Neurophysiological mechanisms underlying face processing within and beyond the temporal cortical visual areas.

The ways in which information about faces is represented and stored in the temporal lobe visual areas of primates, as shown by recordings from single neurons in macaques, are considered. Some neurons that respond primarily to faces are found in the cortex in the anterior part of the superior temporal sulcus (in which neurons are especially likely to be tuned to facial expression and to face movement involved in gesture), and in the TE areas more ventrally forming the inferior temporal gyrus (in which neurons are more likely to have responses related to the identity of faces). Quantitative studies of the responses of the neurons that respond differently to the faces of different individuals show that information about the identity of the individual is represented by the responses of a population of neurons, that is, ensemble encoding rather than 'grandmother cell' encoding is used. It is argued that this type of tuning is a delicate compromise between very fine tuning, which has the advantage of low interference in neuronal network operations but the disadvantage of losing the useful properties (such as generalization, completion and graceful degradation) of storage in neuronal networks, and broad tuning, which has the advantage of allowing these properties of neuronal networks to be realized but the disadvantage of leading to interference between the different memories stored in an associative network. There is evidence that the responses of some of these neurons are altered by experience so that new stimuli become incorporated in the network. It is shown that the representation that is built in temporal cortical areas shows considerable invariance for size, contrast, spatial frequency and translation. Thus the representation is in a form which is particularly useful for storage and as an output from the visual system. It is also shown that one of the representations that is built is object based, which is suitable for recognition and as an input to associative memory, and that another is viewer centred, which is appropriate for conveying information about gesture. Ways are considered in which such cortical representations might be built by competitive self-organization aided by back projections in the multi-stage cortical processing hierarchy which has convergence from stage to stage.     

A model cortical circuit for the storage of temporal sequences

Despite the fact that temporal information processing is of particular significance in biological memory systems, not much has yet been explored about how these systems manage to store temporal information involved in sequences of stimuli. A neural network model capable of learning and recalling temporal sequences is proposed, based on a neural mechanism in which the sequences are expanded into a series of periodic rectangular oscillations. Thus, the mathematical framework underlying the model, to some extent, is concerned with the Walsh function series. The oscillatory activities generated by the interplay between excitatory and inhibitory neuron pools are transmitted to another neuron pool whose role in learning and retrieval is to modify the rhythms and phases of the rectangular oscillations. Thus, a basic functional neural circuit involves three different neuron pools. The modifiability of rhythms and phases is incorporated into the model with the aim of improving the quality of the retrieval. Numerical simulations were conducted to show the characteristic features of the learning as well as the performance of the model in memory recall.     

Large-scale modeling of the primary visual cortex: influence of cortical architecture upon neuronal response.

A large-scale computational model of a local patch of input layer 4 [Formula: see text] of the primary visual cortex (V1) of the macaque monkey, together with a coarse-grained reduction of the model, are used to understand potential effects of cortical architecture upon neuronal performance. Both the large-scale point neuron model and its asymptotic reduction are described. The work focuses upon orientation preference and selectivity, and upon the spatial distribution of neuronal responses across the cortical layer. Emphasis is given to the role of cortical architecture (the geometry of synaptic connectivity, of the ordered and disordered structure of input feature maps, and of their interplay) as mechanisms underlying cortical responses within the model. Specifically: (i) Distinct characteristics of model neuronal responses (firing rates and orientation selectivity) as they depend upon the neuron's location within the cortical layer relative to the pinwheel centers of the map of orientation preference; (ii) A time independent (DC) elevation in cortico-cortical conductances within the model, in contrast to a "push-pull" antagonism between excitation and inhibition; (iii) The use of asymptotic analysis to unveil mechanisms which underly these performances of the model; (iv) A discussion of emerging experimental data. The work illustrates that large-scale scientific computation--coupled together with analytical reduction, mathematical analysis, and experimental data, can provide significant understanding and intuition about the possible mechanisms of cortical response. It also illustrates that the idealization which is a necessary part of theoretical modeling can outline in sharp relief the consequences of differing alternative interpretations and mechanisms--with final arbiter being a body of experimental evidence whose measurements address the consequences of these analyses.     

