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1.
In 7–8 and 9–10-years old children, we studied event-related potentials (ERPs) during paired comparison of non-verbalizable
visuospatial stimuli presented at an interval of 1.5–1.8 s. Age-related differences were found in the involvement of various
cortical areas in the formation and retention of a short-term memory trace of the reference stimulus and during comparison
of the short-term trace with the test stimulus presented. In both age groups, working memory was associated with an elevation
of the amplitude of the sensory-specific N1 component in the visual cortical areas. Age-related differences in the processing of sensory-specific characteristics of
a stimulus were the greatest in the ERPs to the test stimulus: at the age of 9–10, the N1 component amplitude was significantly increased in all caudal leads and, in the occipital and inferior temporal leads, this
component was preceded by P1 component. At this age, we observed the early involvement of the inferior frontal cortex, which was not observed at the
age of seven. The increase in positivity over that area was observed in the interval of 100–200 ms. Substantial differences
between age groups were found in the late ERP component corresponding to cognitive processes. At the age of 7–8, the presentation
of both the reference and test stimuli causes the increase in the amplitude of the slow positive complex (SPC) in the caudal
liads with the maximum enhancement found in the interval of 300–800 ms in the parietal leads. At the age of 9–10, the SPC
increase, much like in adults, was observed in ERP to the test stimulus only. At this age, adult-like specific changes in
the late phases of ERPs were observed in the fronto-central regions at the different stages of working memory. They are the
increases in the negative N400 wave in the ERP to the reference stimulus and the SPC to the test stimulus. These data show that, at the age of 9–10,
the functional organization of working memory of the adult type is formed; however, the extent to which the frontal cortex,
and its dorsal regions in particular, is involved into working memory processes does not meet yet a definitive level. 相似文献
2.
L M Puchinskaia K I Dudaeva 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》1988,38(5):812-820
Amplitude-temporal analysis was carried out of the EP components of the visual and motor areas elicited by neutral (diffuse light) and structural (checker board pattern) stimuli in different situations, defined by instruction. Interserial comparisons showed that at any instruction, the latency of the first EP component of the motor areas is reduced; as a result it can appear here simultaneously with the EP of the visual areas. At the instruction involving the subject in the process of active change of perception, activation of the right hemisphere, including the motor area, is manifest by EP parameters, while the right occipital area is activated in response to the structural stimulus, and the left one--in response to the neutral stimulus. At complication of the stimulus or instruction, the period is prolonged when the latency of EP components of the motor area is shorter than the latency of the isopolar components of the visual area--from 120 to 150 ms in response to the neutral stimuli and the neutral with their counting; from 90 to 150 ms in response to the structural stimuli; from 80 to 210 ms in response to the neutral stimuli with mental representation of the structural one. 相似文献
3.
T. G. Beteleva 《Human physiology》2000,26(3):265-274
Classification of visual patterns, a differentiating sign of which is the position of the longer axis of an oval and the principal
part of the image, was studied. Stimuli were presented at random to the left (LVF) or right (RVF) visual fields in two situations:same (preceding imageS
1 was of the same form and presented to the same visual field as the current imageS
2) anddifferent (S
1 differed fromS
2 by both form and location). Classification ofdifferent images was less effective compared with that ofsame images during stimulation of LVF and showed no dependence on the preceding image during stimulation of RVF. The matching
of event-related potentials (ERP) in response toS
2 and differential curvesS
2−S
1 revealed the processes related to accessing the information on the preceding stimulus and processing of the current stimulus,
which simultaneously occur during the initial 50 ms in both hemispheres and in the 160–180 ms interval in the right hemisphere.
Both processes were more expressed during stimulation of the contralateral visual field. In the 190–310 ms interval, discrimination
of thesame anddifferent images was determined by processing of information about the current stimulus on the basis of the results of the preceding
stage of analysis. This process was more expressed in the occipital, parietal and temporoparietooccipital regions of the right
hemisphere independently of the stimulated visual field. The involvement of frontal regions at this stage of information processing
was observed only at stimulation of RVF. The dependence of differences of ERP to thesame anddifferent images on the stimulated visual field was revealed for the 320–500-ms interval (N
400 and late positive complex) in the occipital regions. 相似文献
4.
