Formation of a mosaic of neuronal activity from microfoci of excitation in rat cerebral cortex

Responses of several neurons from area 17 in the rat visual cortex to illumination with round spots of growing size were recorded. The size and shape of receptive fields of the neurons were determined. When the spot was placed into the central part of the receptive fields of neurons situated along one vertical run, distribution analysis of excited, inhibited, and non-responding neurons here showed that microlocus of excitation was being formed in the middle layers of the visual cortex. As the spot became larger, the neuronal ensemble "grew" up to a certain critical size, beyond which the microlocus of excitation divided, and the mosaic of neuronal ensembles began to form reaching maximal clear-cutness of diffuse illumination of the eye.     

Chromatic induction: border contrast or adaptation to surrounding light?

Chromatic induction from a surrounding light is measured with an additional remote field outside the surround. Chromatic induction from the surround into a central test field is found to be attenuated by a remote inhomogeneous 'checkerboard', composed of squares at two different chromaticities. A uniform remote field, on the other hand, either at the average or at the most extreme chromaticity of the 'checkerboard', has a weaker effect on chromatic induction than the inhomogeneous field, implying that chromatic contrast within the remote region is a critical factor. The complete set of experiments is accounted for by chromatic contrast gain control: chromatic induction, mediated by a neural signal for contrast at the edge of the test, is attenuated by contrast within the remote region. A contrast gain control set by variation in chromaticity over a broad area can contribute to the stable color appearance of surfaces embedded within complex scenes by minimizing chromatic induction from locally adjacent regions.     

Visuospatial properties of ventral premotor cortex

In macaque ventral premotor cortex, we recorded the activity of neurons that responded to both visual and tactile stimuli. For these bimodal cells, the visual receptive field extended from the tactile receptive field into the adjacent space. Their tactile receptive fields were organized topographically, with the arms represented medially, the face represented in the middle, and the inside of the mouth represented laterally. For many neurons, both the visual and tactile responses were directionally selective, although many neurons also responded to stationary stimuli. In the awake monkeys, for 70% of bimodal neurons with a tactile response on the arm, the visual receptive field moved when the arm was moved. In contrast, for 0% the visual receptive field moved when the eye or head moved. Thus the visual receptive fields of most "arm + visual" cells were anchored to the arm, not to the eye or head. In the anesthetized monkey, the effect of arm position was similar. For 95% of bimodal neurons with a tactile response on the face, the visual receptive field moved as the head was rotated. In contrast, for 15% the visual receptive field moved with the eye and for 0% it moved with the arm. Thus the visual receptive fields of most "face + visual" cells were anchored to the head, not to the eye or arm. To construct a visual receptive field anchored to the arm, it is necessary to integrate the position of the arm, head, and eye. For arm + visual cells, the spontaneous activity, the magnitude of the visual response, and sometimes both were modulated by the position of the arm (37%), the head (75%), and the eye (58%). In contrast, to construct a visual receptive field that is anchored to the head, it is necessary to use the position of the eye, but not of the head or the arm. For face + visual cells, the spontaneous activity and/or response magnitude was modulated by the position of the eyes (88%), but not of the head or the arm (0%). Visual receptive fields anchored to the arm can encode stimulus location in "arm-centered" coordinates, and would be useful for guiding arm movements. Visual receptive fields anchored to the head can likewise encode stimuli in "head-centered" coordinates, useful for guiding head movements. Sixty-three percent of face + visual neurons responded during voluntary movements of the head. We suggest that "body-part-centered" coordinates provide a general solution to a problem of sensory-motor integration: sensory stimuli are located in a coordinate system anchored to a particular body part.     

