-related improvement in motor performance, motor retention and motor consolidation). We investigated whether inhibitory continuous TBS (cTBS) is an effective experimental approach for modulating early motor learning of a simple finger movement in healthy humans. In a short task, 11 subjects practised 160 movements, and in a longer task also testing motor consolidation ten subjects practised 600 movements. During both experiments subjects randomly received real or sham cTBS over the left M1. Motor evoked potentials were tested at baseline and 7 min after cTBS. In the 160-movement experiment to test motor retention, 20 movements were repeated 30 min after motor practice ended. In the 600-movement experiment motor retention was assessed 15 and 30 min after motor practice ended, motor consolidation was tested by performing 20 movements 24 h after motor practice ended. Kinematic variables - movement amplitude, peak velocity and peak acceleration - were measured. cTBS significantly reduced the practice-related improvement in motor performance of finger movements in the experiment involving 160 movements and in the first part of the experiment involving 600 movements. After cTBS, peak velocity and peak acceleration of the 20 movements testing motor retention decreased whereas those testing motor consolidation remained unchanged. cTBS over M1 degrades practice-related improvement in motor performance and motor retention, but not motor consolidation of a voluntary finger movement.

Many studies have addressed practice effects in motor sequences in Parkinson's disease (PD). Most studied short-term practice and showed that treated patients with mild-to-moderate disease achieve normal or slightly abnormal improvement. Less attention has focused on practice effects after prolonged training (days), and the results are inconclusive. Here, we studied the kinematic changes induced by prolonged practice in a group of medicated patients with mild-to-moderate PD and a healthy control group. We did so by analyzing an internally determined sequential arm movement performed as fast and accurately as possible before and after a 2-week training period. After 1-day's practice, movement duration, pause duration, and movement accuracy improved similarly in patients and controls, indicating that patients benefitted normally from short-term practice. After 1-week's practice, movement and pause duration improved further in both groups, whereas movement accuracy remained unchanged. After 2-weeks' practice, healthy controls continued to improve but patients did not, indicating reduced prolonged practice benefit in PD. Because short-term practice benefit on motor performance is thought to be mediated predominantly by cerebellar activation, whereas long-term practice benefit relies predominantly on the basal ganglia, we attribute our findings to the underlying basal ganglia dysfunction in PD. Our study may be relevant for planning and executing rehabilitation programs in these patients.

We investigated finger movements in patients with hand dystonia to compare the kinematics of repetitive individual and non-individual finger oppositions. We used an optoelectronic motion analysis system to record movements in 3-D space, and recorded three 5-second trials for each task, counting how many finger oppositions subjects carried out during each trial, and measured the duration and amplitude of flexions, extensions, and pauses. During tasks, normal subjects and patients carried out finger flexions faster than extensions, and invariably they paused longer before extension than before flexion. Patients were slower and paused longer than controls during both individual and non-individual oppositions. During individual finger movements, patients were disproportionately slow during extension and pause before extension. Patients with hand dystonia perform finger movements abnormally; they are affected predominantly during individual oppositions. This finding reflects the finer cortical control needed to promote and sustain this highly fractionated type of motor output, and points toward underactivity of the primary motor cortex in dystonia.

By analyzing the kinematics of repetitive, constant-amplitude, finger oppositions, we compared the impairment of individual and nonindividual finger movements in patients with Parkinson's disease. In one task, subjects tapped only the index finger against the thumb (individual oppositions); in the other task, they tapped all four fingers together against the thumb pad (nonindividual oppositions). We used an optoelectronic motion analysis system to record movements in three-dimensional space and recorded three 5-second trials for each task. We counted how many finger oppositions subjects performed during each trial and measured the duration and amplitude of the flexions and extensions. We also calculated the duration of the pauses after flexion and extension. We assessed the deterioration of motor performance in patients by investigating the changes in speed and amplitude with task completion. During both tasks, normal subjects and patients performed finger flexions faster than extensions, and they invariably paused longer after flexion than after extension. Patients performed individual and nonindividual finger movements slowly and with reduced amplitude. Patients were disproportionately slow during flexion and in switching from flexion to extension. Movement slowness increased as finger oppositions progressed but predominantly when patients had to move fingers individually. In conclusion, in patients with Parkinson's disease, the motor performance deteriorated with task completion more during individual than during nonindividual finger movements. Parkinson's disease, therefore, impairs individual finger movements more than gross hand movements. This distinction reflects the finer cortical control needed to promote and sustain this highly fractionated type of motor output.

