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A simple model is developed to describe wave phenomena at electrode/electrolyte interfaces. The electrochemical kinetics include a negative faradaic impedance in order to provide the necessary feedback between the interfacial faradaic current and the local currents flowing in the electrolyte solution. The properties of the model are studied under conditions of fixed current or fixed potential, and in the absence or presence of a supporting electrolyte. Depending on the conditions, the model is shown to give rise to front propagation, pulse propagation, wave trains and spiral waves. The relation with the experimentally reported cases of wave propagation at electrode/electrolyte interfaces is discussed to some extent.

The induction time in the electrocrystallization of lead chloride and lead sulphate on a lead amalgam electrode, determined from the observation of the light scattered by the electrode surface, has been treated according to the well known nucleation models. The analysis shows that the atomistic model is more realistic than the classical model. The critical nuclei size ranges between 0 and 1 growth unit.

Three strategies are described for designing electrochemical oscillators involving electrochemical reactions at inert electrodes. The strategies are based on coupling a negative faradaic impedance with mass transport, and it is argued that the dynamic behaviour of all of these systems is expected to be qualitatively similar. The three “recipes” are illustrated by experiments of simple reduction reactions at the hanging mercury drop electrode.

The classical model of Franck and FitzHugh for current oscillations at the active-passive transition in metal electrodissolution is reconsidered without making the assumption of a discontinuous change in the reaction kinetics at the Flade potential. A simple analytical calculation shows that this model cannot support sustained oscillatory behavior. A new model is presented which incorporates the role of the uncompensated ohmic cell resistance and the dissolving metal ions. The bifurcation structure of this model is studied numerically in some detail and regions of bistability, oscillations and complex (chaotic) behavior are identified.

The complex mixed‐mode and chaotic oscillations in the reduction of indium(III) at a hanging mercury drop electrode in thiocyanate solution are studied in experimental detail in the parameter plane. With the aid of a simple model developed previously, we critically discuss the relation of the experimentally observed periodic–chaotic sequences with those predicted by the Shil’nikov theory of homoclinic orbits. It appears helpful to distinguish between two fundamentally different types of mixed‐mode behavior: ‘‘type 1’’ related to the incomplete homoclinic scenarios observed in the present system and its model; ‘‘type 2’’ related more directly to the Shil’nikov behavior and the classical Rossler type of reinjection mechanism. The definitions and properties of both types of mixed‐mode oscillation are worked out in some detail.

In layer IV of the primary visual cortex, in both the macaque monkey and the cat, geniculocortical terminals representing the two eyes are segregated into alternating zones known as ocular dominance bands. Viewed tangentially, in the monkey these bands take the form of a series of branching parallel stripes that run roughly perpendicular to the border of striate cortex. In the cat, the overall ocular dominance pattern consists of irregularly branching, beaded bands that exhibit no predominant orientation. If the striking differences in the appearance of these two patterns reflect important differences in the basic rules governing cortical ocular dominance, then this poses a problem for attempts to formulate general principles of visual cortical organization. However, it has been suggested that the differences in the appearance of the ocular dominance patterns in these two species could result simply from known differences in the boundary conditions of their geniculocortical pathways. This article describes the formulation and testing of a single computational model that accurately predicts the quite dissimilar ocular dominance patterns in cats and monkeys. This model also generalizes to predict the different ocular dominance patterns observed in young and old three-eyed frogs, supporting the notion that the overall pattern of ocular dominance is governed by a common set of rules. The significance of these results is discussed in terms of previous models, which have focused largely on local processes underlying the development of ocular dominance segregation. Although the present model is not a developmental one, it does shed some light on potential mechanisms for establishing retinotopy in striate cortex and on possible developmental relationships between the geniculostriate pathway and intrinsic modularity of the striate cortex.

