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When vision is blocked in one eye by means of a patch, a small change in saccadic magnitude as well as post saccadic drift develops exclusively in the unseeing eye. Subsequent unpatching restores normal function. Thus the saccadic system is capable of independently adjusting the command to each eye.
Recent in vitro electrophysiological studies have revealed that neighboring interneurons interact with each other in a sub-millisecond time range via gap junctions and that individual dendritic compartments generate local excitation spikes and back-propagated spikes within a single-neuron. However, most in vivo electrophysiological studies using behaving animals only focus on activity rates of single-neurons and/or large neuronal populations without considering the potential role of such sub-millisecond interactions among neurons. This neglect is due to the limitation of ordinary in vivo multi-neuronal recording and spike sorting techniques applied to behaving animals. Though independent component analysis (ICA) is a powerful method to overcome certain limitations, ICA has a serious problem in that the number of single-electrodes (microwires) must be more than the number of single-neurons to be recorded. Our recently-developed method has solved this limitation of ICA, but a few problems have remained: the computational load is heavy, the method can be used only for off-line, not real-time, processing, and the electrode-neuron drift problem remains unsolved. In this paper, solving all these problems, we introduce a novel system consisting of automatic and real-time spike sorting with ICA in combination with a newly developed multi-electrode, dodecatrode. The system has the potential to answer some important neurobiological questions that have not been explored in in vivo electrophysiological experiments: how sub-millisecond interactions between closely neighboring single-neurons act in freely behaving animals. The system promises to be a bridge connecting electrophysiological studies in vitro and in vivo.
This paper reports the first example of electrospray ionization (ESI) for the separation and detection of anions in aqueous solutions by ion mobility spectrometry (IMS). Standard solutions of arsenate, phosphate, sulfate, nitrate, nitrite, chloride, formate, and acetate were analyzed using ESI-IMS and distinct peak patterns and reduced mobility constants (K(0)) were observed for respective anions. Real world water samples were analyzed for nitrate and nitrite to determine the feasibility of using ESI-IMS as a rapid analytical method for monitoring nitrate and nitrite in water systems. The data showed satisfactory correlation between the measured value ([similar]0.16 ppm) and the reported maximum nitrate-nitrogen concentration (0.2 ppm) found in a local drinking water system. For on-site measurement applications, direct sample introduction and air as an alternate drift gas to nitrogen were evaluated. The identities of the nitrite and nitrate mobility peaks were verified by comparison of reduced mobility constants with mass identified nitrate and nitrite ions reported in literature. In the mixing ratio, a linear dynamic range of 3 orders of magnitude and instrument detection limits of 10 ppb for nitrate and 40 ppb for nitrite were obtained. The calibration curves showed r(2) value of 0.98 and slope of 0.06 for nitrate and r(2) value of 0.99 and slope of 0.11 for nitrite.
Borderea chouardii is a relictual and dioecious, strictly sexually reproducing, long-living geophyte of the Dioscoreaceae family. Previous biological and demographic studies have indicated the existence of a uniformly distributed panmictic population of this taxon at the southernmost Spanish pre-Pyrenean mountain ranges where it occurs in rather inaccessible crevices of a single limestone cliff. However, individuals of B. chouardii are spatially subdivided into two subpopulations located, respectively, on the upper and lower parts of the cliff, and vertically separated 150 m. Because of its extreme rarity, B. chouardii was the first Iberian taxon to have a specific conservation plan and has been included in several red lists under the category of critically endangered (CR). However, no previous attempts have been conducted to analyse the fine scale evolutionary mechanisms involved in its present microspatial distribution. Genetic diversity and population structure have been investigated through the analysis of neutral hypervariable markers such as simple sequence repeats (SSRs) and randomly amplified polymorphic DNAs (RAPDs) to unravel the impact of life history traits in the differentiation of the two subpopulations. Both types of molecular markers were unequivocal in distinguishing two genetically distinct groups of individuals corresponding to their spatial separation. However, SSRs detected a higher level of subpopulation differentiation (F(ST) = 0.35, R(ST) = 0.32) than RAPDs (F(ST) = 0.21). SSR data indicated significant deviation from random dispersal of genes and genotypes between the two groups, suggesting that mating occurs mainly among individuals within subpopulations, thus, favouring the divergence between the two groups. This microevolutionary differentiation scenario might have been caused by a coupled effect of past genetic drift and reproductive isolation, as a result of strong glacial age bottlenecks and inefficient dispersal system of pollen and seeds, respectively. The identification of such genetic structure in this narrow endemic prompts a modification of the management strategies of its single extant population.
