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PubMed2004

Stereoscopic depth magnitude estimation: effects of stimulus spatial frequency and eccentricity.

To determine the effects of stimulus spatial frequency and retinal eccentricity on the perception of depth magnitude derived from disparity cues alone, subjects were asked to estimate the magnitude of depth of a stereoscopically viewed Gabor patch presented to the central or peripheral field with either crossed or uncrossed absolute disparity. Disparity vergence responses to the same Gabor stimuli were separately estimated subjectively by determining the offset required for dichoptic nonius alignment following presentation of the stimulus. The normalized stereoscopic magnitude estimation data generally showed that crossed disparities were perceived with greater depth than uncrossed disparities of the same magnitude, whether presented to the central or peripheral field. Asymmetries in magnitude of depth perception ranged from mild differences between depth directions to complete lack of depth perception for one direction. Disparity vergence response functions varied from (1) appropriate initiation of vergence to both directions of disparity, (2) initiation of vergence to only one direction of disparity, or (3) an attenuated initiation of vergence response to either direction of disparity. Within subjects, their asymmetries in magnitude of depth perception did not correlate with their asymmetries in vergence initiation. The similarity of the asymmetric depth magnitude estimation for a given individual at both stimulus locations tested suggests that common neural mechanisms are responsible for central and peripheral depth magnitude estimation. The lack of correlation between the perceptual and motor responses to the same stimuli suggests that the neural pathways for these responses diverge shortly after the detection of disparity in primary visual cortex.

Adult↗

PubMed2005

Visual attention in behaving cats: attention shifts and sustained attention episodes are accompanied by distinct electrocortical activities.

We analyse a particular class of fast electrocortical rhythms that occur in a limited part of the primary visual cortex (BA 18) during eye saccades in behaving cats placed in a lit environment. Their high frequency (50-132 Hz) contrasts with that of two other classes of rhythms recorded in the same cortical area, the 25-45 Hz visual rhythms (40 Hz) that we previously showed to accompany sustained focused attention, and the alpha rhythms (approximately 10 Hz), that occur in situations of rest. These "very fast visual rhythms" (VFVRs) consist of two brief successive trains, a first one of low amplitude preceding the saccade onset, and a second one, much larger, during the saccade itself. The possibility is considered, that the first train subtends a presaccadic attention shift, and the second, a change of gaze towards a new target through the interception saccade. ECoG activities can thus well distinguish between attention shift and sustained attention.

Animals↗

PubMedDate not supplied

Natural scene statistics and nonlinear neural interactions between frequency-selective mechanisms.

Linear filtering is a basic concept in neural models of early sensory information processing. In particular the visual system has been described to perform a wavelet-like multi-channel decomposition by a set of independent spatial-frequency selective filter mechanisms. Here we suggest that this principle of linear filtering deserves a critical re-evaluation. We propose that an optimal adaptation to natural scene statistics would require AND-like nonlinear interactions between the frequency-selective filter channels. We describe how this hypothesis can be tested by predicted violations of the principle of linearity that should be observable if cortical neurons would actually implement the proposed nonlinearities. We further explain why these effects might have been easily overlooked in earlier tests of the linearity of neurons in primary visual cortex.

Neurons↗

PubMed2005

Strengthening of non-NMDA receptor-dependent horizontal pathways between primary and lateral secondary visual cortices after NMDA receptor-dependent oscillatory neural activities.