Electrophysiological correlates of the perception of emotional stimuli were studied by means of recording the visual evoked
potentials (EP) in 20 derivations (Fz, Cz, Pz, Oz, Fp
1/2,F
3/4,F
7/8,C
3/4,P
3/4,T
3/4,T
5/6, andO
1/2) during the emotional test performance. The performance of a special task by subjects was assessed positively or negatively
(by administering emotionally positive or negative stimuli, respectively). Factor analysis revealed seven factors, which described
the EP component structure. Analysis of variance demonstrated the influence of the emotional stimuli sign on the factorsP
100,P
140,N
160,P
220,P
340, and “slow wave.” Hemispheric difference in reactions to the stimuli of a different emotional sign were recorded. During
presentation of the positive and negative assessments, the amplitudes of the factorsP
100,P
340, and “slow wave” were maximally different in the left hemisphere, while the factorsN
160 andP
220 were maximally different in the right hemisphere. 相似文献
5.
Evoked potentials (EPs) in the parietal and temporal leads were recorded in 14 young subjects in response to successively administered right- and left-side simple visual symbols, squares and circles, during passive viewing and reactions to randomly presented target stimuli. Depending on task conditions and context, the stimuli were divided into four groups: (1) passively perceived stimuli, (2) irrelevant stimuli administered on the side opposite to the target, (3) irrelevant stimuli on the side of the target, and (4) target stimuli. The EPs were averaged over the groups. With an increase in the demands of attention from the first to the fourth groups of stimuli, a linear increase in activation, estimated by the total amplitude of the N1–P3 component, was observed in the parietal leads. The P3b component was mainly responsible for the growth of the EP amplitude. In the temporal leads, the activation was substantially weaker than in the parietal leads and displayed lower between-group differences. The results support the idea that the parietal cortex in humans is of primary importance in tasks involving visual attention and stimuli selection. 相似文献
6.
The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R
Fd (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23–3.45; shade leaves: 2.74–2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44–4.70 in sun leaves and 5.04–5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P
N on a leaf area basis (mean of 9.1–10.1 μmol CO2 m−2 s−1) and Chl basis, which correlated well with the higher values of stomatal conductance G
s (range 105–180 mmol m−2 s−1), as compared to shade leaves (G
s range 25–77 mmol m−2 s−1; P
N: 3.2–3.7 μmol CO2 m−2 s−1). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R
Fd, which possessed higher values in sun leaves (2.8–3.0) as compared to shade leaves (1.4–1.8). In addition, via R
Fd images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the
leaf area, and in general to a higher extent in sun leaves than in shade leaves. 相似文献
7.
M. J. Ferragamo T. Haresign J. A. Simmons 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,182(1):65-79
Neurons in the inferior colliculus (IC) of the awake big brown bat, Eptesicus fuscus, were examined for joint frequency and latency response properties which could register the timing of the bat's frequency-modulated (FM) biosonar echoes. Best frequencies (BFs) range from 10 kHz to 100 kHz with 50% tuning widths mostly
from 1 kHz to 8 kHz. Neurons respond with one discharge per 2-ms tone burst or FM stimulus at a characteristic latency in
the range of 3–45 ms, with latency variability (SD) of 50 μs to 4–6 ms or more. BF distribution is related to biosonar signal
structure. As observed previously, on a linear frequency scale BFs appear biased to lower frequencies, with 20–40 kHz overrepresented.
However, on a hyperbolic frequency (linear period) scale BFs appear more uniformly distributed, with little overrepresentation.
The cumulative proportion of BFs in FM1 and FM2 bands reconstructs a scaled version of the spectrogram of FM broadcasts. Correcting FM latencies for absolute BF latencies
and BF time-in-sweep reveals a subset of IC cells which respond dynamically to the timing of their BFs in FM sweeps. Behaviorally,
Eptesicus perceives echo delay and phase with microsecond or even submicrosecond accuracy and resolution, but even with use of phase-locked
FM and tone-burst stimuli the cell-by-cell precision of IC time-frequency registration seems inadequate by itself to account
for the temporal acuity exhibited by the bat.