Overjet reduction and molar correction in fixed appliance treatment of class II, division 1, malocclusions: sagittal and vertical components

A magnetic field exposure laboratory has been constructed to support National Toxicology Program studies for the evaluation of the toxicity and carcinogenicity of pure, linearly polarized, 60 Hz magnetic fields in rodents. This dual corridor, controlled access facility can support the simultaneous exposure of 1200 rats and 1200 mice. The facility contains fully redundant electrical and environmental control systems and was constructed using non-metallic materials to maintain low levels of background (ambient), stray, and cross-talk magnetic fields. The exposure module design provides for large uniform exposure volumes with good control of stray and cross-talk fields, while allowing the use of roll-around cage racks for simplified animal husbandry. Stray fields and cross-talk have been further reduced by the inclusion of "steering coils" in each exposure module. Ambient 60 Hz fields (less cross-talk) in all exposure rooms are <0.1 microT (1 mG), and static magnetic fields have been mapped extensively. Magnetic field strength, waveform, temperature, relative humidity, light intensity, noise level, vibration, and air flow in all animal holding areas are tightly regulated, and are monitored continuously during all studies. Field uniformity in the animal exposure volumes is better than -/+l0%; a systematic program of cage, rack, and room rotation controls for possible positional effects within the exposure system. Magnetic fields are turned on and off over multiple cycles to prevent the induction of transients associated with abrupt field level changes. Total harmonic distortion is <3% at all field strengths. The facility has been used to study magnetic field bioeffects in rodent model systems in experiments ranging in duration from 8 weeks to 2 years.     

Functional organization of owl monkey lateral geniculate nucleus and visual cortex

The nocturnal, New World owl monkey (Aotus trivirgatus) has a rod-dominated retina containing only a single cone type, supporting only the most rudimentary color vision. However, it does have well-developed magnocellular (M) and parvocellular (P) retinostriate pathways and striate cortical architecture [as defined by the pattern of staining for the activity-dependent marker cytochrome oxidase (CO)] similar to that seen in diurnal primates. We recorded from single neurons in anesthetized, paralyzed owl monkeys using drifting, luminance-modulated sinusoidal gratings, comparing receptive field properties of M and P neurons in the lateral geniculate nucleus and in V1 neurons assigned to CO "blob," "edge," and "interblob" regions and across layers. Tested with achromatic stimuli, the receptive field properties of M and P neurons resembled those reported for other primates. The contrast sensitivity of P cells in the owl monkey was similar to that of P cells in the macaque, but the contrast sensitivities of M cells in the owl monkey were markedly lower than those in the macaque. We found no differences in eye dominance, orientation, or spatial frequency tuning, temporal frequency tuning, or contrast response for V1 neurons assigned to different CO compartments; we did find fewer direction-selective cells in blobs than in other compartments. We noticed laminar differences in some receptive field properties. Cells in the supragranular layers preferred higher spatial and lower temporal frequencies and had lower contrast sensitivity than did cells in the granular and infragranular layers. Our data suggest that the receptive field properties across functional compartments in V1 are quite homogeneous, inconsistent with the notion that CO blobs anatomically segregate signals from different functional "streams."     

A model for the neuronal implementation of selective visual attention based on temporal correlation among neurons

We propose a model for the neuronal implementation of selective visual attention based on temporal correlation among groups of neurons. Neurons in primary visual cortex respond to visual stimuli with a Poisson distributed spike train with an appropriate, stimulus-dependent mean firing rate. The spike trains of neurons whose receptive fields do not overlap with the "focus of attention" are distributed according to homogeneous (time-independent) Poisson process with no correlation between action potentials of different neurons. In contrast, spike trains of neurons with receptive fields within the focus of attention are distributed according to non-homogeneous (time-dependent) Poisson processes. Since the short-term average spike rates of all neurons with receptive fields in the focus of attention covary, correlations between these spike trains are introduced which are detected by inhibitory interneurons in V4. These cells, modeled as modified integrate-and-fire neurons, function as coincidence detectors and suppress the response of V4 cells associated with non-attended visual stimuli. The model reproduces quantitatively experimental data obtained in cortical area V4 of monkey by Moran and Desimone (1985).     

