Direction of action is represented in the ventral premotor cortex.

The ventral premotor area (PMv) is a major source of input to the primary motor cortex (M1). To examine the potential hierarchical processing between these motor areas, we recorded the activity of PMv neurons in a monkey trained to perform wrist movements in different directions with the wrist in three different postures. The task dissociated three major variables of wrist movement: muscle activity, direction of joint movement and direction of movement in space. Many PMv neurons were directionally tuned. Nearly all of these neurons (61/65, 94%) were 'extrinsic-like'; they seemed to encode the direction of movement in space independent of forearm posture. These results are strikingly different from results from M1 of the same animal, and suggest that intracortical processing between PMv and M1 may contribute to a sensorimotor transformation between extrinsic and intrinsic coordinate frames.

Thermal myringotomy for eustachian tube dysfunction in hyperbaric oxygen therapy.

Otolaryngologists are frequently asked to manage eustachian tube dysfunction (ETD) in patients undergoing hyperbaric oxygen therapy (HBO). HBO patients with intractable ETD currently are treated by tympanostomy tube placement; typically, these tubes are indwelling far longer than is required by the duration of HBO. Also, tubes in this population are associated with higher complication rates of persistent perforation and otorrhea. We investigated the use of thermal myringotomy as an alternative to tympanostomy tube placement in this clinical setting. Potentially, thermal myringotomy avoids the risks and complications associated with indwelling tympanostomy tubes and would be a temporally more appropriate treatment during short- and intermediate-term HBO. In this study 13 patients undergoing HBO who would have required tympanostomy tube placement instead underwent bilateral thermal myringotomies. At the fifth postoperative week, 96% of myringotomies were patent; this duration is adequate for most HBO courses. No patient required a second myringotomy for premature closure. The persistent perforation rate was 15% (at the end of 6 months), which compares favorably with the rate observed with tympanostomy tubes in this unique population of poor wound healers. Only 1 patient had otorrhea; this resolved with dry ear precautions. This study demonstrates thermal myringotomy to be an effective technique for middle ear ventilation in patients undergoing HBO in whom ETD develops.

Muscle and movement representations in the primary motor cortex.

What aspects of movement are represented in the primary motor cortex (M1): relatively low-level parameters like muscle force, or more abstract parameters like handpath? To examine this issue, the activity of neurons in M1 was recorded in a monkey trained to perform a task that dissociates three major variables of wrist movement: muscle activity, direction of movement at the wrist joint, and direction of movement in space. A substantial group of neurons in M1 (28 out of 88) displayed changes in activity that were muscle-like. Unexpectedly, an even larger group of neurons in M1 (44 out of 88) displayed changes in activity that were related to the direction of wrist movement in space independent of the pattern of muscle activity that generated the movement. Thus, both "muscles" and "movements" appear to be strongly represented in M1.

Congenital anomalies and anthropometry of 42 individuals with deletions of chromosome 18q.

Deletions of chromosome 18q are among the most common segmental aneusomies compatible with life. The estimated frequency is approximately 1/40,000 live births [Cody JD, Pierce JF, Brkanac Z, Plaetke R, Ghidoni PD, Kaye CI, Leach RJ. 1997. Am. J. Med. Genet. 69:280-286]. Most deletions are terminal encompassing as much as 36 Mb, but interstitial deletions have also been reported. We have evaluated 42 subjects with deletions of 18q at our institution. This is the largest number of individuals with this chromosome abnormality studied by one group of investigators. Here we report the physical findings in these individuals. We have compared our findings with those of previously reported cases and have found a significantly different incidence of several minor anomalies in our subjects. We also describe here several anomalies not previously reported in individuals with deletions of 18q, including short frenulum, short palpebral fissures, disproportionate short stature, overlap of second and third toes, and a prominent abdominal venous pattern. Characteristics found in subjects were analyzed for correlation with cytogenetic breakpoints. Several traits were found to correlate with the extent of the deletion. Large deletions were associated with significantly decreased head circumference and ear length as well as the presence of proximally placed and/or anomalous thumbs. Individuals with the smallest deletions were more likely to have metatarsus adductus. Although relatively few genotype/phenotype correlations were apparent, these data demonstrate that correlations with breakpoint are possible. This implies that more correlations will become evident when the more precise molecularly based genotyping is completed. These correlations will identify critical regions on the chromosome in which genes responsible for specific abnormal phenotypes are located.

