Bilateral interactions in saccade programming

Subjects were required to make a saccade to a target appearing randomly 4° to the left or right of the current fixation position (1280 trials per experiment). Location cues were used to direct visual attention and start saccade preparation to one of the two locations before target onset. When the cue indicated the target location (valid trials), the generation of express saccades (visually guided saccades with latencies around 100 ms) was strongly facilitated. When the opposite location was cued (invalid trials), express saccades were abolished and replaced by a population of mainly fast-regular saccades (latencies around 150 ms). This was found with a peripheral cue independently of whether the fixation point was removed before target onset (gap condition; experiment 1) or remained on throughout the trial (overlap condition; experiment 2). The same pattern also was observed with a central cue that did not involve any visual stimulation at a peripheral location (experiment 3). In the case where the primary saccade was executed in response to the cue and the target appeared at the opposite location, continuous amplitude transition functions were observed: starting at about 60–70 ms from target onset onward, the amplitude of the cue-elicited saccades continuously decreased from 4° to values below 1°. The results are explained by a fixation-gating model, according to which the antagonism between fixation and saccade activity gives rise to multimodal distributions of saccade latencies. It is argued that allocation of visual attention and saccade preparation to one location entails a successive disengagement of the fixation system controlling saccade preparation within the hemifield to which the saccade is prepared and a partial engagement of the opposite fixation system.     

Two sisters with Escobar syndrome

We report on 2 sisters with an autosomal-recessive multiple pterygium syndrome, type Escobar, consisting of multiple pterygia with severe contractures, short stature, and minor facial and external genital anomalies. The striking finding was severe muscular atrophy. We speculate that a neu-romuscular disorder is the underlying pathogenesis of Escobar syndrome. © 1995 Wiley-Liss, Inc.     

Maximal isometric force and neural activity during bilateral and unilateral elbow flexion in humans

We investigated maximal isometric force and electromyographic (EMG) activity of the biceps brachii muscle during rapid bilateral (BL) and unilateral (UL) elbow flexion in 11 right-handed subjects. The BL exhibited a deficit in force for both arms and more so for the right than the left arm during the rising phase of force generation. The EMG of the left biceps brachii muscle was similar during UL and BL, but for the right arm EMG was lower during BL than during UL for the rising phase of force generation. The BL to UL ratio of mean power frequency of the EMG was lower for the right than for the left arm. The data would suggest that the relatively small BL strength was associated with a equally small EMG and a shift to a lower mean power frequency especially for the fast motor units of the dominant muscle.     

Neural mechanisms that contribute to cyclical modulation of the soleus H-reflex in walking in humans

The amplitude of the Hoffmann reflex (H-reflex) of the human soleus muscle is modulated in a cyclical way during walking. This paper addresses two questions associated with the neural mechanisms that might generate this modulation: (1) Does the amplitude of the H-reflex simply rise and fall as a function of the background excitability of the soleus motoneuron pool? (2) Is the modulation of the H-reflex dependent on events associated with activation of the antagonist muscle? The amplitude of the soleus H-reflex was compared under three conditions: natural walking, walking without activating the tibialis anterior muscle, and walking with activation of the soleus muscle in the swing phase. Human subjects were able to perform these three tasks with minimal training. The results indicated that the soleus H-reflex remained very depressed in the swing phase of walking, even when a voluntary contraction of the soleus muscle was superimposed during this time. Moreover, the presence of tibialis anterior activity had a very minor effect on the amplitude of the soleus H-reflex during walking. It is concluded that modulation of the soleus H-reflex is not simply a reflection of the background excitability of the motoneuron pool, and the modulation is not dependent on activation of the antagonist muscle. Other more powerful mechanisms are acting to modulate the reflex, most likely presynaptic inhibition of the primary afferents.     