Dynamic properties of Lednev's parametric resonance mechanism

This paper presents a further development of the mechanism for the detection of weak magnetic fields proposed by [Lednev (1991): Bioelectromagnetics 12:71-75]. The fraction of excited oscillator states of an unhydrated ion is studied in a dynamic model driven by the predicted (time-varying) transition probability in the presence of thermal noise and an unspecified excitation mechanism. The main results of Lednev are confirmed. In addition, I conclude that ultraharmonic and ultrasubharmonic resonances may also be observed, provided that the response time of the dynamic system is similar to the period of the oscillating magnetic field. I discuss the time scales involved in the mechanism and present theoretical constraints on these parameters. The crucial requirement for the theory's applicability is that the lifetime of the excited states of the affected ion oscillator exceeds the period of the applied magnetic field. Numerical solutions of the dynamic system are given and are shown to correspond well to theoretical expectations. The main discrepancy between the theories of Lednev and of Blanchard and Blackman [Blanchard and Blackman (1994): Bioelectromagnetics 15:217-238] appears to be due to an inconsistency in the latter paper. The general problem of robust analysis of experimental data is discussed, and I suggest a test of compliance with the Lednev model that is independent of all parameters except for the ratio of oscillating and static field strength (B1/B0) for many resonance conditions and experimental models.     

The cone/horizontal cell network: a possible site for color constancy

Color vision is spectrally opponent, suggesting that spectrally opponent neurons, such as the horizontal cells in fish and turtle retinae, play a prominent role in color discrimination. In the accompanying paper (Kraaij et al., 1998), it was shown that the output signal of the horizontal cell system to the cones is not at all spectrally opponent. Therefore, a role for the spectrally opponent horizontal cells in color discrimination seems unlikely. In this paper, we propose that the horizontal cells play a prominent role in color constancy and simultaneous color contrast instead of in color discrimination. We have formulated a model of the cone/horizontal cell network based on measurements of the action spectra of the cones and of the feedback signal of the horizontal cell system to the various cone types. The key feature of the model is (1) that feedback is spectrally and spatially very broad and (2) that the gain of the cone synapse strongly depends on the feedback strength. This makes the synaptic gain of the cones strongly dependent on the spectral composition of the surround. Our model, which incorporates many physiological details of the outer retina, displays a behavior that can be interpreted as color constancy and simultaneous color contrast. We propose that the horizontal cell network modulates the cone synaptic gains such that the ratios of the cone outputs become almost invariant with the spectral composition of the global illumination. Therefore, color constancy appears to be coded in the retina.     

Transient and long-lasting effects of iontophoretically administered norepinephrine on somatosensory cortical neurons in halothane-anesthetized cats

We examined the modulatory effects of iontophoretically administered norepinephrine (NE) on the excitability of 117 neurons in cat somatosensory cortex. NE was released in the vicinity of neurons with receptive fields (31/117) while they were excited by somatic stimuli and near neurons without receptive fields (86/117) while they were excited by glutamate. In 54% of the neurons (n = 63) the effects were inhibitory, decreasing both the spontaneous and the driven activity. Most of these cells were found in the middle layers of cortex. In 36% of the neurons (n = 42), mostly located in either the upper or lower layers, the effects were excitatory, enhancing either or both driven and spontaneous activity, but 52% (n = 22) of this group displayed a transient phase of inhibition. NE usually had a proportionately greater effect on the spontaneous activity than on the evoked activity. Effects of specific NE agonists and antagonists indicated that alpha 2- and beta-receptors mediated the inhibition, but that alpha 1-receptors mediated the excitation. We hypothesize that when NE is released in cat somatosensory cortex, it modulates neuronal responses to afferent activity by generally reducing the excitability of cells in the middle layers and by increasing their signal-to-noise ratios. However, in the upper and lower layers NE will enhance neuronal activity, encouraging exchanges with other cortical areas. In addition, we tested and confirmed the hypothesis that short treatments with NE can modify the excitability of neurons in adult cat somatosensory cortex for long periods of time. Of 69 cells, 59% showed effects of NE lasting for more than 5 min. Response enhancement lasting for the duration of the recording session (5 to 36 min) occurred in 82% (18/22) of silent cells without a receptive field and in 63% (17/27) of spontaneously active cells without a receptive field, but only in 14% (2/14) of cells with a receptive field, suggesting an inverse relationship between cell excitability and this effect of NE. The magnitude of the enhancement followed the same relationship, being greatest for silent cells and least for cells with receptive fields (125, 58, and 49%, respectively). The long-lasting enhancement was blocked by an alpha 1-receptor antagonist in 6 of 9 neurons tested, while the administration of alpha 2- and beta-receptor agonists never produced a long-lasting effect, suggesting that the effect is mediated by alpha 1-adrenoceptors.     

