An active role of inferior frontal cortex in conscious experience

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Neural networks with constrained inputs as models for pattern formation in primate visual cortex

We present a neural network model for the formation of ocular dominance stripes on primate visual cortex and examine the generic phase behavior and dynamics of the model. The dynamical equation of ocular dominance development can be identified with a class of Langevin equations with a nonconserved order parameter. We first set up and examine an Ising model with long-range interactions in an external field, which is equivalent to the model described by the Langevin equation. We use both mean-field theory and Monte-Carlo simulations to study the equilibrium phase diagram of this equivalent Ising model. The phase diagram comprises three phases: a striped phase, a hexagonal bubble phase, and a uniform paramagnetic phase. We then examine the dynamics of the striped phase by solving the Langevin equation both numerically and by singular perturbation theory. Finally, we compare the results of the model with physiological data. The typical striped structure of the ocular dominance columns corresponds to the zero-field configurations of the model. Monocular deprivation can be simulated by allowing the system to evolve in the absence of an external field at early times and then continuing the simulation in the presence of an external field. The physical and physiological applications of our model are discussed in the conclusion.     

How laboratory-raised Japanese monkeys (Macaca fuscata) perceive rotated photographs of monkeys: Evidence for an inversion effect in face perception

Five laboratory-raised Japanese monkeys (Macaca fuscata) were presented various types of photographs of Japanese and rhesus monkeys (Macaca mulatta) in upright, horizontal, and inverted orientations in a sensory-reinforcement experiment. The ratio of the duration of potential viewing time for the photographs which the subjects controlled to the interval between subject-controlled presentations of them (the D/I score) was used as a measure of preference for the photographs. When inverted photographs were presented, the D/I scores were lower than for upright photographs. The difference in D/I scores between photographs of the two species, which indicated discriminability between them, also diminished when the photographs were inverted. The results obtained suggest an inversion effect in face perception in macaque monkeys.     

Representational geometry of perceptual decisions in the monkey parietal cortex

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Neural network model of the primary visual cortex: From functional architecture to lateral connectivity and back

The role of intrinsic cortical dynamics is a debatable issue. A recent optical imaging study (Kenet et al., 2003) found that activity patterns similar to orientation maps (OMs), emerge in the primary visual cortex (V1) even in the absence of sensory input, suggesting an intrinsic mechanism of OM activation. To better understand these results and shed light on the intrinsic V1 processing, we suggest a neural network model in which OMs are encoded by the intrinsic lateral connections. The proposed connectivity pattern depends on the preferred orientation and, unlike previous models, on the degree of orientation selectivity of the interconnected neurons. We prove that the network has a ring attractor composed of an approximated version of the OMs. Consequently, OMs emerge spontaneously when the network is presented with an unstructured noisy input. Simulations show that the model can be applied to experimental data and generate realistic OMs. We study a variation of the model with spatially restricted connections, and show that it gives rise to states composed of several OMs. We hypothesize that these states can represent local properties of the visual scene. Action Editor: Jonathan D. Victor     

Learning-induced dynamic receptive field changes in primary auditory cortex of the unanaesthetized Mongolian gerbil

Learning-induced changes of the spectro-temporal characteristics of primary auditory cortex (AI) units were studied by response plane analysis of recordings from the AI in unanaesthetized Mongolian gerbils. Using response planes obtained prior to and after auditory discrimination training bins of significant change were identified and their spectro-temporal distribution was studied. Bins of significant changes were generally found to be distributed over the entire spectro-temporal receptive field but occurred most frequently within the first 100 ms of response in the spectral neighbourhood (1.5 octaves) of the frequency of the reinforced conditioned stimulus. Training-induced response decreases occurred early after 10 ms for reinforced conditioned tones and tones in the frequency neighbourhood. Response increases occurred so early only for non-reinforced tones in the neighbourhood of the reinforced frequency and occurred later (after 40 ms) for the reinforced tones. The results are discussed in the light of dynamic disinhibition. Accepted: 13 August 1997     

Field-specific responses in the auditory cortex of the unanaesthetized Mongolian gerbil to tones and slow frequency modulations