Emergence of oscillatory signal flows between the primary visual cortex (Oc1) and medial secondary visual cortex (Oc2M) was previously dynamically demonstrated in rat brain slices by us. Applying caffeine, a neural modulator, to the slices and using optical recording methods revealed this facilitation along horizontal intrinsic pathways in which initial forward propagation from Oc1 to Oc2M was dependent on both N-methyl-D-aspartate receptors (NMDARs) and non-NMDARs. Conversely, oscillatory backward propagation from Oc2M to Oc1 was entirely dependent on NMDARs. The present study examined: (1) whether the signal behavior between Oc1 and lateral secondary visual cortex (Oc2L) is based on the same mechanism with that between Oc1 and Oc2M; and (2) how non-NMDAR and NMDAR activities underlie opening of horizontal corticocortical pathways between Oc1 and Oc2. Under NMDAR blockade, signals elicited in the Oc1 either could not or only weakly penetrated the Oc2L, even in caffeine-containing medium. In contrast, once forward propagation from Oc1 to Oc2L and oscillatory backward propagation from Oc2L to Oc1 was established in caffeine-containing medium, signals elicited in Oc1 could strongly penetrate the Oc2 even during blockade of NMDA activities, when forward penetrating components were dependent on non-NMDARs. These findings suggest that: (1) signal behavior and its mechanism between Oc1and Oc2L are the same with those between Oc1 and Oc2M; and (2) NMDAR activation results in non-NMDAR activity, resulting in opening and strengthening of intrinsic signal pathways between Oc1 and Oc2. NMDAR-dependent forward and backward propagation might be involved in cortical reorganization of the visual cortex.

Animals↗

PubMed2004

Magnetoencephalographic study of occipitotemporal activity elicited by viewing mouth movements.

OBJECTIVE: We studied the temporal and spatial characteristics of neural responses elicited by viewing mouth movements using magnetoencephalography. METHODS: We focused on differences in responses to mouth opening and closing movements by apparent motion, using an averting eyes condition as a control. RESULTS: A large clear MEG component, 1 M (mean peak latency of approximately 160 ms), was elicited by both mouth movements. We modeled the neural sources using a brain electric source analysis (BESA) method and placed the sources around: (1) the occipitotemporal border at human MT/V5, (2) the primary visual cortex (V1), and (3) fusiform gyrus. The calculated activity of Source (1) was large whereas the activity of the others was small or negligible. Source (1), as calculated separately for mouth closing and opening movements and eye movement, showed no significant different amplitude and locations. We did not find any activity in the superior temporal sulcus (STS). CONCLUSIONS: Our results indicate that human MT/V5 is active in the perception of both mouth and eye motions. Viewing mouth and eye movements elicits no significant differences in MT/V5 activity, indicating that the perception of movement of facial parts is probably processed in the same manner. SIGNIFICANCE: Characteristic activities in the human MT/V5 elicited by viewing mouth movement were clarified by MEG.

Adult↗

PubMed2003

Motion processing: how low can you go?

Neurons at early stages in the visual system can only 'view' small parts of the visual world, impeding their ability to determine correctly an object's motion direction. New studies suggest that this 'aperture problem' is already solved by special neurons at the first stage of motion detection in primary visual cortex.

Humans↗

PubMed2004

Magnetic stimulation of extrastriate body area impairs visual processing of nonfacial body parts.

Functional magnetic resonance imaging indicates that observation of the human body induces a selective activation of a lateral occipitotemporal cortical area called extrastriate body area (EBA). This area is responsive to static and moving images of the human body and parts of it, but it is insensitive to faces and stimulus categories unrelated to the human body. With event-related repetitive transcranial magnetic stimulation, we tested the possible causal relation between neural activity in EBA and visual processing of body-related, nonfacial stimuli. Facial and noncorporeal stimuli were used as a control. Interference with neural activity in EBA induced a clear impairment, consisting of a significant increase in discriminative reaction time, in the visual processing of body parts. The effect was selective for stimulus type, because it affected responses to nonfacial body stimuli but not to noncorporeal and facial stimuli, and for locus of stimulation, because the effect from the interfering stimulation of EBA was absent during a corresponding stimulation of primary visual cortex. The results provide strong evidence that neural activity in EBA is not only correlated with but also causally involved in the visual processing of the human body and its parts, except the face.

Adult↗

PubMed2005

Saccades differentially modulate human LGN and V1 responses in the presence and absence of visual stimulation.

