Unconditioned response to electric shock: mechanism in planarians

Some implications of a mathematical theory relating neuronal geometry to the parameters of excitation in unconditioned response of planarians to electric shock are experimentally verified. The regions and patterns of primary neural excitation depend on the relation between the distribution of neural sizes and the wave form of the electric stimulus.     

Optical imaging of a tactile illusion in area 3b of the primary somatosensory cortex

In the tactile funneling illusion, the simultaneous presentation of brief stimuli at multiple points on the skin produces a single focal sensation at the center of the stimulus pattern even when no physical stimulus occurs at that site. Consistent with the funneling percept, we show with optical imaging in area 3b of the primary somatosensory cortex (SI) that simultaneous stimulation of two fingertips produces a single focal cortical activation between the single fingertip activation regions. Thus, in contrast to traditional views of the body map, topographic representation in the SI reflects the perceived rather than the physical location of peripheral stimulation.     

Bottom-up dependent gating of frontal signals in early visual cortex

The frontal eye field (FEF) is one of several cortical regions thought to modulate sensory inputs. Moreover, several hypotheses suggest that the FEF can only modulate early visual areas in the presence of a visual stimulus. To test for bottom-up gating of frontal signals, we microstimulated subregions in the FEF of two monkeys and measured the effects throughout the brain with functional magnetic resonance imaging. The activity of higher-order visual areas was strongly modulated by FEF stimulation, independent of visual stimulation. In contrast, FEF stimulation induced a topographically specific pattern of enhancement and suppression in early visual areas, but only in the presence of a visual stimulus. Modulation strength depended on stimulus contrast and on the presence of distractors. We conclude that bottom-up activation is needed to enable top-down modulation of early visual cortex and that stimulus saliency determines the strength of this modulation.     

Lateralized cognitive processes and lateralized task control in the human brain

The principles underlying human hemispheric specialization are poorly understood. We used functional magnetic resonance imaging of letter and visuospatial decision tasks with identical word stimuli to address two unresolved problems. First, hemispheric specialization depended on the nature of the task rather than on the nature of the stimulus. Second, analysis of frontal candidate regions for cognitive control showed increased coupling between left anterior cingulate cortex (ACC) and left inferior frontal gyrus during letter decisions, whereas right ACC showed enhanced coupling with right parietal areas during visuospatial decisions. Cognitive control is thus localized in the same hemisphere as task execution.     

A cortical region consisting entirely of face-selective cells

Face perception is a skill crucial to primates. In both humans and macaque monkeys, functional magnetic resonance imaging (fMRI) reveals a system of cortical regions that show increased blood flow when the subject views images of faces, compared with images of objects. However, the stimulus selectivity of single neurons within these fMRI-identified regions has not been studied. We used fMRI to identify and target the largest face-selective region in two macaques for single-unit recording. Almost all (97%) of the visually responsive neurons in this region were strongly face selective, indicating that a dedicated cortical area exists to support face processing in the macaque.     

Distributed and overlapping representations of faces and objects in ventral temporal cortex

The functional architecture of the object vision pathway in the human brain was investigated using functional magnetic resonance imaging to measure patterns of response in ventral temporal cortex while subjects viewed faces, cats, five categories of man-made objects, and nonsense pictures. A distinct pattern of response was found for each stimulus category. The distinctiveness of the response to a given category was not due simply to the regions that responded maximally to that category, because the category being viewed also could be identified on the basis of the pattern of response when those regions were excluded from the analysis. Patterns of response that discriminated among all categories were found even within cortical regions that responded maximally to only one category. These results indicate that the representations of faces and objects in ventral temporal cortex are widely distributed and overlapping.     

Illusory correlation of brightness enhancement and transients in the nervous system

Short light flashes can appear brighter than longer flashes. This brightness enhancement has often been attributed to neural transients occurring shortly after stimulus onset. This attribution assumes an equivalence between the totality of the response to a stimulus of a given duration and the instantaneous response at a given time after stimulus onset. Recordings from Limulus photoreceptors indicate that this attribution is an example of illusory correlation.     

Neuroimaging evidence for dissociable forms of repetition priming

Repetition priming has been characterized neurophysiologically as a decreased response following stimulus repetition. The present study used event-related functional magnetic resonance imaging to investigate whether this repetition-related response is sensitive to stimulus familiarity. A right fusiform region exhibited an attenuated response to the repetition of familiar stimuli, both faces and symbols, but exhibited an enhanced response to the repetition of unfamiliar stimuli. Moreover, both repetition effects were modulated by lag between successive presentations. Further experiments replicated the interactions between repetition, familiarity, and lag and demonstrated the persistence of these effects over multiple repetitions. Priming-related responses are therefore not unitary but depend on the presence or absence of preexisting stimulus representations.     

Superstition: a matter of bias, not detectability

Pigeons discriminated between stimulus changes dependent on their pecking and stimulus changes occurring independently of their behavior. Their performance was accurate, and when the payoffs for "hits" and "correct rejections" were varied, their response bias varied in a fashion similar to that of human observers detecting signals in a background of noise.     

Frog retina: detection of movement

The response of class 2 ganglion cells in the frog retina is dependent on the angular velocity of a black visual stimulus whose size (1.20 degrees ) and contrast against a background are held constant. The relation between neuronal discharge rate and the angular velocity of the stimulus may be expressed as a power function.     

