Noise-enhanced temporal association in neural networks

We consider a network of globally coupled neuronal oscillators subject to random force, and investigate numerically dynamic responses to external periodic driving. The order parameter, which measures the overlap between the configuration of the system and embedded patterns, is found to exhibit stochastic resonance behavior, as manifested by the signal-to-noise ratio (SNR). The optimal noise level at which the SNR reaches its maximum is found to depend on the driving frequency. On the other hand, as the randomness in the driving amplitude is increased, the system undergoes a transition from the memory-retrieval state to the mixed-memory one. The noise effects on the temporal-association state in the absence of external periodic driving are also investigated, revealing similar noise-enhanced resonance.

Synchronization on small-world networks

We investigate collective synchronization in a system of coupled oscillators on small-world networks. The order parameters that measure synchronization of phases and frequencies are introduced and analyzed by means of dynamic simulations and finite-size scaling. Phase synchronization is observed to emerge in the presence of even a tiny fraction P of shortcuts and to display saturated behavior for P > or similar to 0.5. This indicates that the same synchronizability as the random network (P=1) can be achieved with relatively small number of shortcuts. The transient behavior of the synchronization, obtained from the measurement of the relaxation time, is also discussed.

Spontaneous phase oscillation induced by inertia and time delay

We consider a system of coupled oscillators with finite inertia and time-delayed interaction, and investigate the interplay between inertia and delay both analytically and numerically. The phase velocity of the system is examined; revealed in numerical simulations is the emergence of spontaneous phase oscillation without external driving, which turns out to be in good agreement with analytical results derived in the strong-coupling limit. Such self-oscillation is found to suppress synchronization, and its frequency is observed to decrease with inertia and delay. We obtain the phase diagram, which displays oscillatory and stationary phases in the appropriate regions of the parameters.

Pyrokinin/PBAN-like peptides in the central nervous system of Drosophila melanogaster

The pyrokinin/pheromone biosynthesis activating neuropeptide (PBAN) family of peptides found in insects is characterized by a 5-amino-acid C-terminal sequence, FXPRLamide. The pentapeptide is the active core required for diverse physiological functions, including stimulation of pheromone biosynthesis in female moths, stimulation of muscle contraction, induction of embryonic diapause in Bombyx mori, and stimulation of melanization in some larval moths. Recently, this family of peptides has been implicated in accelerating the formation of the puparium in a dipteran. Using bioassay and immunocytochemical techniques, we demonstrate the presence of pyrokinin/PBAN-like peptides in the central nervous system of Drosophila melanogaster. Pheromonotropic activity was shown in the moths Helicoverpa zeaand Helicoverpa armigera by using dissected larval nervous systems and adult heads and bodies of D. melanogaster. Polyclonal antisera against the C-terminal ending of PBAN revealed the location of cell bodies and axons in the central nervous systems of larval and adult flies. Immunoreactive material was detected in at least three groups of neurons in the subesophageal ganglion of 3rd instar larvae, pupae, and adults. The ring gland of both larvae and adults contained immunoreactivity. Adult brain-subesophageal ganglion complex possessed additional neurons. The fused ventral ganglia of both larvae and adults contained three pairs of neurons that sent their axons to a neurohemal organ connected to the abdominal nervous system. These results indicate that the D. melanogasternervous system contains pyrokinin/PBAN-like peptides and that these peptides could be released into the hemolymph.

XY model in small-world networks

The phase transition in the XY model on one-dimensional small-world networks is investigated by means of Monte Carlo simulations. It is found that long-range order is present at finite temperatures, even for very small values of the rewiring probability, suggesting a finite-temperature transition for any nonzero rewiring probability. Nature of the phase transition is discussed in comparison with the globally coupled XY model.

Comparison between anisometropic and strabismic amblyopia using functional magnetic resonance imaging

AIMS

To assess calcarine activation with functional magnetic resonance imaging (fMRI) in patients with anisometropic and strabismic amblyopia.

METHODS

14 amblyopes (eight anisometropic and six strabismic) were studied with fMRI using stimuli of checkerboards of various checker sizes and temporal frequencies. While T2* weighted MRI were obtained every 3 seconds for 6 minutes, patients viewed the stimuli monocularly with either the amblyopic or sound eye.