Further insight into the task-dependent excitability of motor evoked potentials in first dorsal interosseous muscle in humans

We have reexamined the contradictory evidence in which task-dependent excitation of motor evoked potentials (MEPs) in the first dorsal interosseous (FDI) muscle was stronger with increasingly more complex finger tasks than with individual finger movement tasks. In the first step of the experiment, based on previous findings, we investigated remarkable functional differences between intrinsic and extrinsic hand muscles during complex finger tasks (precision and power grip). During the performance of the tasks, the optimal stimulus intensity of the transcranial magnetic stimulation (TMS) was applied to the contralateral motor cortex. MEPs of the FDI, extensor carpi radialis (ECR), and flexor carpi radialis (FCR) muscles were recorded simultaneously with increased background EMG activity step by step in both tasks. The intensity threshold of TMS was lower in the precision grip. Furthermore, the MEP amplitudes of FDI muscle dependent on the background EMG activity were different between these two tasks, i.e., MEP amplitudes and regression coefficients in a precision grip were larger than those in a power grip. Although our results for MEP amplitude and threshold in the FDI muscle were similar to previous reported evidence, the different contributions of a synergistic muscle (in particular, the ECR muscle) during performance in these tasks was new evidence. Since there were no differences in cutaneous afferent effects on both tasks, corticomotoneuronal (CM) cells connected to FDI motoneurons seemed generally to be more active during precision than power gripping, and there were different contributions from synergistic muscles during the performance of these tasks. In the second part of the experiment, the results obtained from the complex tasks were compared with those from a simple task (isolated index finger flexion). MEP amplitudes, dependent on the background EMG activity during isolated index finger flexion, varied among subjects, i.e., the relationship between the MEP amplitude and the background EMG of the FDI muscle showed individual, strategy-dependent modulation. There were several kinds of individual motor strategies for performing the isolated finger movement. The present results may explain the previous contradictory evidence related to the contribution of the CM system during coordinated finger movement.     

Immunohistochemical localization of laminin and type IV collagen in human cutaneous sensory nerve formations

We used immunohistochemical techniques and monoclonal antibodies to localize two basement membrane components (laminin and type IV collagen) in the nerves and sensory nerve formations, or corpuscles, supplying human digital skin. Furthermore, neurofilament proteins, S-100 protein and epithelial membrane antigen were studied in parallel. In dermal nerve trunks, immunostaining for laminin and type IV collagen was found to be co-localized in the perineurium and the Schwann cells, the stronger immunoreactivity being at the external surface of the cells. In the Meissner digital corpuscles, the immunoreactivity for laminin and type IV collagen was mainly observed underlying the cell surface of lamellar cells, while the cytoplasm was weakly immunolabelled or unlabelled. Finally, within Pacinian corpuscles co-localization of the two basement membrane molecules was encountered in the inner core, intermediate layer, outer core and capsule. Laminin and type IV collagen immunoreactivities were also found in blood vessels and sweat glands, apparently labelling basement membrane structures. The present results provide evidence for the presence of basement membrane in all periaxonic cells forming human cutaneous sensory nerve formations, and suggest that all of them are able to synthesize and release some basement membrane components, such as laminin and type IV collagen. The possible role of laminin in sensory nerve formations is discussed.     

Fingertip contact influences human postural control

Touch and pressure stimulation of the body surface can strongly influence apparent body orientation, as well as the maintenance of upright posture during quiet stance. In the present study, we investigated the relationship between postural sway and contact forces at the fingertip while subjects touched a rigid metal bar. Subjects were tested in the tandem Romberg stance with eyes open or closed under three conditions of fingertip contact: no contact, touch contact (<0.98 N of force), and force contact (as much force as desired). Touch contact was as effective as force contact or sight of the surroundings in reducing postural sway when compared to the no contact, eyes closed condition. Body sway and fingertip forces were essentially in phase with force contact, suggesting that fingertip contact forces are physically counteracting body sway. Time delays between body sway and fingertip forces were much larger with light touch contact, suggesting that the fingertip is providing information that allows anticipatory innervation of musculature to reduce body sway. The results are related to observations on precision grip as well as the somatosensory, proprioceptive, and motor mechanisms involved in the reduction of body sway.     