Accepted: 21 June 1997 相似文献
8.
Priya R Tadwal VS Roessle MW Gayen S Hunke C Peng WC Torres J Grüber G 《Journal of bioenergetics and biomembranes》2008,40(4):245-255
The first low resolution solution structure of the soluble domain of subunit b (b
22–156) of the Escherichia coli F1FO ATPsynthase was determined from small-angle X-ray scattering data. The dimeric protein has a boomerang-like shape with a
total length of 16.2 ± 0.3 nm. Fluorescence correlation spectroscopy (FCS) shows that the protein binds effectively to the
subunit δ, confirming their described neighborhood. Using the recombinant C-terminal domain (δ91–177) of subunit δ and the C-terminal peptides of subunit b, b
120–140 and b
140–156, FCS titration experiments were performed to assign the segments involved in δ–b assembly. These data identify the very C-terminal tail b
140–156 to interact with δ91–177. The novel 3D structure of this peptide has been determined by NMR spectroscopy. The molecule adopts a stable helix formation
in solution with a flexible tail between amino acid 140 to 145. 相似文献
9.
Anatol Rapoport 《Bulletin of mathematical biology》1950,12(4):327-337
Input-output formulas are derived for a neuron upon which converge single axones of two other neurons, which are subjected
to a Poisson shower, where a number of different assumptions are made concerning the mechanism of inhibition.
In one assumption so-called “bilateral pre-inhibition” is considered. That is to say, both neuronsN
1 andN
2 may exciteN
3, but if the stimulus of one of them follows within a certain interval σ of the other, the second stimulus is not effective.
This model is essentially no different from that involving two excitatory neurons acting upon a neuron having a refractory
period.
Another mechanism considered involves so-called “pre-and-post” inhibition, in which if two stimuli fromN
1 andN
2 fall within σ,both are ineffective. This case being mathematically much more involved than the preceding, an approximation method is used for
deriving the input-output formula.
Previous papers of this series are denoted by I, II, and III in this paper. 相似文献
10.
The visual evoked potentials (EPs) in response to lateralized and central visual symbols under the conditions of involuntary (passive viewing) and selective attention (when one of the symbols was a target and required a rapid and precise motor reaction) are considered. The evoked potentials in the occipital, parietal, and frontal derivations were recorded in 20 healthy subjects. It was shown that the EP during selective attention are most pronounced and more alike in the parietal derivations. A strong positive correlation was revealed between the EP amplitude ([N1–P3] component) and the EP stability (correlation between the repeated EP). The involuntary and voluntary forms of attention supplement each other: the more expressed the involuntary attention (assessed by the [N1–P3] component) the higher the EP to target stimuli during voluntary attention and the shorter the reaction time. It is suggested that the role of visual attention consists in the increase and stabilization of cortical activity (primarily, the parietal regions) engaged in solving a visual task. 相似文献
11.
When a voluntary action is followed by an unexpected stimulus, a late positive potential (LPP) with a posterior scalp distribution
is elicited in a latency range of 500–700 ms. In the present study, we examined what type of mismatch between expectations
and action outcomes was reflected by the LPP. Twelve student volunteers participated in a task simulating choice of TV programs.
After choosing one of three options displayed as a cue stimulus, they viewed a second stimulus (still TV image). To manipulate
the type of expectation, three kinds of cue conditions were used: thumbnail image condition (three small TV images), category
label condition (three words), and no cue condition (three question marks). Over trials, the second stimulus either matched
(p = .80) or mismatched (p = .20) the chosen option. As compared to matched TV images, mismatched TV images elicited a larger LPP (500–700 ms) in the
thumbnail image and category label conditions. In addition, a larger centroparietal P3 (400–450 ms) was elicited to mismatched
TV images in the thumbnail image condition alone. LPP reflects a conceptual mismatch between a category-based expectation
and an ensuing action outcome, whereas P3 reflects a perceptual mismatch between an image-based expectation and an action
outcome. 相似文献
12.