RESULTS

Amblyopic eyes showed reduced calcarine activation compared with contralateral sound eyes in fMRI in all subjects. The calcarine activation from amblyopic eyes in anisometropic amblyopes was more suppressed at higher spatial frequencies, while that from amblyopic eyes in strabismic amblyopes was more suppressed at lower spatial frequencies.

CONCLUSION

These results suggest that fMRI is a useful tool for the study of amblyopia in humans. The calcarine activation via amblyopic eyes because of anisometropia or strabismus has different temporospatial characteristics, which suggests differences in the neurophysiological mechanisms between two types of amblyopia.

The effect of oxygen on retinal degeneration in wild-type and hsp70.1 knockout neonatal retinal degeneration mice

The present study examined the effect of oxygen on photoreceptor degeneration in the retina of heat shock protein 70.1 (hsp70.1) knockout type and wild-type retinal degeneration (rd) mice. All the neonatal rd mice were exposed to hyperoixa for 5 days after birth, and then were returned to room air before being sacrificed. At the postnatal 10, 14, 18, and 21 days, the ratio of outer nuclear layer (ONL) thickness to total retinal thickness was compared between hsp70.1 knockout type and wild type. The retina was also examined for DNA fragmentation by TdT-mediated biotin-dUTP nick-end labeling (TUNEL). In hsp70.1 knockout type, the ratio of ONL to total retinal thickness was higher than that in the wild type at each time. There was the remarkable difference in the number and distribution of TUNEL-positive cells between hsp70.1 knockout type and wild type rd mice. In conclusion, an oxygen-induced modulation of the rate of photoreceptor degeneration was more marked in the hsp70.1 knockout type than wild type rd mice.

Binocularity and spatial frequency dependence of calcarine activation in two types of amblyopia

OBJECTIVE AND BACKGROUND

Strabismus and anisometropia early in life frequently causes monocular amblyopia. Activation of the visual cortex is compared between the two types of amblyopia to elucidate differences in the pathogenetic mechanism of the disease.

METHODS

Using an EPI gradient echo sequence in 1.5T MRI, calcarine activation by monocular viewing of checkerboard patterns with reversal was examined in terms of binocularity of the activation and dependence on the spatial frequency of the stimuli.

RESULTS

First, the proportion of voxels activated by both normal and amblyopic eye monocular stimulations is lower in the strabismic group than in the anisometropic group. Second, the activation by higher-spatial-frequency stimuli is reduced in the anisometropic group, but not in the strabismic group.

CONCLUSIONS

These findings from the human visual cortex are consistent with the view proposed based on animal research that the loss of binocular interaction and the undersampling of high-spatial-frequency components of visual stimuli are each one of the underlying changes in strabismic and anisometropic amblyopia, respectively.

Biocatalysis in ionic liquids: markedly enhanced enantioselectivity of lipase

[reaction: see text] Lipase-catalyzed transesterifications in ionic liquids proceeded with markedly enhanced enantioselectivity. It was observed that lipases were up to 25 times more enantioselective in ionic liquids than in conventional organic solvents.

Effect of ADCON-L on adjustable strabismus surgery in rabbits

BACKGROUND/AIMS

In search of a way to prevent postoperative adhesion after strabismus surgery, an animal study was performed to assess the effect of a gel consisting of a polyglycan ester in a gelatin matrix (ADCON-L).

METHODS

Bilateral recessions of superior rectus muscle (SR) were performed on 16 rabbits. ADCON-L was applied beneath and over the SR in the right eyes of all rabbits, while the operative fields in the left eyes were irrigated with a balanced salt solution (BSS). The adjustment was performed on each SR at 4 and 7 days postoperatively on the same eye. The length and force of the adjustment and the degree of adhesion were recorded. At 3 weeks postoperatively, disinsertional force was measured in several of the eyes, and the other eyes were enucleated.