The caudal medial accessory subdivision of the inferior olive (cMAO) receives information from the hindlimb from both the gracile nucleus and the lumbosacral spinal cord. This study determined which elements in cMAO serve as the postsynaptic targets of the gracile projection and whether these elements also receive input from the lumbosacral spinal cord. Gracile axons were labeled in cats by anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), visualized with tetramethylbenzidine. Convergence of gracile and lumbosacral axons was evaluated by labeling in the same animal, one pathway by WGA-HRP and the other by degeneration. In cMAO, gracile axons synapse with equal probability on dendritic spines and distal dendritic shafts. This termination pattern contrasts markedly with that of other somatosensory inputs to the inferior olive and may account for the greater heterogeneity in responses to somatosensory stimuli displayed by neurons in cMAO. The distal dendritic shafts receiving gracile input were more likely than dendritic spines to receive convergent input from putative inhibitory synapses. The most likely source of these inhibitory synapses is the parasolitary nucleus, a structure that has been shown by others to receive input from the cerebellum. Thus the parasolitary nucleus may serve as an inhibitory relay between the cerebellum and cMAO. The dendritic spines in cMAO that receive input from the gracile nucleus often receive additional input from the lumbosacral spinal cord. This convergence of somatosensory axons on dendritic spines may provide a mechanism through which the unusually complex receptive fields of neurons in cMAO are generated.

The “classical” indium/thiocyanate oscillator is studied in some more detail at the HMDE. Several qualitative dependences are investigated. Multiperiodic “mixed-mode” oscillations and aperiodic oscillations are observed near the system's transition from steady state to oscillatory behaviour. These oscillations are very reminiscent of those observed in other (electro)chemical oscillators, and seem to indicate some kind of common mechanism.

A simple mathematical formalism is considered for the description of spontaneous oscillations in electrochemical systems. Emphasis is on the modelling of “cathodic” oscillators, i.e. those that involve a metal ion reduction which displays a potential-dependent catalysis or inhibition, resulting in a negative (differential) impedance. The model appears to be able to reproduce many of the essential features of the experimental oscillators. Some of the model’s most severe approximations and assumptions are discussed and their possible improvements indicated.

It is shown that, although the current distribution is inhomogeneous, the frequency dependence of the admittance of a smooth electrode partly covered with an electrically insulating layer in a fractal way will behave as if the electrode surface were homogeneous.

Various types of fractal electrode/electrolyte interfaces are investigated in the presence of an electrode reaction, the rate of which is described by the Butler-Volmer equation in a wide range of overpotentials. Applying scaling analysis, an interesting connection between the Tafel current at a fractal electrode, both in the limit of high and small overpotentials on the one hand and the admittance behaviour of the same electrode on the other, reveals itself. In particular, from Tafel plots in the limit of high overpotentials the effective transfer coefficients are seen to be modified by a geometrical factor α which is equal to the exponent appearing in the description of the CPE frequency dependence found in admittance measurements. Furthermore, at small overpotentials the current is shown to contain information on the exchange current density in a way which applies to all electrode geometries which give rise to CPE behaviour, i.e. not specifically to fractal electrodes.

The impedance spectrum of an electrode having only a circular portion of its surface exposed to a semi-infinite electrolyte solution is investigated for cases in which the bare electrode surface is ideally polarized (i.e. only charging current is flowing across the interface) or in which also a slow Faradaic reaction is proceeding. Analytical and numerical results are given and various possibilities for their application are discussed.

STUDY DESIGN Human cadavera morphometric analysis of the iliac columns and biomechanical implant testing of traditional Galveston technique compared to intrailiac instrumentation of the entire iliac column. OBJECTIVES To describe the anatomy of the iliac columns and to evaluate the strength in forward flexion of a large implant spanning the entire column length compared to standard Galveston technique. SUMMARY OF BACKGROUND DATA We have observed substantial and straight columns of bone in the pelvis, connecting the acetabula to the sacrum, which may allow for improved spinopelvic instrumentation. METHODS Twenty adult cadaveric pelves were used. Each specimen was oriented in the computed tomography scanner to obtain a cross-section of the iliac columns, which begin from 2 cm caudal to the posterior iliac spines and end above the acetabula at the anterior inferior iliac spines. Two different instrumentation techniques were used. Standard Galveston pelvic fixation with paired 6.25-mm diameter rods extending 8 cm into the pelvis (Group 1) was compared to paired 8-mm diameter, 15-cm long custom implants, placed within the length of the entire iliac columns and connected to 6.25-mm spinal rods (Group 2). Both constructs had two rigid cross-links connecting the rods. Testing in forward flexion was performed for each construct with the MTS model 881 at 5 N/sec until failure occurred. RESULTS The rectangular shaped iliac columns averaged 15.2 (SD 0.8) cm in length, 2.5 (SD 0.3) cm in width and were consistently straight. The iliac column orientation as viewed in the transverse plane was 22 degrees laterally directed from the midsagittal plane. For the Galveston technique, failure with a flexion force occurred at a mean of 682 (SD 217) N. The iliac column implants failed at a mean of 2153 (SD 1370) N (P < 0.004). CONCLUSION The human adult pelvis has substantial and straight columns of bone extending from 2 cm below the posterior iliac spine, traversing above the sciatic notch, and ending at the anterior iliac spine. The shape resembles a weight-bearing long bone such as the tibia. Analogous to the architectural pylon, in this cadaver model, large implant instrumentation of the entire length of these pelvic columns provides at least three times stronger anchorage for spinal instrumentation compared to standard Galveston technique.