An empirical explanation of brightness

The striking illusions produced by simultaneous brightness contrast generally are attributed to the center-surround receptive field organization of lower order neurons in the primary visual pathway. Here we show that the apparent brightness of test objects can be either increased or decreased in a predictable manner depending on how light and shadow are portrayed in the scene. This evidence suggests that perceptions of brightness are generated empirically by experience with luminance relationships, an idea whose implications we pursue in the accompanying paper.     

Influence of centrifugal pathways on forward masking of ventral cochlear nucleus neurons

When responses to one part of a sequence of auditory signals reduce the responses to a subsequent portion of the signal, "forward masking" results. Although forward masking occurs in the auditory nerve, that observed in the ventral cochlear nucleus (VCN) more closely resembles psychophysical forward masking. In contrast to the auditory nerve in which the amount of forward masking is proportional to the amount of excitation produced by the masker, most VCN neurons show a poor correlation between forward masking and excitation produced by the masker, indicating a more complex interaction between responses to adjacent signals. This study tested the hypothesis that one component of forward masking is produced by inputs from centrifugal neural connections to the VCN. The centrifugal pathways were interrupted with knife-cut lesions medial to the CN. Responses of single units obtained 60 minutes after the lesions were compared to those obtained before the lesions. In primarylike, sustained chopper and on units the lesions resulted in a reduction in forward masking and enhanced recovery. In contrast, lesions resulted in increased masking in primarylike-notch and low-intensity chopper units. The relationship between masker-elicited excitation and forward masking became more monotonic for transient choppers and on units, approaching that observed for auditory nerve fibers. These effects are probably the result of removal of both inhibitory and excitatory inputs, ultimately reflecting a balance of excitation and inhibition to each neural population in the VCN.     

Hippocampal place fields: relationship between degree of field overlap and cross-correlations within ensembles of hippocampal neurons

The capacity to record from multiple neurons in awake freely moving animals provides a means for characterizing organizational principles of place field encoding within ensembles of hippocampal neurons. In this study, cross-correlations between pairs of hippocampal place cells and degree of overlap between their respective place fields were analyzed during behavioral performance of delayed matching (DMS) or non-matching sample (DNMS) tasks, or while the same rats chased pellets in a different environment. The relationship between field overlap and cross-correlations of neural spike activity within ensembles was shown to be a positive, exponentially increasing, function. Place fields from the same neurons were markedly "remapped" between the Delay and Pellet-chasing tasks, with respect to physical location and size of fields. However individual pairs of place cells within each ensemble retained nearly the same degree of overlap and cross-correlation even though the spatial environment and the tasks differed markedly. This suggested that place cells were organized in functional "clusters" which exhibited the same inter-relations with respect to place field overlap and cross-correlations, irrespective of actual field of location. When cross-correlations between place cells were compared to placement of the array recording electrodes within the hippocampus, the strongest correlations were found along previously defined posterior-projecting fiber gradients between CA3 and CA1 subfields (Ishizuka et al. [1990], J Comp Neurol 295:580-623; Li et al. [1994] (J Comp Neurol 339:181-208). These findings suggest that the functional organization of place fields conforms to anatomical principles suspected to operate within hippocampal ensembles.     