A quantitative morphometric comparative analysis of the primate temporal lobe

Given their importance in language comprehension, the human temporal lobes and/or some of their component structures might be expected to be larger than allometric predictions for a nonhuman anthropoid brain of human size. Whole brain, T1-weighted MRI scans were collected from 44 living anthropoid primates spanning 11 species. Easyvision software (Philips Medical Systems, The Netherlands) was used to measure the volume of the entire brain, the temporal lobes, the superior temporal gyri, and the temporal lobe white matter. The surface areas of both the entire temporal lobe and the superior temporal gyrus were also measured, as was temporal cortical gyrification.Allometric regressions of temporal lobe structures on brain volume consistently showed apes and monkeys to scale along different trajectories, with the monkeys typically lying at a higher elevation than the apes. Within the temporal lobe, overall volume, surface area, and white matter volume were significantly larger in humans than predicted by the ape regression lines. The largest departure from allometry in humans was for the temporal lobe white matter volume which, in addition to being significantly larger than predicted for brain size, was also significantly larger than predicted for temporal lobe volume. Among the nonhuman primate sample, Cebus have small temporal lobes for their brain size, and Macaca and Papio have large superior temporal gyri for their brain size. The observed departures from allometry might reflect neurobiological adaptations supporting species-specific communication in both humans and old world monkeys.     

Tetrahymena cells and the quantitative two-phase assay: visual assessment of chemokinesis and gravikinesis

Ginkgo biloba extract (GBE), which is one of the most sold herbal extracts in the world, is considered as a multifunctional material, which can promote radical scavenging activity and improve brain functioning. Although much research has carried out on its mechanisms against diseases, there is a need for further investigation for understanding molecular mechanisms, potential health benefits, and possible health risks. Recently, we have been developing an alternative screening method for studying phytochemical materials bioactivities with Tetrahymena thermophila as experimental organism. In this paper, the effects of GBE and its constituents were systematically investigated on chemoattraction and cGMP-dependent protein kinase (PKG) in T. thermophila . GBE and its constituents exerted significant inhibitions of chemoattraction and PKG. The minimal concentrations to completely inhibit chemotaxis of T. thermophila were 2 mg/ml, 50, 25, 12, 100, 100, 400, 500, 300 and 400 μM for GBE, quercetin, kaempferol, isorhamnetin, myricetin, genistein, rutin, quercitrin, isoquercitrin and quercetin-3- d -galactoside, respectively. The IC₅₀ values for PKG were 0.15 mg/ml, 26, 22, 19, 160, 132, 81 and 186 μM for GBE, myricetin, kaempferol, quercetin, isorhamnetin, genistein, rutin and isoquercitrin, respectively. The results indicate that the inhibitions of GBE and its constituents of chemotaxis of T. thermophila and their effects on PKG are rather similar. This suggests that the ciliate of T. thermophila may be a potential experimental organism in screening such bioactive phytochemicals.     

Projections from cortical visual areas of the superior temporal sulcus to the superior colliculus, in macaque monkeys.

1. The distribution of tectal projections of two visual areas of the superior temporal sulcus (MT and MST areas) has been studied, in five Macaca fascicularis, by means of the autoradiographic method tracing the anterograde transport of tritiated aminoacids intracortically injected. 2. In all cases the ipsilateral superior colliculi (SC) were found labelled, whereas the contralateral ones were devoid of label. 3. The three brains injected in the MT area resulted in SC labels that involved the superficial gray layer (SGS), the stratum opticum (SO) and the intermediate gray layer (SGI), sparing the layers below SGI. 4. The collicular labels found after injections within the MST area exhibited their distribution over the deep SC subdivision, whereas they spared all the superficial layers but the deep part of the SO. 5. In two animals with large uptake zones, one in MT and the other in MST, the labelling within the SGI showed a cluster-like pattern. 6. The distinct found bulk of projections of MT and MST respectively to the superficial and deep subdivisions of the SC, along with a number of peculiar connections of the MST area as mentioned in the text, contribute to depict an overall neural network in which MST appears to be more strongly involved than MT in linking sensory visual with oculomotor attentive functions.     