Photosynthetic parameters, growth, and pigment contents were determined during expansion of the fourth leaf of in vitro photoautotrophically cultured Nicotiana tabacum L. plants at three irradiances [photosynthetically active radiation (400–700 nm): low, LI 60 μmol m−2 s−1; middle, MI 180 μmol m−2 s−1; and high, HI 270 μmol m−2 s−1]. During leaf expansion, several symptoms usually accompanying leaf senescence appeared very early in HI and then in MI plants.
Symptoms of senescence in developing leaves were: decreasing chlorophyll (Chl) a+b content and Chl a/b ratio, decreasing both maximum (FV/FM) and actual (ΦPS2) photochemical efficiency of photosystem 2, and increasing non-photochemical quenching. Nevertheless, net photosynthetic
oxygen evolution rate (P
N) did not decrease consistently with decrease in Chl content, but exhibited a typical ontogenetic course with gradual increase.
P
N reached its maximum before full leaf expansion and then tended to decline. Thus excess irradiance during in vitro cultivation did not cause early start of leaf senescence, but impaired photosynthetic performance and Chl content in leaves
and changed their typical ontogenetic course. 相似文献
13.
The photomechanic infrared receptor for the detection of forest fires in the beetle Melanophila acuminata (Coleoptera: Buprestidae) 总被引:1,自引:0,他引:1
H. Schmitz H. Bleckmann 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,182(5):647-657
We recorded from single units of individual sensilla of the thoracic infrared (IR) pit organs of Melanophila acuminata. When the organ was stimulated with a thermal radiator whose emission spectrum was similar to that of a typical forest fire,
units responded phasically with up to seven spikes within 30–40 ms at a radiation power of 24 mW cm−2. In the experiments all wavelengths shorter than 1.6 μm were excluded by a longpass IR filter. Response latencies were about
4 ms and initial impulse frequencies were up to 250 impulses per second (ips). A single spike could be generated even when
stimulus duration was only 2 ms. Reduction of total radiation power from 24 mW cm−2 to 5 mW cm−2 resulted in increased response latencies of 5–6 ms and the occurrence of only two to three spikes. Initial impulse frequencies
decreased to 125 ips. According to our physiological results and calculations, Melanophila should be able to detect a 10-hectare fire from a distance of 12 km. Mechanical stimuli also evoked responses of the IR sensilla.
All present morphological and physiological findings lead to the conclusion that the IR receptors of Melanophila must function by means of a hitherto undescribed photomechanic mechanism.
Accepted: 1 November 1997 相似文献
14.
Two rice chlorophyll (Chl) b-less mutants (VG28-1, VG30-5) and the respective wild type (WT) plant (cv. Zhonghua No. 11) were analyzed for the changes
in Chl fluorescence parameters, xanthophyll cycle pool, and its de-epoxidation state under exposure to strong irradiance,
SI (1 700 μmol m−2 s−1). We also examined alterations in the chloroplast ultrastructure of the mutants induced by methyl viologen (MV) photooxidation.
During HI (0–3.5 h), the photoinactivation of photosystem 2 (PS2) appeared earlier and more severely in Chl b-less mutants than in the WT. The decreases in maximal photochemical efficiency of PS2 in the dark (Fv/Fm), quantum efficiency of PS2 electron transport (ΦPS2), photochemical quenching (qP), as well as rate of photochemistry (Prate), and the increases in de-epoxidation state (DES) and rate of thermal dissipation of excitation energy (Drate) were significantly greater in Chl b-mutants compared with the WT plant. A relatively larger xanthophyll pool and 78–83 % conversion of violaxanthin into antheraxanthin
and zeaxanthin in the mutants after 3.5 h of HI was accompanied with a high ratio of inactive/total PS2 (0.55–0.73) and high
1–qP (0.57–0.68) which showed that the activities of the xanthophyll cycle were probably insufficient to protect the photosynthetic
apparatus against photoinhibition. No apparent difference of chloroplast ultrastructure was found between Chl b-less mutants and WT plants grown under low, LI (180 μmol m−2 s−1) and high, HI (700 μmol m−2 s−1) irradiance. However, swollen chloroplasts and slight dilation of thylakoids occurred in both mutants and the WT grown under
LI followed by MV treatment. These typical symptoms of photooxidative damage were aggravated as plants were exposed to HI.