Differential roles of p300 and PCAF acetyltransferases in muscle differentiation

To determine the possibility of discriminating multi-sources in the brain by 3D vector magnetic field measurement of a magnetoencephalogram (MEG), measurements were made of magnetic fields produced by two current dipoles implanted in a spherical head model. The 3D vector magnetic field measurements were made by using a 3D second-order gradiometer connected to three rf-SQUIDs, which can detect magnetic field components perpendicular to and tangential to the scalp. The MEG distribution measuring the magnetic field perpendicular to the scalp was not helpful in estimating the location and number of sources because of the lack of a dipole pattern. By referring to the MEG distribution measuring the magnetic field distribution tangential to the scalp, however, two current sources could be clearly discriminated in a spherical head model. It was found that this MEG distribution measuring tangential to the scalp could provide information on new constraint conditions for the calculation of inverse problems with multi-sources. These results were also confirmed by measurement of the mixed somatosensory evoked fields elicited by simultaneous electric stimulation to the median nerve and the thumb.     

Brightness induction from uniform and complex surrounds: a general model

We studied the brightness induced from complex non-figural achromatic surrounds. A spatially uniform test field was surrounded by a random texture composed of two sets of dots. The luminance of each set of dots was modulated sinusoidally at 0.5 Hz. The mean luminance, phase and amplitude of modulation of each set were controlled independently so as to modulate the luminance and/or the contrast of the surround. Brightness induction was measured by a modulation nulling technique. The results were fit by a model in which the total brightness induced by a surround is equal to a weighted spatial summation of the induced effects from each point in the surround. The model incorporates local luminance gain controls in the test and surround fields and assumes that the magnitude of induction from each surround element is gain controlled by the difference between the mean luminance of the test and the individual surround elements.     

Contrast-invariant orientation tuning in cat visual cortex: thalamocortical input tuning and correlation-based intracortical connectivity

The origin of orientation selectivity in visual cortical responses is a central problem for understanding cerebral cortical circuitry. In cats, many experiments suggest that orientation selectivity arises from the arrangement of lateral geniculate nucleus (LGN) afferents to layer 4 simple cells. However, this explanation is not sufficient to account for the contrast invariance of orientation tuning. To understand contrast invariance, we first characterize the input to cat simple cells generated by the oriented arrangement of LGN afferents. We demonstrate that it has two components: a spatial-phase-specific component (i.e., one that depends on receptive field spatial phase), which is tuned for orientation, and a phase-nonspecific component, which is untuned. Both components grow with contrast. Second, we show that a correlation-based intracortical circuit, in which connectivity between cell pairs is determined by the correlation of their LGN inputs, is sufficient to achieve well tuned, contrast-invariant orientation tuning. This circuit generates both spatially opponent, "antiphase" inhibition ("push-pull"), and spatially matched, "same-phase" excitation. The inhibition, if sufficiently strong, suppresses the untuned input component and sharpens responses to the tuned component at all contrasts. The excitation amplifies tuned responses. This circuit agrees with experimental evidence showing spatial opponency between, and similar orientation tuning of, the excitatory and inhibitory inputs received by a simple cell. Orientation tuning is primarily input driven, accounting for the observed invariance of tuning width after removal of intracortical synaptic input, as well as for the dependence of orientation tuning on stimulus spatial frequency. The model differs from previous push-pull models in requiring dominant rather than balanced inhibition and in predicting that a population of layer 4 inhibitory neurons should respond in a contrast-dependent manner to stimuli of all orientations, although their tuning width may be similar to that of excitatory neurons. The model demonstrates that fundamental response properties of cortical layer 4 can be explained by circuitry expected to develop under correlation-based rules of synaptic plasticity, and shows how such circuitry allows the cortex to distinguish stimulus intensity from stimulus form.     