Step-tracking movements of the wrist. IV. Muscle activity associated with movements in different directions.

We examined the patterns of muscle activity associated with multiple directions of step-tracking movements of the wrist in humans and monkeys. Human subjects made wrist movements to 12 different targets that required varying amounts of flexion-extension and radial-ulnar deviation. Wrist muscles displayed two patterns of electromyographic (EMG) modulation as movement direction changed: amplitude graded and temporally shifted. The amplitude-graded pattern was characterized by modulation of the quantity of muscle activity that occurred during two distinct time periods, an agonist burst interval that began before movement onset and an antagonist burst interval that began just after movement onset. The timing of muscle activity over the two intervals showed little variation with changes in movement direction. For some directions of movement, EMG activity was present over both time intervals, resulting in "double bursts." Modulation of activity during the agonist burst interval was particularly systematic and was well fit by a cosine function. In contrast, the temporally shifted pattern was characterized by a gradual change in the timing of a single burst of muscle activity. The burst occurred at a time intermediate between the agonist and antagonist burst intervals. The temporally shifted pattern was seen less frequently than the amplitude-graded pattern and was present only in selected wrist muscles for specific directions of movement. Monkeys made wrist movements to 8-16 different targets that required varying amounts of flexion-extension and radial-ulnar deviation. These movements were performed more slowly than those of human subjects. The wrist muscles of the monkeys we examined displayed the amplitude-graded pattern of activity but not the temporally shifted pattern. Stimulation of individual wrist muscles in monkeys resulted in wrist movements that were markedly curved, particularly for the wrist extensors. These results indicate that step-tracking movements of the wrist are generated mainly by using the amplitude-graded pattern to modulate muscle activity. We propose that this pattern reflects a central process that decomposes an intended movement into an agonist, "propulsive" component and an antagonist, "braking" component. Separate bursts of muscle activity then are generated to control each component. On the other hand, we argue that the temporally shifted pattern may function to reduce the amount of movement curvature associated with the activation of wrist muscles.

Necrotizing fasciitis of the head and neck: review of the literature and report of a case.

Necrotizing fasciitis is a rapidly spreading, life-threatening, bacterial disease. Mortality rates have been estimated to vary between 8.7% and 74%. Mortality depends on many factors, one of which is early recognition. Necrotizing fasciitis of dental origin has a low prevalence and as such presents diagnostic challenges for the dentist. The literature is reviewed, and a case history is presented.

Common principles underlying the control of rapid, single degree-of-freedom movements at different joints.

Studies of rapid, single degree-of-freedom movements have shown different changes in electromyographic patterns for movement tasks that appear very similar (e.g., movements over different ranges of distance). However, it is not clear whether these differences are a result of joint-specific control schemes or whether they are instead due to the limited range of task parameters studied relative to the mechanical constraints of each joint (e.g., short compared with long movements relative to the range of motion of a particular joint). In this study, we measured and compared the kinematic trajectories and electromyograms recorded during various movement tasks at the wrist, elbow, and ankle. Subjects performed movements over a wide range of distances "as fast as possible," "at a comfortable speed," and against two inertial loads (at the elbow only), and they performed movements over a fixed distance at three different speeds at the wrist and ankle. For fast movements we show that, in spite of some joint-specific differences, the basic pattern of electromyographic (EMG) modulation is similar at all three joints; for example, the agonist EMG burst transitions from a fixed duration to an increasing duration with increasing movement distance at all three joints. Moreover, the distance at which this transition occurs in one joint relative to the distance at which this transition occurs in the other two joints is consistent across subjects. The transition occurs at the shortest distance at the ankle and the longest distance at the wrist. In general we suggest that the data are consistent with a single set of control rules applied at all three joints, with the biomechanical constraints at each joint accounting for the differences in the EMG and kinematic patterns observed across joints.