An inexpensive telemetry system using transducers and recorders commonly available, i.e., Statham and Grass, is described. The direct-current signal of a Statham transducer is applied to a voltage-controlled oscillator, thereby frequency encoding the pressure sensed by the transducer. This encoded signal frequency modulates a Colpitts oscillator, which acts as a radio-frequency oscillator-transmitter in the 88- to 108-MHz band. This transmitter and transducer, along with a rechargeable NiCd battery pack (total wt 0.5 kg), are mounted in a canvas jacket and worn by a dog previously prepared with a chronic indwelling arterial catheter. With a fully charged battery pack, a signal can be transmitted up to 250 ft for 50 h. A frequency-modulation automotive receiver, powered by and interfaced with a Grass 7B recorder, receives the signal and drives a tachometer circuit that reconverts the audio-frequency signal to a voltage proportional to pressure. This voltage is then applied to the driver amplifier of the Grass to produce a charted record. This system introduces no distortion as seen by comparison of direct and telemetered signals and is drift free for intervals exceeding 24 h.
PURPOSE: To compare the orientation column maps elicited by different spatial frequency gratings in cortical area 17 of cats before and during brief elevation of intraocular pressure (IOP). METHODS: IOP was elevated by injecting saline into the anterior chamber of a cat's eye through a syringe needle. The IOP was elevated enough to cause a retinal perfusion pressure (arterial pressure minus IOP) of approximately 30 mm Hg during a brief elevation of IOP. The visual stimulus gratings were varied in spatial frequency, whereas other parameters were kept constant. The orientation column maps of the cortical area 17 were monocularly elicited by drifting gratings of different spatial frequencies and revealed by a brain intrinsic signal optical imaging system. These maps were compared before and during short-term elevation of IOP. RESULTS: The response amplitude of the orientation maps in area 17 decreased during a brief elevation of IOP. This decrease was dependent on the retinal perfusion pressure but not on the absolute IOP. The location of the most visible maps was spatial-frequency dependent. The blurring or loss of the pattern of the orientation maps was most severe when high-spatial-frequency gratings were used and appeared most significantly on the posterior part of the exposed cortex while IOP was elevated. However, the basic patterns of the maps remained unchanged. Changes in cortical signal were not due to changes in the optics of the eye with elevation of IOP. CONCLUSIONS: A stable normal IOP is essential for maintaining normal visual cortical functions. During a brief and high elevation of IOP, the cortical processing of high-spatial-frequency visual information was diminished because of a selectively functional decline of the retinogeniculocortical X pathway by a mechanism of retinal circulation origin.
Localized states embedded in a patterned background are found in numerical simulations of spontaneous pattern formation in a spin-1/2 atomic system with optical feedback. In the vicinity of a parameter region with bistability between two homogeneous states large amplitude peaks as well as dark holes exist as stable localized states on a hexagonal background. Moreover, resonant interaction between oscillatory and stationary inhomogeneous modes produces a nonstationary background which may force the localized states to drift.
A distinctive cerebellar ocular motor disorder, macrosaccadic oscillation, evolved simultaneously with an acute cerebellar syndrome in 4 patients, 2 with haemorrhagic metastatic melanoma deep in the vermis, a third with a presumed cerebellar haematoma and a fourth with focal demyelinating disease. Ocular oscillations were conjugate, horizontal, symmetrical, occurred in bursts of several seconds duration, had amplitudes of 30 degrees to 50 degrees, and were evoked whenever the patient attempted to shift visual fixation or pursue a moving target. Photo-electric recordings in one patient with tumour defined features of this disorder of saccadic eye movement: (i) oscillation was composed of saccades, (ii) frequency was 2 Hz, (iii) bursts occurred with amplitude first increasing and then decreasing, (iv) intervals between beginnings of saccades averaged 260 ms and (v) eye position did not exhibit systematic drift during the intersaccadic period. These features documented the inreased gain and instability of the visually guided saccadic system. By using increased feed-forward gain in a sampled-data control model we simulated the pattern of macrosaccadic oscillation. We belive that the acute loss of the calibrator function of the cerebellum accounts for the gain abnormality underlying macrosaccadic oscillation.
Class I major histocompatibility complex molecules are components of the vertebrate immune system. Polymorphic classical class I molecules determine the specificity of cytolytic T cell and natural killer cell responses and are found in all species. During the timeframe of mammalian evolution, the lifetimes of a functional class I locus are short and those of individual alleles even shorter. In this seminar the role of heterozygote advantage frequency-dependent selection, disease-specific selection and drift in driving this rapid evolution is discussed. The other, non-classical genes, perform other functions within the immune system. They are of more recent invention than the classical class I genes and appear to have evolved from classical class I alleles.