Effect of nitrous oxide on spinal dorsal horn WDR neuronal activity in cats

The effects of nitrous oxide (75%) on the spinal dorsal born wide dynamic range (WDR) neuronal activity were studied in either spinal cord intact or spinal cord-transected cats. Extracellular activity was recorded in the dorsal horn from single WDR neurons responding to noxious and non-noxious stimuli applied to the cutaneous receptive fields on the left bind foot pads of intact or decerebrate, spinal cord-transected (L 1-2) cats. The experiment was divided into four sections as follows: (1) When 10 micrograms of bradykinin (BK) was injected into the femoral artery ipsilateral to the recording site as the noxious test stimulus in the spinal cord-transected cat, all of 6 WDR neurons gave excitatory responses which were not depressed by 75% nitrous oxide. (2) When the injection of 10 micrograms of BK into the femoral artery ipsilateral to the recording site was used in the spinal cord-intact cat, 6 of 15 WDR neurons (40%) gave excitatory responses, which were significantly depressed by 75% nitrous oxide, and 9 of 15 WDR neurons (60%) gave inhibitory responses, which were not affected by 75% nitrous oxide. (3) When 10 micrograms of bradykinin (BK) was injected into the femoral artery contralateral to the recording site as the noxious test stimulus in the spinal cord transected cat, 6 of 12 WDR neurons gave excitatory reasons, which were not depressed by 75% nitrous oxide. (4) When the injection of 10 micrograms of BK into the femoral artery contralateral to the recording site was used in the spinal cord-intact cat, 6 of 6 WDR neurons (100%) gave responses, which were affected by 75% nitrous oxide. We have observed that nitrous oxide reduces the excitation and inhibition of dorsal born WDR neuronal activities induced by BK injection in spinal cord-intact cats, but does not reduce the excitation of those in spinal cord-transected cats. This finding confirmed that the antinociceptive effect of nitrous oxide might be modulated by supraspinal descending inhibitory control systems. In addition our result showed that the supraspinal effect of nitrous oxide was mediated not only by an increase but also a decrease in a supraspinal descending inhibition.     

A parallel noise-robust algorithm to recover depth information from radial flow fields

A parallel algorithm operating on the units ('neurons') of an artificial retina is proposed to recover depth information in a visual scene from radial flow fields induced by ego motion along a given axis. The system consists of up to 600 radii with fewer than 65 radially arranged neurons on each radius. Neurons are connected only to their nearest neighbors, and they are excited as soon as a sufficiently strong gray-level change occurs. The time difference of two subsequently activated neurons is then used by the last-excited neuron to compute the depth information. All algorithmic calculations remain strictly local, and information is exchanged only between adjacent active neurons (except for the final read-out). This, in principle, permits parallel implementation. Furthermore, it is demonstrated that the calculation of the object coordinates requires only a single multiplication with a constant, which is dependent on only the retinal position of the active neuron. The initial restriction to local operations makes the algorithm very noise sensitive. In order to solve this problem, a predication mechanism is introduced. After an object coordinate has been determined, the active neuron computes the time when the next neuronal excitation should take place. This estimated time is transferred to the respective next neuron, which will wait for this excitation only within a certain time window. If the excitation fails to arrive within this window, the previously computed object coordinate is regarded as noisy and discarded. We will show that this predictive mechanism relies also on only a (second) single multiplication with another neuron-dependent constant. Thus, computational complexity remains low, and noisy depth coordinates are efficiently eliminated. Thus, the algorithm is very fast and operates in real time on 128 x 128 images even in a serial implementation on a relatively slow computer. The algorithm is tested on scenes of growing complexity, and a detailed error analysis is provided showing that the depth error remains very low in most cases. A comparison to standard flow-field analysis shows that our algorithm outperforms the older method by far. The analysis of the algorithm also shows that it is generally applicable despite its restrictions, because it is fast and accurate enough such that a complete depth percept can be composed from radial flow field segments. Finally, we suggest how to generalize the algorithm, waiving the restriction of radial flow.     

Vagal, sympathetic and somatic sensory inputs to upper cervical (C1-C3) spinothalamic tract neurons in monkeys