Imprinting: lasting effects on uracil incorporation into chick brain

On the first day after hatching, domestic chicks were trained for 20, 60, 120, or 240 minutes with an imprinting stimulus. On the second day, they were all retrained for 60 minutes. The greater the chicks' experience on the first day, the lower the rate of incorporation of tritiated uracil into macromolecules in the anterior part of the forebrain roof on the second day. Such effects were not found in other brain regions, nor in any brain region of chicks that received similar treatment on the first day but were not retrained on the second.     

Echo-ranging neurons in the inferior colliculus of bats

Bats measure the distance to an object in terms of the time lag between their outgoing orientation sounds and the returning echo. For measurement of the time lag, the latency of response of a neuron to a stimulus must be nearly constant regardless of the stimulus amplitude and envelope. Otherwise, a large error would be introduced into the measurement. Bats have neurons that are specialized for echo ranging.     

Entrainment of a population of synthetic genetic oscillators

Biological clocks are self-sustained oscillators that adjust their phase to the daily environmental cycles in a process known as entrainment. Molecular dissection and mathematical modeling of biological oscillators have progressed quite far, but quantitative insights on the entrainment of clocks are relatively sparse. We simultaneously tracked the phases of hundreds of synthetic genetic oscillators relative to a common external stimulus to map the entrainment regions predicted by a detailed model of the clock. Synthetic oscillators were frequency-locked in wide intervals of the external period and showed higher-order resonance. Computational simulations indicated that natural oscillators may contain a positive-feedback loop to robustly adapt to environmental cycles.     

The contribution of single synapses to sensory representation in vivo

The extent to which synaptic activity can signal a sensory stimulus limits the information available to a neuron. We determined the contribution of individual synapses to sensory representation by recording excitatory postsynaptic currents (EPSCs) in cerebellar granule cells during a time-varying, quantifiable vestibular stimulus. Vestibular-sensitive synapses faithfully reported direction and velocity, rather than position or acceleration of whole-body motion, via bidirectional modulation of EPSC frequency. The lack of short-term synaptic dynamics ensured a highly linear relationship between velocity and charge transfer, and as few as 100 synapses provided resolution approaching psychophysical limits. This indicates that highly accurate stimulus representation can be achieved by small networks and even within single neurons.     

Tonotopic organization of the auditory cortex: pitch versus frequency representation

According to the place principles of the classical hearing theory, the physical entity frequency is encoded in the auditory periphery as place information (tonotopic representation), which is decoded in more central parts of the auditory system to form the subjective entity pitch. However, this relation is true only for pure-tone signals (spectral pitch); it can be quite different in the case of complex auditory stimuli (virtual pitch), thus requiring a multistage process for pitch formation. Neuromagnetic measurements showed that the tonotopic organization of the primary auditory cortex reflects the pitch rather than the frequency of the stimulus; that is, the pitch formation process must take place in subcortical regions.     

Flexible control of mutual inhibition: a neural model of two-interval discrimination

Networks adapt to environmental demands by switching between distinct dynamical behaviors. The activity of frontal-lobe neurons during two-interval discrimination tasks is an example of these adaptable dynamics. Subjects first perceive a stimulus, then hold it in working memory, and finally make a decision by comparing it with a second stimulus. We present a simple mutual-inhibition network model that captures all three task phases within a single framework. The model integrates both working memory and decision making because its dynamical properties are easily controlled without changing its connectivity. Mutual inhibition between nonlinear units is a useful design motif for networks that must display multiple behaviors.     

Cerebellar LTD and learning-dependent timing of conditioned eyelid responses

Mammals can be trained to make a conditioned movement at a precise time, which is correlated to the interval between the conditioned stimulus and unconditioned stimulus during the learning. This learning-dependent timing has been shown to depend on an intact cerebellar cortex, but which cellular process is responsible for this form of learning remains to be demonstrated. Here, we show that protein kinase C-dependent long-term depression in Purkinje cells is necessary for learning-dependent timing of Pavlovian-conditioned eyeblink responses.     

水稻OsSsr1基因的生物信息学分析、亚细胞定位及其表达模式

为了探明盐敏感相关基因[OsSsr1（Oryza sativa L.salt-sensitive related gene 1,GenBank登录号为NM₀01065574）]的亚细胞定位及在水稻不同组织和各种逆境胁迫下的表达模式,通过生物信息学手段、洋葱表皮亚细胞定位、RiceXPro数据库和Real-time PCR对其进行研究。序列分析表明OsSsr1的开放阅读框为2 004 bp,编码一个由667个氨基酸组成并含有5个跨膜区的蛋白质,该蛋白质N端含有一个信号肽;其启动子序列包含TGACG-motif、ABRE、TCA-element和W box等多个与逆境相关的顺式作用元件。GFP融合表达显示,OsSSR1蛋白质定位于细胞膜。RiceXPro数据库中数据分析表明,OsSsr1基因在水稻不同发育期的不同组织中均有表达,在叶中的表达量最高,胚中的表达量最低。Real-time PCR结果表明,OsSsr1表达水平受干旱、高温、高盐、低温、机械伤害、稻瘟病菌、MeJA和ABA的诱导上调。这些结果显示,OsSsr1基因可能在水稻胁迫反应中发挥重要作用。     

Classical conditioning of pain-elicited aggression

Unconditioned aggression between paired animals in response to electric shock has been previously demonstrated. In this study, with the use of classical Pavlovian conditioning procedures, aggression was produced between paired rats as a response to a tone stimulus.     

Demonstration of the influence of stimulus and response categories upon difference limens

Representative types of stimulus and response categories were used with the same subjects in determining the difference threshold for visual velocity discrimination. The observed interaction between these variables and difference limens was pronounced.