Monitoring of blood pressures is essential to the physiological control of the blood circulatory system when artificial hearts are used. Efforts to obtain long term, reliable direct measurements of blood pressures have not been successful because of blood clotting impairing the function of sensors, baseline drift, artifacts on measurements, and health hazard-related catheterization. This paper is concerned with an on-line estimation technique of blood pressures for a portable artificial heart drive system. The technique is based on measurements made for the drive system outside of the body and on mathematical models of the drive system components. The test of the on-line estimation technique with a mock circulatory loop showed successful correlations between the actual values and their optimal estimates. The developed approach offers the following advantages: elimination of blood clotting problems, accessibility to the pressure transducer for recalibration, and noninvasive location of the transducers.
REASONS FOR PERFORMING STUDY: Vaccination and challenge studies in ponies are the most relevant experimental system for predicting whether strains included in equine influenza vaccines are relevant, but they are difficult to perform. OBJECTIVES: In order to investigate the feasibility of using a small animal model, results of a cross-protection study in hamsters were compared with those from a previous pony challenge experiment. METHODS: Animals were immunised with inactivated vaccines containing one of 4 strains of equine influenza A H3N8 subtype virus isolated over a 26 year period (1963 to 1989), then challenged with a 1989 strain. RESULTS: Although there was no significant difference in titres of excreted virus between groups of vaccinated ponies, hamsters immunised with heterologous strains had significantly higher virus titres in the lung than hamsters vaccinated with the homologous strain. In both ponies and hamsters, the number of animals excreting virus was greater the earlier the isolation date of the vaccine strain, although this was only significant in the hamster study. CONCLUSIONS: Despite differences, the overall conclusion of both the pony and hamster models was that heterologous vaccines may be less effective than homologous vaccines at preventing virus excretion. POTENTIAL RELEVANCE: Further validation is required, but the hamster model shows potential for preliminary assessment of the effects of antigenic drift on vaccine efficacy.
Dynamic overshoot is a small saccade that follows a main saccade, in the opposite direction, with no delay. To re-examine prior reports of dynamic overshoot, the properties of dynamic over-shoot were studied in six normal subjects. The post-saccadic drift of eye movements was studied as well. Horizontal eye movements were recorded with the magnetic-field/search-coil method. System noise level was 0.05 deg. Dynamic overshoot occurred with a frequency of about 13% and was more frequent for saccades 10 deg or less. Its mean size was 0.15 deg and its peak velocity showed it to be saccadic in nature. Binocular recordings for three subjects showed that when dynamic overshoot occurred it was almost always in the abducting eye which also had the least post-saccadic drift. The abducting eye seldom had dynamic overshoot and consistently had a more pronounced post-saccadic drift, almost always in the onward direction. We suggest that, at the end of a saccade, the eye normally is brought to rest by a braking pulse and dynamic overshoot occurs when the braking pulse is accidentally too large. It would appear to serve no useful purpose. Why dynamic overshoot is monocular and coincides with the eye having less post-saccadic drift is unclear.
1. The ability of the central nervous system to compensate for saccadic dysmetria was demonstrated in rhesus monkeys. The behavior of this adaptive mechanism after cerebellar ablations was examined. 2. Monkeys were trained to fixate small target lights. Eye movements were monitored while the animals were seated, with their heads fixed, in a rotating magnetic field. The horizontal recti muscles of one eye were weakened by tenectomy. Saccades made by this weakened eye were hypometric and followed by postsaccadic drift. 3. When the patch was switched so that the weak eye was viewing, the hypometric saccades made by the weak eye gradually became larger, until after 3 days they were essentially orthometric. This indicated that the central nervous system could compensate for a peripheral weakness. 4. The tenectomy operation reduced the strength of the muscles, creating hypometria, and upset the ratio of viscosity to elasticity in the orbit, creating postsaccadic drift in the weak eye. The innervation required to make a saccade has both phasic and tonic components, the so-called pulse and step. The sacccadic repair mechanism increased both the pulse and the step to compensate for the hypometria and also adjusted the ratio of the pulse to the step to eliminate postsaccadic drift. 5. Total cerebellectomies were performed on two monkeys, each of which had one tenectomized eye. These ablations created an enduring saccadic hypermetria and postsaccadic drift in the unoperated eye of both animals. The total cerebellectomy abolished all adaptive repair of the saccadic system. 6. Partial cerebellectomies were performed on two monkeys, each of which had one tenectomized eye. Lesions of the vermis and paravermis (lobes IV-IX) and the fastigial nuclei created an enduring saccadic hypermetria without postsaccadic drift in the unoperated eye of both animals. These lesions abolished adaptive control of the pulse of innervation. Adaptive changes in the step of innervation still occurred, so that postsaccadic drift was always eliminated in the experienced, viewing eye. Thus the midline cerebellum (vermis, paravermis, and fastigial nuclei) appears to be important for repair of saccadic dysmetria, but not for repair of postsaccadic drift. Additional evidence that postsaccadic retinal slip cannot be compensated for in flocculectomized monkeys suggest that the adaptive control of the step may depend on the flocculus. 7. After cerebellar lesions the monkeys were able to make saccades of all amplitudes and directions. The principal deficit in these animals seemed to be that the pulse and step of innervation were no longer appropriate to the target displacement. We conclude that the cerebellum's principal contribution to saccadic eye movements is the adjustment of the gains of the pulse- and step-generating mechanisms. Hence this study supports the hypothesis that repair of dysmetria is a general function of the cerebellum.