Variability versus heterogeneity in syndromal hypothalamic hamartoblastoma and related disorders: Review and delineation of the Cerebro-Acro-Visceral Early lethality (CAVE) multiplex syndrome

We report on a case of neonatal hypothalamic hamartoblastoma with holoprosencephaly, Hirschsprung disease, and tetramelic postaxial polydactyly. Twenty-seven previous cases of congenital hypothalamic embryonic tumours with associated congenital defects are reviewed. A classification in isolated, associated, and syndromal forms is proposed. The difficulties encountered in differential diagnosis between the syndromal form (mainly represented by the Pallister-Hall syndrome) and related diseases as Smith-Lemli-Opitz type II, holoprosencephaly-polydactyly, orofaciodigital type VI and hydrolethalus syndromes are outlined. Two pathogenic mechanisms are discussed: a classical pleiotropic model and single sequence model. The latter is sufficient to delineate syndromal hypothalamic hamartoblastoma. With the former, syndromal hypothalamic hamartoblastoma cannot be clearly recognized in the absence of a CNS tumour, a child with syndromal hypothalamic hamartoblastoma cannot be reliably diagnosed as Pallister-Hall rather than another MCA syndrome, and, ultimately, the existence of Pallister-Hall syndrome could be questioned, as it could only be the extreme expression of one or several other syndromes. As this hypothesis cannot be proven or disproven at this point, the authors suggest creating the concept of multiplex phenotype. “Cerebro-Acro-Visceral Early lethality multiplex syndrome” is suggested to encompass all the ambiguous cases. Within this complex, an operative classification key is proposed. © 1992 Wiley-Liss, Inc.     

Influence of event anticipation on postural actions accompanying voluntary movement

Summary The central organization of anticipatory postural adjustments was investigated by examining the influence of preparatory set on the temporal relationship between postural and arm (focal) muscle activation. Surface EMG was recorded from the right tibialis anterior, lateral gastrocnemius, anterior deltoid and posterior deltoid muscles when pushing or pulling on a stiff handle. Preparatory set was manipulated by informing the subject of the upcoming direction of responding with a 80, 50 or 20% certainty. This created high, neutral and low levels of preparatory set, respectively. All six subjects showed activation of postural muscles in advance of focal muscles for both push and pull responses. However, only three subjects showed the expected effect of preparatory set on reaction time performance, i.e., an increase of reaction time with decreasing response probability. For these three subjects, the time between the activation of postural and focal muscles was the same for the high and neutral levels of preparatory set, but increased with a low level of preparatory set. The increased postural-focal latency for the low preparatory set condition was due to a longer delay for the activation of the focal muscles but not the postural muscles. This finding suggests that anticipatory postural adjustments and the activation of focal muscles are triggered by separate motor commands.     

Behavioural effects of human fetal dopamine neurons grafted in a rat model of Parkinson's disease

Summary The ventral mesencephalon, containing the developing dopaminergic neurons of the substantia nigra-ventral tegmental region, was obtained from aborted human fetuses of 9–19 weeks of gestation. The tissue was grafted into the striatum of rats previously subjected to a 6-hydroxydopamine lesion of the mesostriatal dopamine pathway. The graft recipients were immunosuppressed by daily injections of Cyclosporin A. Amphetamine-induced motor asymmetry was reduced, and finally totally reversed, only in rats receiving grafts from the 9-week old fetal donor. The fluorescence microscopic analysis revealed large numbers of surviving dopamine neurons, and extensive fiber outgrowth into the host striatum, in these rats. By contrast, rats receiving grafts from 11–19 week old donors had at most only few surviving dopamine neurons. These results indicate that human fetal mesencephalic tissue may be an efficient source of dopamine neurons for functional intracerebral grafting in patients with Parkinson's disease.A preliminary account of some of the results from this study was presented at the New York Academy of Sciences meeting on Cell and tissue transplantation into the adult brain, New York, April 4, 1986