Co-culture of contiguous developmental fields in a serumless, chemically-defined medium: an in vitro model permissive for coordinate development of the mouse ear.

Pattern formation is intrinsically hierarchical, increasing in complexity from the first early embryonic inductive tissue interactions to the eventual integration of multiple organ systems. Viewed as a problem in pattern formation, the vertebrate ear is an exceedingly complex organ system in which normal morphogenesis requires multiple inductive interactions between a variety of adjacent tissues. In order to model the process of higher level pattern formation, we have developed a method for organ culture of the embryonic murine ear. E10.5 mouse embryos (38 to 42 somite pairs) were microdissected into explants that consist of the first and second branchial arches, the otocyst, and the adjacent neural tube. The growth of these explants in a serumless, chemically-defined medium was compared to medium supplemented with 10% fetal calf serum. After 6 days in culture using serumless medium, we observed that this environment was permissive for the formation of pinnae, rudimentary semicircular canals and cochlear ducts, chondrogenesis of the otic capsule and elongation of the endolymphatic ducts. Posterior elements of Meckel's and Reichert's cartilages were identified as ossicular anlagen. All of these structures maintained appropriate anatomic interrelationships during in vitro development. Furthermore, no significant differences were observed in explants grown in serum-supplemented medium. We conclude that during ear development several histogenetic and morphogenetic processes, including aspects of higher level pattern formation, are mediated primarily by paracrine and/or autocrine factors. The development of an organ culture model using serumless medium should facilitate the discovery of intrinsic factors which regulate the coordinate development of inner, middle and external ear structures.

Effects of a primary motor cortex lesion on step-tracking movements of the wrist.

1. We lesioned the contralateral arm area of the primary motor cortex (M1) in a monkey that had been trained to make rapid step-tracking movements of the wrist in different directions. We examined movement kinematics and electromyographic (EMG) activity of forearm muscles both before and 3.5-5 mo after the lesion. 2. The lesion caused marked changes in movement kinematics and the patterns of activity in agonist, synergist, and antagonist muscles. 3. After the lesion, movements to all targets were performed more slowly. In addition, some movements were misdirected. For example, most movements to the target that required wrist flexion and radial deviation were made in two steps, instead of in a single smooth trajectory. 4. After the lesion, distinct bursts of muscle activity were no longer observed during step-tracking movements. In addition, suppression of antagonist activity at movement onset was abolished or reduced. The relative timing of agonist and synergist muscle activity was markedly altered. 5. We conclude that M1 contributes to the precise spatiotemporal patterning of muscle activity during step-tracking movements.

Preterm premature rupture of membranes: experience with latent periods in excess of seven days.

The purpose of this study was to review the maternal and neonatal outcomes of patients with preterm premature rupture of membranes (PPROM) with a latency period greater than 7 days. Using the perinatal database, there were 11,007 deliveries in a 25-month period, in which 81 patients (0.7%) with singleton pregnancies were admitted with documented PPROM between 20 and 30 weeks' gestation. Twenty-one patients (26%) remained undelivered after 1 week, and 19 of these patients were discharged to outpatient care. Twelve patients (57%) delivered at term and nine patients (43%) delivered prematurely. In the preterm group all reported increased leaking prior to delivery and all neonates had 5-minute Apgar scores higher than 7. Length of stay in the neonatal intensive care unit for all the preterm neonates ranged from 12 to 117 days. The majority of patients with PPROM will deliver within 1 week, but there is a subset of patients with PPROM (one of every seven), characterized by the absence of labor or infection, who may be managed as outpatients and delivered at term.

Differential effects of muscimol microinjection into dorsal and ventral aspects of the premotor cortex of monkeys.