Distorted and loose scattered thylakoids were observed in particular in the Chl b-less mutants. A greater extent of photoinhibition and photooxidation in these mutants indicated that the susceptibility to
HI and oxidative stresses was enhanced in the photosynthetic apparatus without Chl b most likely as a consequence of a smaller antenna size. 相似文献
15.
Steven Branstetter 《Environmental Biology of Fishes》1987,19(3):161-173
Synopsis The silky shark, Carcharhinus falciformis, and scalloped hammerhead, Sphyrna lewini, represent >80% of the shark by-catch of the winter swordfish/tuna longline fishery of the northwestern Gulf of Mexico. This
catch represents a potential supplemental fishery, yet little is known of the life histories of the two species. This report
relates reproductive biology data to age and growth estimates for 135 C. falciformis and 78 S. lewini. Unlike other regional populations, C. falciformis in the Gulf of Mexico may have a seasonal 12 month gestation period. Males mature at 210–220 cm TL (6–7 yr); females at >225
cm TL (7–9 yr). Application of age at length data for combined sexes produced von Bertalanffy growth model parameter estimates
of L∞ = 291 cm TL, K = 0.153, t0 = −2.2 yr. Adult male S. lewini outnumbered adult females in catches because of differences in the distributions of the sexually segregated population. Males
mature at 180 cm TL (10 yr); females at 250 cm TL (15 yr). von Bertalanffy parameter estimates for combined sexes of this
species were L∞ = 329 cm TL, K = 0.073, to = −2.2 yr. 相似文献
16.
Noise improves transfer of near-threshold, phase-locked activity of the cochlear nerve: evidence for stochastic resonance? 总被引:2,自引:0,他引:2
K. R. Henry 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,184(6):577-584
Stochastic resonance can be described as improved detection of weak periodic stimuli by a dynamic nonlinear system, resulting
from the simultaneous presentation of a restricted dynamic range of low-intensity noise. This property has been reported in
simple physical and biological activities. The present study describes data consistent with the interpretation that stochastic
resonance can be observed in the response of cochlear neurons. These experiments utilized low levels (−5 to 25 dB SPL) of
stimuli and noise (5 to 30 dB SPL). Stimuli consisted of simultaneously presented 8 kHz (F
1) and 8.8 kHz (F
2) tone bursts, which generated an 800 Hz F
2–F
1 cochlear nerve envelope ensemble response in the gerbil. The mean response threshold was approximately −3 dB SPL. Simultaneous
presentation of a low-intensity wideband noise increased the amplitude of this response. This was observed with tonal stimuli
having intensities of 0–5 dB SPL; responses to stimulus levels >10 dB were attenuated by noise. Response amplitude was increased
by noise levels of 10–15 dB; the amplitude was unaffected by lower levels of noise, and decreased in the presence of higher
noise levels. These properties are compatible with those of stochastic resonance.
Accepted: 11 March 1999 相似文献
17.
Effects of zinc (12–180 μM) alone and in mixtures with 12 μM Cd on metal accumulation, dry masses of roots and shoots, root
respiration rate, variable to maximum fluorescence ratio (FV/FM), and content of photosynthetic pigments were studied in hydroponically cultivated chamomile (Matricaria recutita) plants. The content of Zn in roots and shoots increased with the increasing external Zn concentration and its accumulation
in the roots was higher than that in the shoots. While at lower Zn concentrations (12 and 60 μM) the presence of 12 μM Cd
decreased Zn accumulation in the roots, treatment with 120 and 180 μM Zn together with 12 μM Cd caused enhancement of Zn content
in the root. Presence of Zn (12–120 μM) decreased Cd accumulation in roots. On the other hand, Cd content in the shoots of
plants treated with Zn + Cd exceeded that in the plants treated only with 12 μM Cd. Only higher Zn concentrations (120 and
180 μM) and Zn + Cd mixtures negatively influenced dry mass, chlorophyll (Chl) and carotenoid content, FV/FM and root respiration rate. Chl b was reduced to a higher extent than Chl a. 相似文献
18.