RESULTS

The length of the adjustment was longer and the force of the adjustment was less in the ADCON-L group than in the BSS treated group at 4 and 7 days postoperatively (p=0.00). A significant reduction (p=0.00) in the degree of adhesion was noted in eyes treated with ADCON-L. There was no significant difference in disinsertional force between the two groups. Histopathological evaluation of the muscle revealed decreased fibrosis of perimuscular connective tissue in eyes treated with ADCON-L at 3 weeks postoperatively.

CONCLUSION

This study suggests that ADCON-L helps to prevent postoperative adhesion in rabbits and enables adjustment twice within 7 days postoperatively without complications.

Efficacy of removal of buckle after scleral buckling surgery for retinopathy of prematurity

BACKGROUND OR PURPOSE: A series of encouraging reports over the past decade indicate that scleral buckling (SB) surgery may lessen or eliminate vitreoretinal traction in advanced retinopathy of prematurity (ROP). The effects of SB surgery on refraction and ocular growth, however, have not been demonstrated. We investigated the effects of postoperative removal of buckle in infants whose retinas were reattached in stage 4 ROP.

METHODS

Selected for study were 6 eyes of 3 patients whose retinas had been reattached by placing an encircling buckle, 2.5 mm in width, around the eye and whose buckles were subsequently removed. Axial lengths and refractive errors were compared before and after removal of the buckles. The patients were examined for at least 3 years after removal.

RESULTS

There was high myopia in all eyes treated for stage 4 ROP with SB. All retinas remained attached after removal of the buckle. Although there was a variable degree of increase in axial length, myopic refractive error tended to decrease after removal of the buckle.

CONCLUSIONS

There was some decrease in degree of myopia without resulting in retinal detachment or continued vitreous traction after buckle removal following SB surgery for ROP.

Phase synchronization and noise-induced resonance in systems of coupled oscillators

We study synchronization and noise-induced resonance phenomena in systems of globally coupled oscillators, each possessing finite inertia. The behavior of the order parameter, which measures the collective synchronization of the system, is investigated as the noise level and the coupling strength are varied, and hysteretic behavior is manifested. The power spectrum of the phase velocity is also examined and the quality factor as well as the response function is obtained to reveal noise-induced resonance behavior.

Intrinsic finite-size effects in the two-dimensional XY model with irrational frustration

This study investigates in detail the finite-size scaling of the two-dimensional irrationally frustrated XY model. By means of Monte Carlo simulations with entropic sampling, we examine the size dependence of the specific heat, and find remarkable deviation from the conventional finite-size scaling theory, which reveals novel intrinsic finite-size effects. Relaxation dynamics of the system is also considered, and, correspondingly, finite-size scaling of the relaxation time is examined, again giving evidence for the intrinsic finite-size effects and suggesting a zero-temperature glass transition.

Effects of scleral buckling of refraction and ocular growth in young rabbits

BACKGROUND

There have been a series of reports indicating that scleral buckling (SB) surgery may induce high myopia in advanced retinopathy of prematurity. The mechanism of SB on refractive change in children, however, is not clearly known. We designed this study to investigate the effects of SB on refractive error and ocular growth in young rabbits and demonstrate their mechanisms.

METHODS

For the study, SB surgery was performed on the right eyes of nine 5-week-old rabbits and 11 8-week old rabbits, with encircling buckle. The left eyes were monitored for control. Spherical equivalent, corneal power, and axial length were measured before SB and postoperatively at 2, 4, and 8 weeks. We compared the experimental group with the control group and analyzed the influence of age at the time of operation.

RESULTS

In the control group of eyes, corneal power decreased, axial length increased, and spherical equivalent developed emmetropization with aging. In all eyes that underwent SB surgery, high myopia developed, with the increase in axial length as a major factor in inducing myopia. These changes were greater in the 5-week-old group than in the 8-week-old group. In the eyes that underwent SB surgery, axial length increased more than the eyes in the control group up to 2 weeks after surgery, but ocular growth was arrested after that time.

CONCLUSIONS

SB in young rabbits effects ocular growth and results in high myopia, and an increase of axial length plays a major role in this mechanism. Also, the difference in the effects of SB according to age at the time of surgery may suggest that SB in premature infants could induce a significant axial myopia and secondary amblyopia.