Saccades occur several times each second in normal human vision. The visual image moves across the retina at high velocity during a saccade, yet no blurring of the visual scene is perceived . Active suppression of visual input may account for this perceptual continuity, but the neural mechanisms underlying such saccadic suppression remain unclear. We used functional MRI to specifically examine responses in the lateral geniculate nucleus (LGN) and primary visual cortex (V1) during saccades. Activity in both V1 and LGN was strongly modulated by saccades. Furthermore, this modulation depended on whether visual stimulation was present or absent. In complete darkness, saccades led to reliable signal increases in V1 and LGN, whereas in the presence of visual stimulation, saccades led to suppression of visually evoked responses. These findings represent unequivocal evidence for saccadic suppression in human LGN and retinotopically defined V1 and are consistent with the earliest site of saccadic suppression lying at or before V1.

Geniculate Bodies↗

PubMed2006

Contrast invariance in the human lateral occipital complex depends on attention.

The human visual system has a remarkable ability to successfully operate under a variety of challenging viewing conditions. For example, our object-recognition capabilities are largely unaffected by low-contrast (e.g., foggy) environments. The basis for this ability appears to be reflected in the neural responses in higher cortical visual areas that have been characterized as being invariant to changes in luminance contrast: neurons in these areas respond nearly equally to low-contrast as compared to high-contrast stimuli. This response pattern is fundamentally different than that observed in earlier visual areas such as primary visual cortex (V1), which is highly dependent on contrast. How this invariance is achieved in higher visual areas is largely unknown. We hypothesized that directed spatial attention is an important prerequisite of the contrast-invariant responses in higher visual areas and tested this with functional MRI (fMRI) while subjects directed their attention either toward or away from contrast-varying shape stimuli. We found that in the lateral occipital complex (LOC), a visual area important for processing shape information, attention changes the form of the contrast response function (CRF). By directing attention away from the shape stimuli, the CRF in the LOC was similar to that measured in V1. We describe a number of mechanisms that could account for this important function of attention.

Adult↗

PubMed2006

Visual physiology: perceived size looms large.

Visual illusions tell us that size perception depends heavily upon complex contextual cues, often thought to be extracted by brain areas high in the visual hierarchy. Now, a new study shows that perceived size is reflected in activity as early as the primary visual cortex.

Humans↗

PubMed2026

Retinal microstructural alterations as early phenotypes of depression in radiogenomics analysis.

BACKGROUND: With the increasing prevalence of depression, there is an urgent clinical need for early screening in depression. The retina offers a promising window for early screening in depression due to its rapid, non-invasive, objective, eye-brain correlated characteristics, but previous research has yielded conflicting alterations in retinal microstructure in depression. METHODS: We screened retinal optical coherence tomography and brain magnetic resonance imaging data in the UK Biobank to enroll 23,225 participants for retinal study of depression occurrence, and 1475 participants for the eye-brain association study. We also used genetic data (ID: ebi-a-GCST90014267 and ukb-d-20,448) from the Integrative Epidemiology Unit Open Genome-Wide Association Study for Mendelian randomization analysis. We used Cox regression to assess the association between retinal microstructure and depression risk, Mendelian randomization to infer causality, and mediation analysis to explore retina-brain pathway association. RESULTS: The Cox regression analysis showed that retinal ganglion cell-inner plexiform layer (GCIPL) thickness remained a significant predictor of depression. The Mendelian randomization analysis indicated a positive statistical association between GCIPL thickness and depression. Moreover, there was a significant positive correlation (all p < 0.001) between the volume of specific depression-related brain regions and the GCIPL thickness. Adjusting for age, sex, and head size, the mediation analysis provided preliminary evidence for a potential anatomical pathway linking retinal GCIPL thickness to depression-related brain regions through primary visual cortex and secondary visual cortex volumes. CONCLUSION: Thickened retinal GCIPL is a potential early phenotype of depression and has a potential association pathway with depression-related brain regions using a radiogenomics approach.