1. A gamma aminobutyric acid (GABAA) receptor agonist, muscimol (Sigma, 5 micrograms/microliters solution), and a GABAB receptor agonist and antagonist, baclofen and phaclofen, respectively, were injected (1.0 microliter) into the dorsal and ventral aspects of the premotor cortex (PM) of two Japanese monkeys (Macaca fuscata), while they were performing a motor task that required wrist flexion or extension to a target. The correct movement was instructed by either 1) a conditional color cue [green or red light emitting diodes (LED)] equidistant from the targets or 2) a directional cue toward extension or flexion (right or left LED). When the green or right LED was illuminated, extension was to be performed. When the red or left LED was illuminated, flexion was required. The movement was triggered by a visual stimulus either simultaneously with the instruction stimulus or after a variable delay. 2. Before drug injection, single-unit recordings were made to select injection sites 1) in the dorsal aspect of the PM (PMd) around the superior precentral sulcus where typical set-related activity was frequently recorded and 2) in the ventral aspect of the PM (PMv) immediately caudal to the genu of the arcuate sulcus where movement-related neurons were densely located. 3. Behavioral deficits were observed primarily at the time muscimol, but not baclofen or phaclofen, was injected. Furthermore, muscimol effects were short-lasting: deficits were most frequently observed during the 10-min injection period but seldom after completion of injection. 4. When muscimol was injected into the PMd, there was an increase in the number of direction errors primarily when the conditional cues were presented. The initiated movements were similar in amplitude and velocity to the preinjection behavior. In contrast, when muscimol was injected into the PMv, many of the initiated movements showed smaller amplitudes and slower velocities, but few direction errors were made. 5. These results suggest that the PMd and PMv play differential roles in motor control: the PMd is more important than PMv in conditional motor behavior and plays a role in the preparation for forthcoming movements. In contrast, the PMv is more specialized for a role in the execution of visually guided movements.

Step-tracking movements of the wrist. III. Influence of changes in load on patterns of muscle activity.

Human subjects performed step-tracking movements of the wrist in the radial direction. Movement amplitude, external load, and accuracy instructions were varied. We used surface electrodes to record muscle activity from an agonist, extensor carpi radialis longus, and an antagonist, extensor carpi ulnaris. When subjects performed movements "as fast as possible" that were opposed by different external loads, we observed two distinct patterns of modulation of the agonist burst. In one pattern, termed pulse-height modulation, the force of the agonist muscle was graded by varying the peak amplitude of a short-duration agonist burst. This pattern occurred when subjects performed movements of different amplitudes with a lightweight manipulandum. In the other pattern, termed pulse-width modulation, the force of the agonist muscle was graded by varying the duration of an agonist burst of nearly maximal amplitude. When the agonist burst was prolonged, the onset of antagonist activity was delayed. This pattern occurred when subjects performed movements of different amplitudes that were opposed by elastic or viscoelastic loads applied to a heavy manipulandum. The strongest subject exhibited more pulse-height modulation and less pulse-width modulation of the agonist burst than other subjects. Conversely, the weakest subject displayed more pulse-width modulation of the agonist burst than other subjects. These observations indicate that the force requirements of a task, relative to the force generating capacity of a subject's agonist muscle(s), have a significant influence on the pattern of agonist modulation. In a second experiment using three nonhuman primates, we observed that agonist bursts in wrist flexor and extensor muscles exhibited strikingly different patterns of modulation. For wrist flexion, agonist bursts in wrist flexors were brief and displayed pulse-height modulation when movement amplitude was varied. For wrist extension, agonist bursts in wrist extensors were prolonged and displayed largely pulse-width modulation when movement amplitude was varied. We suggest that the distinct patterns of modulation observed in the wrist muscles of monkeys were due to differences in the strength of wrist flexors and extensors, rather than to alterations in movement strategy. In a third experiment, we instructed human subjects to be "accurate" when they made step-tracking movements. When subjects performed movements with a lightweight manipulandum, most displayed short-duration agonist bursts that were pulse-height modulated. When subjects performed "accurate" movements that were opposed by elastic loads, they displayed pulse-width modulation of a small-amplitude agonist burst.(ABSTRACT TRUNCATED AT 400 WORDS)

Step-tracking movements of the wrist in humans. II. EMG analysis.