Responses of multi-units in the auditory cortex (AC) of unanaesthetized Mongolian gerbils to pure tones and to linearly frequency modulated (FM) sounds were analysed. Three types of responses to pure tones could be clearly distinguished on the basis of spectral tuning properties, response latencies and overall temporal response pattern. In response to FM sweeps these three types discharged in a temporal pattern similar to tone responses. However, for all type-1 units the latencies of some phasic response components shifted systematically as a function of range and/or speed of modulation. Measurements of response latencies to FMs revealed that such responses were evoked whenever the modulation reached a particular instantaneous frequency (F_i). Effective F_i was: (1) independent of modulation range and speed, (2) always reached before the modulation arrived at a local maximum of the frequency response function (FRF) and consequently differed for downward and upward sweeps, and (3) was correlated with the steepest slope of that FRF maximum. The three different types of units were found in discrete and separate fields or regions of the AC. It is concluded that gross temporal response properties are one of the key features distinguishing auditory cortical regions in the Mongolian gerbil. Accepted: 13 August 1997     

M-channels modulate the intrinsic excitability and synaptic responses of layer 2/3 pyramidal neurons in auditory cortex

Neurons in the auditory cortex are believed to utilize temporal patterns of neural activity to accurately process auditory information but the intrinsic neuronal mechanism underlying the control of auditory neural activity is not known. The slowly activating, persistent K⁺ channel, also called M-channel that belongs to the Kv7 family, is already known to be important in regulating subthreshold neural excitability and synaptic summation in neocortical and hippocampal pyramidal neurons. However, its functional role in the primary auditory cortex (A1) has never been characterized. In this study, we investigated the roles of M-channels on neuronal excitability, short-term plasticity, and synaptic summation of A1 layer 2/3 regular spiking pyramidal neurons with whole-cell current-clamp recordings in vitro. We found that blocking M-channels with a selective M-channel blocker, XE991, significantly increased neural excitability of A1 layer 2/3 pyramidal neurons. Furthermore, M-channels controled synaptic responses of intralaminar-evoked excitatory postsynaptic potentials (EPSPs); XE991 significantly increased EPSP amplitude, decreased the rate of short-term depression, and increased the synaptic summation. These results suggest that M-channels are involved in controlling spike output patterns and synaptic responses of A1 layer 2/3 pyramidal neurons, which would have important implications in auditory information processing.     

Adaptive radiation of photosynthetic physiology in the Hawaiian lobeliads: dynamic photosynthetic responses

Hawaiian lobeliads have radiated into habitats from open alpine bogs to densely shaded rainforest interiors, and show corresponding adaptations in steady-state photosynthetic light responses and associated leaf traits. Shaded environments are not uniformly dark, however, but punctuated by sunflecks that carry most of the photosynthetically active light that strikes plants. We asked whether lobeliads have diversified in their dynamic photosynthetic light responses and how dynamic responses influence daily leaf carbon gain. We quantified gas exchange and dynamic light regimes under field conditions for ten species representing each major Hawaiian sublineage. Species in shadier habitats experienced shorter and less numerous sunflecks: average sunfleck length varied from 1.4 ± 1.7 min for Cyanea floribunda in shaded forest understories to 31.2 ± 2.1 min for Trematolobelia kauaiensis on open ridges. As expected, the rate of photosynthetic induction increased significantly toward shadier sites, with assimilation after 60 s rising from ca. 30% of fully induced rates in species from open environments to 60% in those from densely shaded habitats. Uninduced light use efficiency—actual photosynthesis versus that expected under steady-state conditions—increased from 10 to 70% across the same gradient. In silico transplants—modeling daily carbon gain using one species’ photosynthetic light response in its own and other species’ dynamic light regimes—demonstrated the potential adaptive nature of species differences: understory Cyanea pilosa in its light regimes outperformed gap-dwelling Clermontia parviflora, while Clermontia in its light regimes outperformed Cyanea. The apparent crossover in daily photosynthesis occurred at about the same photon flux density where dominance shifts from Cyanea to Clermontia in the field. Our results further support our hypothesis that the lobeliads have diversified physiologically across light environments in Hawaiian ecosystems and that those shifts appear to maximize the carbon gain of each species in its own environment. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Processing of spectral localization-informative changes in sound signals by neurons of inferior colliculus and auditory cortex of the house mouse Mus musculus

