It has been empirically established that the cerebral cortical areas defined by Brodmann one hundred years ago solely on the basis of cellular organization are closely correlated to their function, such as sensation, association, and motion. Cytoarchitectonically distinct cortical areas have different densities and types of neurons. Thus, signaling patterns may also vary among cytoarchitectonically unique cortical areas. To examine how neuronal signaling patterns are related to innate cortical functions, we detected intrinsic features of cortical firing by devising a metric that efficiently isolates non-Poisson irregular characteristics, independent of spike rate fluctuations that are caused extrinsically by ever-changing behavioral conditions. Using the new metric, we analyzed spike trains from over 1,000 neurons in 15 cortical areas sampled by eight independent neurophysiological laboratories. Analysis of firing-pattern dissimilarities across cortical areas revealed a gradient of firing regularity that corresponded closely to the functional category of the cortical area; neuronal spiking patterns are regular in motor areas, random in the visual areas, and bursty in the prefrontal area. Thus, signaling patterns may play an important role in function-specific cerebral cortical computation.

Color has become a premier model system for understanding how information is processed by neural circuits, and for investigating the relationships among genes, neural circuits, and perception. Both the physical stimulus for color and the perceptual output experienced as color are quite well characterized, but the neural mechanisms that underlie the transformation from stimulus to perception are incompletely understood. The past several years have seen important scientific and technical advances that are changing our understanding of these mechanisms. Here, and in the accompanying minisymposium, we review the latest findings and hypotheses regarding color computations in the retina, primary visual cortex, and higher-order visual areas, focusing on non-human primates, a model of human color vision.In trichromatic primates, including humans and Old World monkeys, there are three types of cone photoreceptors that are responsible for color vision ( Fig. 1 A, B). The cone classes are called L, M, and S because of their spectral-sensitivity peaks, which lie in the long-, middle-, and short-wavelength regions of the visible spectrum. These labels replace the misleading terms "red," "green," and "blue." Two physically distinct stimuli appear as different colors only if they produce different relative activations in at least two cone types; conversely, any pair of physically distinct stimuli that activate the cone types in the same relative amount appear the same, like the two yellows shown in Figure 1C. While photoreceptor responses are easily computed from the spectral distribution of the stimulus, there is no straightforward relationship between photoreceptor response and color (Hofer et al., 2005a;Shevell and Kingdom, 2008). The multitude of color phenomena, including color afterimages, color assimilation, neon-color spreading, color constancy, and colored shadows, is compelling because in many cases two physically identical stimuli are made to appear different colors, or two physically different stimuli are made to appear the same simply by changing the spatial or temporal context (Fig. 2). A full description of the neural machinery for color should account for these observations, as well as more cognitive phenomena involving the relationship between experience, language, memory, emotion and color. The neural basis of color has been reviewed previously from a range of perspectives (Gegenfurtner, 2003;Gegenfurtner and Kiper, 2003;Lennie and Movshon, 2005;Sincich and Horton, 2005;Solomon and Lennie, 2007;Conway, 2009;Dobkins, 2009;Jacobs and Nathans, 2009;Stockman and Brainard, 2010). Here we focus on advances and pressing questions regarding the mechanisms of color in retina, striate cortex, and extrastriate cortex of non-human primates, although we note that other species are emerging as excellent model systems of color processing (Lotto and Chittka, 2005;Van Hooser and Nelson, 2006;Osorio and Vorobyev, 2008;Borst, 2009;Johnson et al., 2010;Srinivasan, 2010). Retinal mechanismsA single cone by itself is color blind b...

An ultrastretchable film device is developed that can follow the shape of spherical and large deformable biological samples such as heart and brain tissues. Although the film is composed of biocompatible parylene for the device substrate and metal layers of platinum (Pt)/titanium (Ti), which are unstretchable materials, the film shows a high stretchability by patterning slits as a "Kirigami" design. A Pt/Ti-microelectrode array embedded in 11 µm thick parylene film with 5 × 91 slits exhibits a film strain of ≈250% at 9 mN strain-force (0.08 MPa in stress) with a Young's modulus of 23 kPa, while the 3 × 91-slit film shows a Young's modulus of 3.6 kPa. The maximum strains of these devices are ≈470% and ≈840%, respectively. It is demonstrated that the Kirigami-based microelectrode device can simultaneously record in vivo electrocorticogram signals from the visual and barrel cortices of a mouse by stretching the film and tuning the electrode gap. Moreover, wrapping the Kirigami device around a beating mouse's heart, which shows large and rapid changes in the volume and the surface area, can record the in vivo epicardial electrocardiogram signals. Such a small Young's modulus for a stretchable device reduces the device's strain-force, minimizing the device-induced stress to soft biological tissues.

Categorization and fine discrimination are two different functions in visual perception, and we can switch between these two functions depending on the situation or task demands. To explore how visual cortical neurons behave in such situations, we recorded the activities of color-selective neurons in the inferior temporal (IT) cortex of two monkeys trained to perform a color categorization task, a color discrimination task and a simple fixation task. Many IT neurons changed their activity depending upon the task, although color selectivity was well conserved. A majority of neurons showed stronger responses during the categorization task. Moreover, for the population of IT neurons as a whole, signals contributing to performing the categorization task were enhanced. These results imply that judgment of color category by color-selective IT neurons is facilitated during the categorization task and suppressed during the discrimination task as a consequence of task-dependent modulation of their activities.