We asked human subjects to make accurate step-tracking movements of the wrist to targets that required 5 degrees-30 degrees of radial or ulnar deviation. Speed instructions were given prior to each trial. Muscle activity was recorded from extensor carpi radialis longus (ECRL) and extensor carpi ulnaris (ECU) using surface electrodes. The agonist muscle initiated each movement with a brief burst of activity which began approximately 45 msec before movement onset. Then, the antagonist muscle displayed a brief burst of activity which began approximately 10 msec after movement onset. The magnitude, but not the timing, of these bursts was modulated by changes in the task requirements. The area of the initial agonist burst varied with changes in both displacement and intended speed. This burst was most highly correlated with the initial peaks of acceleration and jerk. In contrast, the area of the initial antagonist burst varied with changes in intended speed and was less well modulated by changes in displacement. This burst was highly correlated with the reciprocal of movement duration. Some small, fast movements had the same agonist bursts as some large, slow movements. However, the antagonist bursts for these movements differed greatly. This observation provides clear evidence that the magnitudes of the agonist and antagonist bursts are independently controlled. In a prior paper (Hoffman and Strick, 1986b), we proposed that step-tracking movements of different amplitudes and intended speeds are centrally generated by adjusting 2 kinematic variables: (1) the peak value and (2) the duration of a derivative of displacement. The present results suggest that these 2 kinematic parameters are separately generated by independently modulating the magnitudes of the agonist and antagonist bursts. Thus, the peak displacement of a step-tracking movement must be determined by the appropriate adjustment of both bursts of muscle activity.

Orbital cellulitis and orbital fractures.

Orbital cellulitis as a complication of orbital fracture is discussed. Three cases of orbital cellulitis that followed trauma to the orbit are presented. A description of the proposed mechanism by which an orbital fracture predisposes to cellulitis follows. Suggestions are made for prophylactic management.

Step-tracking movements of the wrist in humans. I. Kinematic analysis.

We have examined the kinematics of the initial trajectory of step-tracking movements performed by human subjects. Each subject tracked a target that required 5-30 degrees of radial or ulnar deviation of the wrist. All movements were to be performed as accurately as possible. Speed instructions were given before each trial. When subjects performed different amplitude movements following the same speed instruction, the peaks of velocity, acceleration, and jerk were linearly related to peak displacement. The peaks of velocity, acceleration, and jerk also changed when the speed instruction was altered. Thus, for any given movement, the peak values of the derivatives of displacement were dependent on both movement amplitude and intended speed. As a result, the peak values of the derivatives cannot be used by themselves to control or monitor peak displacement. When subjects performed different amplitude movements following the same speed instruction, movement duration tended to remain constant. In contrast, movement duration changed when the speed instruction was altered. Movements performed when subjects intended to move slowly had longer durations than when subjects intended to move quickly. These results suggest that subjects volitionally alter intended speed by selecting different movement durations. When both movement amplitude and intended speed were varied, the peak displacement of a step-tracking movement was linearly related to the product of 2 kinematic variables: the initial peak of a derivative of displacement (either velocity, acceleration, or jerk) and movement duration. On the basis of our observations, we propose that central commands generate step-tracking movements of different amplitudes and intended speeds by adjusting both the magnitude and duration of a derivative of displacement.

Activity of wrist muscles during step-tracking movements in different directions.

Human subjects made step-tracking movements of the wrist in 12 different directions while electromyographic activity was recorded from the long and short heads of the extensor carpi radialis. Three basic patterns of muscle activity were observed from a single muscle. The agonist pattern consisted of a large burst of activity beginning about 40 ms before movement onset, followed by relative inactivity during the movement. The antagonist pattern consisted of a large burst of activity beginning at or just after movement onset. The third pattern appeared to be a combination of agonist and antagonist patterns in a single muscle. These observations lead us to hypothesize that the nervous system has simplified the task of generating wrist movements in different directions by limiting the patterns of muscle activity to combinations of two basic patterns: agonist and antagonist.