Until recently, memory consolidation and storage had been traditionally viewed as a permissive process derived from learning-activated molecular signaling cascades which include activations of the NMDA receptors, CaMKII, PKC, PKA and other kinases, new protein synthesis and CREB-mediated gene expression, and subsequent structural modifications at certain synapses. However, the time-scale of such a cascade is incompatible with the timescale of systems-level memory consolidation. Furthermore, increasing evidence suggests that synaptic proteins and structures are not stationary, but rather are highly dynamical and subjected to metabolic turnovers which would cause drift in synaptic efficacy and subsequently unstable neural circuits. Recent experiments using inducible gene- or protein-knockout techniques reveal that post-learning NMDA receptor and CaMKII reactivations are required for the systems-level consolidation of both hippocampal-dependent and hippocampal-independent memories. Furthermore, the reactivations of the NMDA receptors are also necessary for the long-term storage of old memories in the neural circuits. Therefore, the NMDA receptor reactivation-mediated synaptic reentry reinforcement (SRR) process may represent the unifying cellular mechanism in linking the consolidation and storage of long-term memories from the molecular level to the systems-level.
An off-line data processing system based on a Hewlett Packard 2K programmable calculator to be used with a biochemistry profiling system is described. The program is in two sections. A Data Acquisition phase calculates results from Auto Analyser II peak heights after corrections for drift and stores them on magnetic tape cassettes. Quality control statistics are produced. A Reporting phase types the profile results on self-adhesive pre-printed labels to be attached to the test-request form and also prepares a laboratory record sheet. The system is routinely used to process up to 2000 peak heights per day. Non-profile heights may also be read using this program.
The effect of motion sharpening upon blur discrimination thresholds was examined for a range of speeds and blur widths. Blur discrimination thresholds were measured for drifting edges whose blur was either physically or perceptually constant. Under conditions where edges were kept at a constant physical blur width, discrimination thresholds rose as a function of speed as previously reported. However, when the perceived blur of edges was held constant, discrimination performance was more-or-less constant for speeds up to at least 6.3 deg sec-1. The results indicate that the deterioration of blur discrimination performance with speed may be due to motion sharpening and not motion blur as has previously been suggested. The results are discussed in terms of a scheme whereby a non-linearity in motion processing serves to sharpen moving edges, whilst the finite integration time of the system tends to smear them.
Although child abuse occurs in Nigeria, it has received little attention. This is probably due to the emphasis placed on the more prevalent childhood problems of malnutrition and infection. Another possible reason is the general assumption that in every African society the extended family system always provides love, care and protection to all children. Yet there are traditional child rearing practices which adversely affect some children, such as purposeful neglect or abandonment of severely handicapped children, and twins or triplets in some rural areas. With the alteration of society by rapid socioeconomic and political changes, various forms of child abuse have been identified, particularly in the urban areas. These may be considered the outcome of abnormal interactions of the child, parents/ guardians and society. They include abandonment of normal infants by unmarried or very poor mothers in cities, increased child labour and exploitation of children from rural areas in urban elite families, and abuse of children in urban nuclear families by childminders . Preventive measures include provision of infrastructural facilities and employment opportunities in the rural areas in order to prevent drift of the young population to the cities. This would sustain the supportive role of the extended family system which is rapidly being eroded. There is need for more effective legal protection for the handicapped child, and greater awareness of the existence of child abuse in the community by health and social workers.
Continuously, moving objects under continuous illumination can be seen to move in a direction opposite to their actual motion. This illusory reversed motion can be explained as due to discrete temporal sampling of the moving stimulus by the visual system. If temporal sampling lies behind the illusory motion, then the probability of illusory motion should depend on the temporal frequency of the motion stimulus. By presenting contracting bull's-eye gratings of various spatial frequencies we were able to tease apart the drift speed and temporal frequency. The prevalence of illusory percepts depended on the temporal frequency, not the speed. The data suggest that the human visual system samples the incoming stimulation at a rate near 16 Hz.