A. D. S. Bala T. T. Takahashi 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2000,186(5):425-434
The pupil of an awake, untrained, head-restrained barn owl was found to dilate in response to sounds with a latency of about
25 ms. The magnitude of the dilation scaled with signal-to-noise ratio. The dilation response habituated when a sound was
repeated, but recovered when stimulus frequency or location was changed. The magnitude of the recovered response was related
to the degree to which habituating and novel stimuli differed and was therefore exploited to measure frequency and spatial
discrimination. Frequency discrimination was examined by habituating the response to a reference tone at 3 kHz or 6 kHz and
determining the minimum change in frequency required to induce recovery. We observed frequency discrimination of 125 Hz at
3 kHz and 250 Hz at 6 kHz – values comparable to those reported by others using an operant task. Spatial discrimination was
assessed by habituating the response to a stimulus from one location and determining the minimum horizontal speaker separation
required for recovery. This yielded the first measure of the minimum audible angle in the barn owl: 3° for broadband noise
and 4.5° for narrowband noise. The acoustically evoked pupillary dilation is thus a promising indicator of auditory discrimination
requiring neither training nor aversive stimuli.
Accepted: 28 February 2000 相似文献
19.
Differences in semantic event-related potentials in learning-disabled,normal, and gifted children 总被引:1,自引:0,他引:1
J. F. Lubar Ph.D. C. A. Mann D. M. Gross M. S. Shively 《Applied psychophysiology and biofeedback》1992,17(1):41-57
Cortical event-related potentials (ERP) were recorded over FZ, CZ, and PZ scalp sites in 15 learning-disabled (LD), 14 gifted (G), and 13 normal control (N) children of ages 8–12. The common stimulus consisted of nouns presented 80 percent of the time; the target stimulus of animal names presented 20 per cent of the time. ERPs were averaged over subjects from 180 msec pre-stimulus to 900 msec post-stimulus. Principal components analysis was used to determine if there were amplitude differences at different post-stimulus latencies as a function of condition. Differences in ERP's between groups (LD, gifted, and controls), scalp locations, and common versus target stimuli were analyzed by ANOVAs. P
3
, Late, P
2
, and N
1
components represented by four factors were identified. Significant differences between G and LD and the N and LD groups were found target stimulus at all central locations for the P
3
component. Differences were found centrally between G and LD, G and N, and N and LD groups for the P
2
component centrally. Other differences were found for the N
1
and late components. These differences could be interpreted as a deficit in either attentional mechanisms or information processing for the LD group. 相似文献
20.
Tiecheng Qiao Robert Witkowski Robin Henderson G. McLendon 《Journal of biological inorganic chemistry》1996,1(5):432-438
The kinetics of methemoglobin reduction by cytochrome b
5 has been studied by stopped-flow and saturation transfer NMR. A forward rate constant k
f = 2.44×104 M–1 s–1 and a reverse rate constant k
b = 540 M–1s–1 have been observed at 10 mm, pH 6.20, 25 °C. The ratio k
f/k
b = k
eq = 43.6 is in good agreement with the equilibrium constant calculated from the electrochemical potential between cyt b
5 and methemoglobin. A bimolecular collisional mechanism is proposed for the electron transfer from cyt b
5 to methemoglobin based on the kinetic data analysis. The dependence of the rate constants on ionic strengths supports such
collisional mechanism. It is also found that the reaction rate strongly depends on the conformations of methemoglobin.
Received: 20 February 1996 / Accepted: 4 June 1996 相似文献