It has been suggested that synchronous activation of cortical loci in the two cerebral hemispheres during development leads to the stabilization of juvenile callosal connections in some areas of the visual cortex. One way in which loci in opposite hemispheres can be synchronously activated is if they receive signals generated by the same stimulus viewed through different eyes. These ideas lead to the prediction that shifts in the cortical representation of the visual field caused by misalignment of the visual axes (strabismus) should change the width of the callosal zone in the striate cortex. We tested this prediction by using quantitative techniques to compare the tangential distribution of callosal neurons in the striate cortex of strabismic cats to that in normally reared cats. Animals were rendered strabismic surgically at 8-10 days of age and were allowed to survive a minimum of 18 weeks, at which time multiple intracortical injections of the tracer horseradish peroxidase (HRP) were used to reveal the distribution of callosally projecting cells in the contralateral striate cortex. HRP-labeled cells were counted in coronal sections, and data from four animals with divergent strabismus (exotropia) and four with convergent strabismus (esotropia) were compared to those from four normally reared animals. Although our data from strabismic cats do not differ markedly from those reported previously, we find that the distribution of callosal cells in the striate cortex of these cats does not differ significantly from that in our normally reared control cats. These results do not bear out the prediction that surgically shifting the visual axes leads to stabilization of juvenile callosal axons in anomalous places within the striate cortex.

The effect of neonatal bilateral enucleation on the overall distribution of callosal connections in striate and extrastriate visual cortex of the cat was studied using tangential sections from the physically unfolded and flattened cortex. Callosal neurons were labeled by administering the anatomical tracer horseradish peroxidase directly to the transected corpus callosum. The pattern of callosal connections in binocularly enucleated cats showed both consistent differences and consistent similarities with the pattern in normal cats. In agreement with previous studies, it was found that callosal labeling at the 17/18 border of enucleated cats was considerably sparser than in normal cats. Moreover, we found that the strip containing the majority of labeled cells at the 17/18 border was narrower than in normal cats. In both normal and enucleated cats, scattered cells were distributed on either side of the 17/18 callosal strip, well into areas 17 and 18. In much of extrastriate cortex, the pattern of callosal connectivity in enucleated cats looked surprisingly normal. Details of the callosal pattern that were consistently found in normal cats could also be recognized in binocularly enucleated cats, such as two to four bridges of labeling spanning areas 18 and 19. Also, four zones that were free of callosal connectivity in area 7, on the banks of the suprasylvian sulcus, and in the posterior suprasylvian sulcus were found in both normal and enucleated cats. Finally, as in normal cats, dense cell labeling occurred on the crown of the suprasylvian gyrus at its posterior end, from which it extended laterally across both banks of the suprasylvian sulcus and into the fundus of this sulcus. The results of this study suggest that, although the stabilization of callosal connections at the 17/18 border region appears to depend on visual input, this input plays a less prominent role in the stabilization of callosal connections in extrastriate visual cortex.

It has been previously reported that neonatal monocular enucleation in rats and hamsters induces the development of an anomalous band of callosal connections in the middle of area 17 (primary visual cortex) in the hemisphere ipsilateral to the remaining eye. In order to determine whether this effect is due to elimination of retinal activity in one eye, we used the anatomical tracer horseradish peroxidase (HRP) to study the pattern of visual callosal connections in rats in which retinal activity had been blocked by intraocular injections of tetrodotoxin during the first two weeks of life. We found that the callosal pattern in the hemisphere ipsilateral to the eye not treated with tetrodotoxin was not distinguishable from the pattern present in normal rats. In particular, we did not observe the anomalous extra band of callosal connections that occurs in area 17 in the hemisphere ipsilateral to the remaining eye in monocularly enucleated rats. These results indicate that blockade of retinal activity in one eye is not sufficient to cause the marked changes in the pattern of visual callosal connections that are induced by neonatal monocular enucleation.