The architectonic subdivisions of the brain are believed to be functional modules, each processing parts of global functions. Previously, we showed that neurons in different regions operate in different firing regimes in monkeys. It is possible that firing regimes reflect differences in underlying information processing, and consequently the firing regimes in homologous regions across animal species might be similar. We analyzed neuronal spike trains recorded from behaving mice, rats, cats, and monkeys. The firing regularity differed systematically, with differences across regions in one species being greater than the differences in similar areas across species. Neuronal firing was consistently most regular in motor areas, nearly random in visual and prefrontal/medial prefrontal cortical areas, and bursting in the hippocampus in all animals examined. This suggests that firing regularity (or irregularity) plays a key role in neural computation in each functional subdivision, depending on the types of information being carried.Key words: firing irregularity/regularity; interspecies similarity; neuronal firing pattern; neuronal firing regime Significance StatementBy analyzing neuronal spike trains recorded from mice, rats, cats, and monkeys, we found that different brain regions have intrinsically different firing regimes that are more similar in homologous areas across species than across areas in one species. Because different regions in the brain are specialized for different functions, the present finding suggests that the different activity regimes of neurons are important for supporting different functions, so that appropriate neuronal codes can be used for different modalities.

The spatial luminance relationship between shading patterns and specular highlight is suggested to be a cue for perceptual translucency (Motoyoshi, 2010). Although local image features are also important for translucency perception (Fleming & Bulthoff, 2005), they have rarely been investigated. Here, we aimed to extract spatial regions related to translucency perception from computer graphics (CG) images of objects using a psychophysical reverse-correlation method. From many trials in which the observer compared the perceptual translucency of two CG images, we obtained translucency-related patterns showing which image regions were related to perceptual translucency judgments. An analysis of the luminance statistics calculated within these image regions showed that (1) the global rms contrast within an entire CG image was not related to perceptual translucency and (2) the local mean luminance of specific image regions within the CG images correlated well with perceptual translucency. However, the image regions contributing to perceptual translucency differed greatly between observers. These results suggest that perceptual translucency does not rely on global luminance statistics such as global rms contrast, but rather depends on local image features within specific image regions. There may be some “hot spots” effective for perceptual translucency, although which of many hot spots are used in judging translucency may be observer dependent.

Categorical perception is a ubiquitous function in sensory information processing, and is reported to have important influences on the recognition of presented and/or memorized stimuli. However, such complex interactions among categorical perception and other aspects of sensory processing have not been explained well in a unified manner. Here, we propose a recurrent neural network model to process categorical information of stimuli, which approximately realizes a hierarchical Bayesian estimation on stimuli. The model accounts for a wide variety of neurophysiological and cognitive phenomena in a consistent framework. In particular, the reported complexity of categorical effects, including (i) task-dependent modulation of neural response, (ii) clustering of neural population representation, (iii) temporal evolution of perceptual color memory, and (iv) a non-uniform discrimination threshold, are explained as different aspects of a single model. Moreover, we directly examine key model behaviors in the monkey visual cortex by analyzing neural population dynamics during categorization and discrimination of color stimuli. We find that the categorical task causes temporally-evolving biases in the neuronal population representations toward the focal colors, which supports the proposed model. These results suggest that categorical perception can be achieved by recurrent neural dynamics that approximates optimal probabilistic inference in the changing environment.

. Earlier studies suggest that the inferior temporal (IT) cortex of the monkey plays a key role in color discrimination. Here, we examined the quantitative relationship between color judgment in monkeys and the responses of colorselective neurons in the anterior part of the IT cortex (area TE) by comparing neuronal activity and behavior recorded simultaneously while the monkeys performed a color-judgment task. We first compared the abilities of single neurons and monkeys to discriminate color. To calculate a neuron's ability to discriminate color, we computed a neurometric function using receiver-operating-characteristics analysis. We then compared the neural and behavioral thresholds for color discrimination and found that, in general, the neural threshold was higher than the behavioral threshold, although occasionally the reverse was true. Variation in the neural threshold across the color space corresponded well with that of the behavioral threshold. We then calculated the choice probability (CP), which is a measure of the correlation between the trial-to-trial fluctuations in neuronal responses and the monkeys' color judgment. On average, CPs were slightly but significantly greater than 0.5, indicating the activities of these TE neurons correlate positively with the monkeys' color judgment. This suggests that individual color-selective TE neurons only weakly contribute to color discrimination and that a large population of color-selective TE neurons contribute to the performance of color discrimination. I N T R O D U C T I O NIn the cerebral cortex of the monkey, color information is transmitted along the ventral visual stream, which includes areas V1, V2, and V4, until it ultimately reaches the inferior temporal (IT) cortex (Conway and Tsao 2006; Desimone et al. 1984; Fujita et al. 1992;Komatsu 1998;Komatsu et al. 1992;Maunsell and Newsome 1987;Tootell et al. 2004;Zeki 2005;). Several studies have shown that lesioning or cooling the IT cortex seriously impairs color discrimination (Buckley et al. 1997; Dean 1979; Heywood et al. 1995; Horel 1994; Huxlin et al. 2000); moreover, neural recording studies have shown that many neurons in the IT cortex selectively respond to specific colors (Desimone et al. 1984;Kobatake and Tanaka 1994;Koida and Komatsu 2007;Komatsu and Ideura 1993;Komatsu et al. 1992;Zeki 1996). These neurons are narrowly tuned to various hues and saturation of color and appear to be concentrated in several subregions of the IT cortex, including areas TE and TEO (Conway et al. 2007;Yasuda and Komatsu 2005;Yasuda et al. 2004). Although it is natural to assume that these color-selective neurons play important roles in color discrimination, there has been no study in which this issue was systematically examined.Our aim in the present study was to quantitatively examine the relationship between the activity of color-selective TE neurons and color-discrimination behavior in the monkey. We have concentrated on TE, where neurons have large receptive fields including the fovea, and the recorded area ...