Optic neuritis after bee sting

The purpose of this report is to document an unusual case of fully recovered vision after optic neuritis caused by bee sting. A 46-year-old man presented with sudden visual loss after being stung by a bee on the left conjunctiva. He developed optic disc swelling and there was a delay in the P100 wave of the pattern visual evoked potential (VEP). The patient received acute treatment, with intravenous methylprednisolone followed by oral prednisolone. Two days later, visual acuity in the left eye was recovered to 20/20 and P100 latency in pattern VEP was also normalized. Furthermore, visual field and color vision tests revealed no remaining abnormalities. This case suggests that early corticosteroid treatment is effective in optic neuritis caused by bee sting.

Long term refractive outcome in eyes of preterm infants with and without retinopathy of prematurity: comparison of keratometric value, axial length, anterior chamber depth, and lens thickness

BACKGROUND/AIMS

A longitudinal study of premature infants was conducted to examine changes in refractive status and their relation with age and factors influencing the occurrence and degree of myopia. Identification of which of the various refractive factors play important parts in relation to myopia in premature infants was attempted.

METHODS

Under observation were 125 eyes in 65 patients who were found to demonstrate no signs of retinopathy of prematurity (ROP) or who had grade I or II ROP without or after cryotherapy. Cycloplegic refractions were conducted at 6 months, 3 years, and 6 years of age; at 6 years of age keratometric values, lens thicknesses, and axial lengths were recorded, and anterior chamber depths also were measured.

RESULTS

Myopia begins to appear at 6 months of age and its severity increases between the ages of 6 months and 3 years. The condition showed no further progress in subjects older than 3 years. Of the 104 eyes with ROP, those eyes with cicatricial retinopathy tended towards myopia and high myopia while there was no difference in the degree of myopia related to whether or not cryotherapy was conducted. At 6 years of age, the premature infants exhibited shallower anterior chambers, thicker lenses, and higher axial lengths when the degree of the myopia was higher. The keratometric values, however, appeared to bear no relation to the degree of the myopia.

CONCLUSION

These results suggest that the occurrence of myopia is related more strongly to whether or not there is cicatricial retinopathy than whether or not there is cryotherapy. Also, the degree of the myopia was found to be related to the depth of the anterior chamber, the thickness of the lens, and the change in axial length but not to keratometric value.

Synchronization in a system of globally coupled oscillators with time delay

We study the synchronization phenomena in a system of globally coupled oscillators with time delay in the coupling. The self-consistency equations for the order parameter are derived, which depend explicitly on the amount of delay. Analysis of these equations reveals that the system in general exhibits discontinuous transitions in addition to the usual continuous transition, between the incoherent state and a multitude of coherent states with different synchronization frequencies. In particular, the phase diagram is obtained on the plane of the coupling strength and the delay time, and ubiquity of multistability as well as suppression of the synchronization frequency is manifested. Numerical simulations are also performed to give consistent results.

Phakomatous choristoma of the eyelid

This article describes the first report of phakomatous choristoma of the eyelid in Korea. A six-month-old boy underwent excision of a congenital inferonasal orbital mass arising from the left lower lid. A dermoid cyst was suspected, however a diagnosis of phakomatous choristoma was made following conventional histology. An immunohistochemical study of this rare benign congenital tumor was conducted. The cuboidal epithelial cells comprising this choristoma showed strongly positive cytoplasmic staining with S-100 protein and vimentin. They also showed focally positive staining with a neuron-specific enolase, while they showed no immunoreactivity to cytokeratin or epithelial membrane antigen. The results of the immunohistochemical study support the conclusion that this tumor is of lenticular anlage origin.

Synchronization and resonance in a driven system of coupled oscillators

We study the noise effects in a driven system of globally coupled oscillators, with particular attention to the interplay between driving and noise. The self-consistency equation for the order parameter, which measures the collective synchronization of the system, is derived; it is found that the total order parameter decreases monotonically with noise, indicating overall suppression of synchronization. Still, for large coupling strengths, there exists an optimal noise level at which the periodic (ac) component of the order parameter reaches its maximum. The response of the phase velocity is also examined and found to display resonance behavior.