Comparative analysis was performed of sensitivity of three populations of neurons of the inferior colliculus central nucleus and of neurons of the auditory cortex A1 and AAF fields of the house mouse Mus musculus to series of signals of wideband noise with spectral notch shifting along the frequency axis and to series of the band noise signals with shifting band. Sensitivity to spectral notches in noise was estimated from a change of impulse activity depending on notch location on the frequency axis (modulation coefficients were determined as the normalized difference between the maximal and minimal spike number in neuronal responses to all noises with notch exposed in the series). It was shown that the highest modulation coefficient values and accordingly the highest frequency-dependent sensitivity to spectral notches in the noise were peculiar to inhibition-dependent inferior colliculus neurons. Statistical analysis confirmed that distribution of modulation coefficients for the group of the inhibition-dependent neurons differed statistically significantly from the distribution for groups of primary-like and V-shaped inferior colliculus neurons as well as of cortical neurons (U-test, p < 0.0001). The lowest sensitivity to spectral notches was revealed in the V-shaped inferior colliculus neurons and cortical neurons; in these groups, distribution of modulation coefficients did not differed statistically significantly (p > 0.3). Thus, although a part of cortical neurons does have the frequency-dependent selectivity to spectral localizationally informative changes in sound signals, its formation needs participation of the inferior colliculus and its inhibition-dependent neurons. Selectivity to direction of the shift of spectral changes in noise signals in neurons of the inferior colliculus and auditory cortex was similar and was manifested mainly as shift along the frequency axis of dependences of the spike number in the neuronal responses and latent periods on central frequency of notch in noise (the noise band).     

GABA介导杏仁外侧核对皮层A Ⅰ区神经元声反应的抑制:在体微电泳研究

在SD大鼠上应用多顺利完成微电极方法,观察微电泳CABA及其受体的拮抗剂或激动剂对杏仁外侧核（LA）抑制皮层AⅠ神经元声反应效应的影响。结果显示,电泳GABA能抑制皮层AⅠ区神经元的电活动,电泳GABAA受体拮抗剂bicuculline（BIC）则能易化其反应;电刺激LA能抑制皮层AⅠ区听神经元声反应,电泳GABA产生类拟于刺激LA的抑制效应;LA对皮层AⅠ区神经的抑制效应能被BIC所翻转,而不能被什氨酸受体拮抗剂strychnine所翻转,电泳GABAB型受体例激动剂baclofen对神经元声反应无影响。上术结果表明,GABA可能是介民LA抑制皮层AⅠ区神经元声反应的最终递质,并且是通过GABAA受体作用的。     

Responses of electrosensory neurons in the torus semicircularis of Eigenmannia to complex beat stimuli: testing hypotheses of temporal filtering

The weakly electric fish, Eigenmannia, changes its frequency of electric organ discharges (EODs) to increase the frequency difference between its EODs and those of a jamming neighbor. This jamming avoidance response is greatest for frequency differences (i.e., beat rates) of approximately 4 Hz and barely detectable at beat rates of 20 Hz. A neural correlate of this behavior is found in the torus semicircularis, where most neurons act as low-pass or band-pass filters over this range of beat rates.This study examines two mechanisms that could possibly underlie low-pass temporal filtering: 1) Inhibition by a high-pass interneuron. 2) Voltage and time-dependent conductances associated with ligand-gated channels. These mechanisms were tested by recording intracellularly while employing stimuli consisting of simultaneous low and high beat rates. A neuron's response to the low beat rate was not diminished by the addition of the higher frequency jamming signal (thereby superimposing a high rate of amplitude and phase modulation onto the lower rate), and the inhibitory interneuron hypothesis is, therefore, not supported. Also, the responses to the high beat rate were not facilitated during maintained depolarization in response to the low beat rate.In some cases, particularly band-pass neurons, accommodation processes appeared to contribute to the decline in the amplitude of psps at high beat rates.