Nanoindentation response of cortical bone: dependency of subsurface voids

Nanoindentation test results in the axial direction of mouse femurs were the basis for the current study. Although the majority of the nanoindentation curves showed a reasonable consistency, some curves showed a significantly softer response. Detailed investigation, using focused ion beam-scanning electron microscopy, provided that the softer response is due to subsurface cavities such as lacunae. Finite element models were developed to simulate the nanoindentation of mice femur cortical bone samples with and without the incorporation of a single lacuna underneath the bone surface. Based on the material parameters determined for the cavity-free tissue, numerical simulations were run for different cases of cavity size, shape, and location. Spherical cavities with different size were considered at different distances from the surface. The results showed that subsurface cavities can lead to 50% higher indentation compared to an indentation in cavity-free material. Continuing with ellipsoidal cavities with the center located on the load axis, the results showed a nonlinear dependency of ellipsoid shape. Hence, the shape of the cavity is important for the nanoindentation response. The influence of horizontal and vertical offsets of spherical cavities was studied, thereby the results showed that an increasing horizontal offset caused a decreasing influence of the vertical distance from the surface. In perspective, the present study provides information that may help to get deeper knowledge of nanoindentation load–displacement mechanism taking place in samples with subsurface cavities.     

Laminar processing in the visual cortical column

Sensory regions of neocortex are organized as arrays of vertical columns composed of cells that share similar response properties, with the orientation columns of the cat's visual cortex being the best known example. Interest in how sensitivity to different stimulus features first emerges in the columns and how this selectivity is refined by subsequent processing has fueled decades of research. A natural starting point in approaching these issues is anatomy. Each column traverses the six cortical layers and each layer has a unique pattern of inputs, intrinsic connections and outputs. Thus, it makes sense to explore the possibility of corresponding laminar differences in sensory function, that is, to examine relationships between morphology and physiology. In addition, to help identify general patterns of cortical organization, it is useful to compare results obtained from different sensory systems and diverse species. The picture that emerges from such comparisons is that each cortical layer serves a distinct role in sensory function. Furthermore, different cortices appear to share some common strategies for processing information but also have specialized mechanisms adapted for the demands of specific sensory tasks.     

A quantitative method for the evaluation of three-dimensional structure of temporal bone pneumatization

Temporal bone pneumatization has been included in lists of characters used in phylogenetic analyses of human evolution. While studies suggest that the extent of pneumatization has decreased over the course of human evolution, little is known about the processes underlying these changes or their significance. In short, reasons for the observed reduction and the potential reorganization within pneumatized spaces are unknown. Technological limitations have limited previous analyses of pneumatization in extant and fossil species to qualitative observations of the extent of temporal bone pneumatization. In this paper, we introduce a novel application of quantitative methods developed for the study of trabecular bone to the analysis of pneumatized spaces of the temporal bone. This method utilizes high-resolution X-ray computed tomography (HRXCT) images and quantitative software to estimate three-dimensional parameters (bone volume fractions, anisotropy, and trabecular thickness) of bone structure within defined units of pneumatized spaces. We apply this approach in an analysis of temporal bones of diverse but related primate species, Gorilla gorilla, Pan troglodytes, Homo sapiens, and Papio hamadryas anubis, to illustrate the potential of these methods. In demonstrating the utility of these methods, we show that there are interspecific differences in the bone structure of pneumatized spaces, perhaps reflecting changes in the localized growth dynamics, location of muscle attachments, encephalization, or basicranial flexion.     

Transmission of electric fields in cortical tissue: A model for the origin of the alpha rhythm

A mathematical model of the cortex is developed, in which a great many independently-firing sources of voltage pulses are assumed to be imbedded in a diffusive medium of indefinite extent. In such a medium, characterized by a conductivity and a capacitivity (capacitance per unit volume), electrical disturbances diffuse in a manner analogous to the conduction of heat in solids. Assuming random firing of the individual pulse sources (which simulate neurons) and invoking Campbell's Theorem, the power spectrum of the voltage appearing at any point within the medium can be calculated. As a consequence of the positive after-potential in the neural discharge (which is shown to be a physical necessity), the power spectrum is found to contain a single low-frequency peak. For reasonable parameter values, this peak appears at very near the classical alpha frequency of ten cycles per second. The related phenomena of evoked potentials, alpha blocking, and photic driving are also discussed in terms of the model.