A retrospective analysis was performed on the records of 33 off-therapy parkinsonian patients. We analyzed the clinical score of three sequential upper limb movements: finger tapping, hand opening and closing, and forearm pronation and supination. The records showed that nearly all patients had difficulty in performing all three motor tasks, but movement scores showed that they found the sequential finger-tapping task significantly more difficult than the other two tasks. We suggest that parkinsonian patients find individual finger movements more difficult to execute than gross hand movements because--owing to their abnormal basal ganglia output--they lack the finer cortical control and greater facilitation that the finger task demands.

We examined the motor performance of Parkinson's disease patients and normal subjects during nonrepetitive and repetitive sequential tasks. Parkinson's disease patients took longer than normal subjects to complete the nonrepetitive task, the sequential drawing of a pentagon. In patients, movement times lengthened as the sequence neared completion. The amount of lengthening was similar in nonrepetitive and repetitive tasks (sequential alternating drawing of each side of the pentagon). In parkinsonian patients the slowing at the end of the sequential tasks does not appear to be influenced by whether the sequential task involves nonrepetitive or repetitive movements.

We compared simultaneous measurement of aortic, direct (Dir) and of indirect (Ind) systolic (S), mean (M) and diastolic (D) arterial pressure (AP) determined by an automatic oscillometric instrument (DINAMAP) in neonates with birthweight of 1000-3680 g. DINAMAP measurements were performed with cuffs of increasing width and length, recommended by the manufacturer for increasing arm circumference, and with a Standard sized cuff (2.5 X 15 cm), previously considered as suitable for neonates of any body size. In addition, we compared simultaneous measurements of Dir SAP and of Ind SAP determined by a Doppler technique and the Standard cuff. In DINAMAP SAP measurements with the Standard cuff, a statistically significant correlation between arm circumference and delta Ind-Dir SAP values (i.e. the difference between simultaneous Ind and Dir SAP measurements) was found. In DINAMAP MAP measurements with the cuff recommended for arm circumference, a statistically significant difference of the mean delta Ind-Dir MAP values was observed in infants whose arm was or was not completely encircled by the bladder of the cuff. In SAP as well as in MAP DINAMAP determinations, the overall error of measurement with the Standard cuff was smaller than with the recommended cuff. The Doppler method was found considerably more accurate than the DINAMAP method for the determination of SAP. In spite of these limitations, the DINAMAP method with the Standard cuff was considered to be reasonably accurate for the clinical determination of SAP and MAP, provided that several consecutive measurements are performed and averaged in order to minimize the error of measurement. When considering DAP measurements the error was so unacceptably high that the DINAMAP method cannot be recommended for clinical use. The need for a careful consideration of the cuff characteristics when evaluating new methods for the indirect measurement of AP in the neonate is emphasized.

Blink and corneal reflexes were studied in 11 patients with Huntington's chorea and the results compared with the severity of the disease. The latency of the R2 component of the blink reflex was delayed and the duration of R2 and of the corneal reflex (CR) prolonged. A greater habituation of the R2 component was found in the patients with involuntary movements in the face, and in some patients a long-lasting depression of R2 was present. A correlation was found between: (a) severity of involuntary face movements and R2 and CR latency and (b) severity of involuntary movements in the neck and latency of R2.