1. Myocardial ischemia activates vagal and sympathetic cardiac afferent fibers. The purpose of this study was to determine a neuro physiological basis for cardiac pain referred to C1-C3 somatic dermatomes. We hypothesized that afferent fibers traveling in vagal or sympathetic nerves transmit nociceptive information to C1-C3 spinothalamic tract (STT) neurons. 2. Electrical stimulation of the left stellate ganglion to excite cardiopulmonary sympathetic afferent fibers increased extracellular activity of 44 of 77 C1-C3 STT neurons examined in 33 anesthetized male monkeys (Macaca fascicularis); responses increased as stimulus strength increased. Additionally, this stimulus inhibited 5 cells, increased/decreased activity of 2 cells, and did not affect 26 cells. 3. Electrical stimulation of the left (ipsilateral) thoracic vagus nerve excited 41 of 78 C1-C3 STT neurons, inhibited 4 neurons, increased/decreased activity of 2 neurons, and did not affect 31 neurons. Responses increased with increasing stimulus strength Contralateral vagal stimulation excited 7 of 39 cells tested, inhibited 4 cells and did not affect 28 cells. 4. Effects of stimulating one or more vagal branches were examined on 22 C1-C3 STT neurons excited by input from left thoracic vagus nerve. Stimulation of the cardiac branch excited 11 of 16 cells tested; stimulation of the recurrent laryngeal nerve excited 11 of 18 cells; stimulation of vagal fibers just rostral to the diaphragm excited 8 of 19 cells. 5. Excitatory somatic receptive fields ranged from small ipsilateral fields to large, sometimes bilateral or noncontinuous fields. Many fields included the ipsilateral neck and/or inferior jaw. Thirty-nine of 74 neurons examined were wide dynamic range (WDR), 21 were high threshold (HT), 6 were low threshold (LT), and 8 did not respond to brushing or noxious pinching of somatic tissues. Most (38 of 39) WDR cells responded to stimulation of the stellate ganglion or vagal fibers, as did 18 of 21 HT cells, 3 of 6 LT cells, and 2 of 8 cells unresponsive to brush or pinch stimuli. 6. Results of this study supported the concept that vagal and/ or sympathetic afferent activation of C1-C3 STT neurons might provide a neural mechanism for referred pain that originates in the heart or other visceral organs but is perceived in the neck and jaw region. Additionally, C1-C3 STT neurons processed sensory information from widespread regions of the body.     

Antisaccade performance predicted by neuronal activity in the supplementary eye field

The voluntary control of gaze implies the ability to make saccadic eye movements specified by abstract instructions, as well as the ability to repress unwanted orientating to sudden stimuli. Both of these abilities are challenged in the antisaccade task, because it requires subjects to look at an unmarked location opposite to a flashed stimulus, without glancing at it. Performance on this task depends on the frontal/prefrontal cortex and related structures, but the neuronal operations underlying antisaccades are not understood. It is not known, for example, how excited visual neurons that normally trigger a saccade to a target (a prosaccade) can activate oculomotor neurons directing gaze in the opposite direction. Visual neurons might, perhaps, alter their receptive fields depending on whether they receive a pro- or antisaccade instruction. If the receptive field is not altered, the antisaccade goal must be computed and imposed from the top down to the appropriate oculomotor neurons. Here we show, using recordings from the supplementary eye field (a frontal cortex oculomotor centre) in monkeys, that visual and movement neurons retain the same spatial selectivity across randomly mixed pro- and antisaccade trials. However, these neurons consistently fire more before antisaccades than prosaccades with the same trajectories, suggesting a mechanism through which voluntary antisaccade commands can override reflexive glances.     

Paroxetine in the treatment of Chinese patients with depressive episode: a double-blind randomized comparison with imipramine

The application of the concept of ray vector fields to optical systems is reexamined. Paraxial or linear optics defines a four-dimensional ray vector field for any optical system: the vector field maps the incident ray vector into the emergent ray vector. In the case of thin systems, including thin astigmatic lenses, one can define a vector field of reduced dimensionality: the vector field is two-dimensional and maps the ray's incident position into the change in reduced direction. When the index of refraction is the same before and after a thin system, the change in reduced direction is the reduced deflection through the system or the reduced prismatic effect. Contrary to what has recently been claimed, this type of two-dimensional vector field does not apply in general to thick systems. However, a number of different types of two-dimensional vector fields can be defined for various particular classes of optical systems. Thick systems differ qualitatively from thin systems. They do not have equivalent thin lenses and cannot generally be replaced by thin lenses. Equations are derived for the change in reduced direction and deflection for a ray through optical systems in general and through separated two- and three-lens systems in particular.