共查询到4条相似文献,搜索用时 15 毫秒
1.
A neural model of binocular integration and rivalry based on the coordination of action-potential timing in primary visual cortex 总被引:1,自引:0,他引:1
In normal vision, the inputs from the two eyes are integrated into a single
percept. When dissimilar images are presented to the two eyes, however,
they compete for perceptual dominance, so that one eye's view suppresses
that of the other. Recent evidence suggests that this phenomenon, known as
binocular rivalry, arises through competition between alternative stimulus
interpretations in extrastriate cortex. Because eye-specific information
appears to be lost at this stage, it remains unclear how the stimulus
conditions that yield binocular rivalry are distinguished from those that
produce stable single vision. Using a neural network that models the
mammalian early visual system, I investigate here the hypothesis that
congruent and conflicting stimuli are distinguished by their different
effects on the relative timing of action potentials in primary visual
cortex (V1), where monocular inputs are first combined. In the model,
congruent stimulation of both eyes results in synchronization of discharges
among binocular neurons in V1. By contrast, conflicting stimulation of the
two eyes results in neuronal asynchrony in this area. This asynchrony then
produces rivalrous response suppression at later stages in the visual
pathway. Synchronization of firing in V1, however, prevents such
competition, thereby ensuring non-rivalrous responses. These novel effects
of spike timing on competition emerge naturally from the network dynamics.
The results suggest that input-related differences in relative spike timing
at an early stage of visual processing may play an important part in the
phenomena both of binocular integration and rivalry; furthermore, they
indicate that the temporal patterning of cortical activity may be a
fundamental mechanism of selection among competing stimulus
representations.
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2.
We compare fMRI-BOLD responses in anesthetized cats with local field potentials (LFPs), aggregate high-frequency responses (analog-Mua) and spiking activity recorded in primary and higher visual cortex of alert animals. The similarity of the activations in these electrophysiological signals to those in the BOLD is quantified by counting recording sites where different stimuli elicit the same relative activation as in the imaging experiments. Using artificial stimuli, a comparison of BOLD and LFP strongly depends on the frequency range used. Stimulating with complex or natural stimuli reduces this frequency dependence and yields a good match of LFP and BOLD. In general, this match is best between 20 and 50 Hz. The measures of high-frequency activity behave qualitatively different: the responses of the analog-Mua match those of the LFP; the spiking activity shows a low concordance with the BOLD signal. This dissociation of BOLD and spiking activity is most prominent upon stimulation with natural stimuli. 相似文献
3.
Cells in the dorsal medial superior temporal cortex (MSTd) process optic flow generated by self-motion during visually guided navigation. A neural model shows how interactions between well-known neural mechanisms (log polar cortical magnification, Gaussian motion-sensitive receptive fields, spatial pooling of motion-sensitive signals and subtractive extraretinal eye movement signals) lead to emergent properties that quantitatively simulate neurophysiological data about MSTd cell properties and psychophysical data about human navigation. Model cells match MSTd neuron responses to optic flow stimuli placed in different parts of the visual field, including position invariance, tuning curves, preferred spiral directions, direction reversals, average response curves and preferred locations for stimulus motion centers. The model shows how the preferred motion direction of the most active MSTd cells can explain human judgments of self-motion direction (heading), without using complex heading templates. The model explains when extraretinal eye movement signals are needed for accurate heading perception, and when retinal input is sufficient, and how heading judgments depend on scene layouts and rotation rates. 相似文献
4.
Miyagawa K Kozai Y Ito Y Furuhama T Naruse K Nonaka K Nagai Y Yamato H Kashima I Ohya K Aoki K Mikuni-Takagaki Y 《Journal of bone and mineral metabolism》2011,29(4):422-436
Our goal in this study was to determine to what extent the physiologic consequences of ovariectomy (OVX) in bones are exacerbated by a lack of daily activity such as walking. We forced 14-week-old female rats to be inactive for 15?weeks with a unique experimental system that prevents standing and walking while allowing other movements. Tibiae, femora, and 4th lumbar vertebrae were analyzed by peripheral quantitative computed tomography (pQCT), microfocused X-ray computed tomography (micro-CT), histology, histomorphometry, Raman spectroscopy, and the three-point bending test. Contrary to our expectation, the exacerbation was very much limited to the cancellous bone parameters. Parameters of femur and tibia cortical bone were affected by the forced inactivity but not by OVX: (1) cross-sectional moment of inertia was significantly smaller in Sham-Inactive rat bones than that of their walking counterparts; (2) the number of sclerostin-positive osteocytes per unit cross-sectional area was larger in Sham-Inactive rat bones than in Sham-Walking rat bones; and (3) material properties such as ultimate stress of inactive rat tibia was lower than that of their walking counterparts. Of note, the additive effect of inactivity and OVX was seen only in a few parameters, such as the cancellous bone mineral density of the lumbar vertebrae and the structural parameters of cancellous bone in the lumbar vertebrae/tibiae. It is concluded that the lack of daily activity is detrimental to the strength and quality of cortical bone in the femur and tibia of rats, while lack of estrogen is not. Our inactive rat model, with the older rats, will aid the study of postmenopausal osteoporosis, the etiology of which may be both hormonal and mechanical. 相似文献