Humans↗

PubMed2004

In vitro autoradiographic localization of calcitonin and amylin binding sites in monkey brain.

Calcitonin (CT) and amylin are related peptides with potent central actions, including suppression of appetite and gastric acid secretion. Little is known about the distribution and binding characteristics of amylin receptors in species other than rat; therefore, in this study, by using in vitro autoradiography, we have mapped the distribution of 125I-rat amylin binding sites in the monkey brain and compared this distribution to that of binding sites for 125I-salmon CT (125I-sCT). Highest densities of 125I-amylin binding were in the hypothalamus, including the arcuate nucleus and parts of the ventromedial hypothalamic nuclei, and the solitary nucleus. Rostrally, moderate to high density binding was present in parts of the preoptic area, bed nucleus of the stria terminalis, amygdala and accumbens nucleus (Acb). Caudally, binding of amylin was more restricted, with moderate to high density binding present only in dorsal raphe, and area postrema. The primary visual cortex displayed strong and periodic CT binding in layer 4. The subcortical pattern of distribution of amylin and CT receptors in the monkey was similar to that seen previously in the rat, although the relative densities of binding to different brain structures were not always conserved. As with rat, monkey amylin receptors were a subset of the sites labeled with 125I-sCT. Analysis of receptor specificity indicated a greater relative potency of CT peptides in competing for 125I-amylin binding in monkey, when compared to rat, while, there was a decrease in the relative potency of CT gene-related peptides, potentially due to differences the level of receptor activity modifying proteins (RAMPs) in monkey versus rat brain. Amylin receptors in primates are likely to perform a similar role to those in rats; however, the interaction of the receptors with related peptides may differ.

Amyloid↗

PubMed2004

Coding with noisy neurons: stability of tuning curve estimation strongly depends on the analysis method.

An important issue in the neurosciences is a quantitative description of the relation between sensory stimuli presented to an animal and their representations in the nervous system. A standard technique is the construction of a neural tuning curve, that is, a neuron's average firing rate as a function of some parameter characterizing a family of stimuli. It is unavoidable that some of the response data are erroneously attributed to a cell, e.g., during spike sorting. However, the widely used method of statistical analysis based on the sample mean and least-squares approximation for the spike count can perform extremely badly if the noise distribution is not exactly normal, which is almost never the case in applications. Here, we present a method for constructing neural tuning curves that is especially suited for cases of high noise and the presence of outliers. Since it is usually not decidable if an outlier is faulty or not we limit the influence of far outlying points rather than try to identify and discard them. In contrast to traditional methods employing a point-by-point estimation of a tuning curve, we use all measured data from all different stimulus conditions at once in the construction. Given the measured data at only a finite number of stimulus conditions, a robust tuning curve is obtained that approximates the cell's ideal tuning curve optimally in all stimulus conditions with respect to a given distance measure. A measure that assesses the quality of this fitting method with respect to the traditional least-squares fitting method and to a median-based fitting method is introduced. The reliability of inference with respect to the encoding accuracy that can be achieved by a population of neurons is demonstrated in both artificially generated and experimentally recorded data from rat primary visual cortex. While the data shown in this paper are responses to orientation stimuli, the method of tuning curve construction is also viable and maintains its optimality properties for the case in which the stimulus is defined on a finite interval.

Action Potentials↗

PubMed2005

Extraction of the average and differential dynamical response in stimulus-locked experimental data.

In optical imaging experiments of primary visual cortex, visual stimuli evoke a complicated dynamics. Typically, any stimulus with sufficient contrast evokes a response. Much of the response is the same regardless of which stimulus is presented. For instance, when oriented drifting gratings are presented to the visual system, over 90% of the response is the same from orientation to orientation. Small differences may be seen, however, between the responses to different orientations. A problem in the analysis of optical measurements of the response to stimulus in cortical tissue is the distinction of the 'global' or 'non-specific' response from the 'differential' or 'stimulus-specific' response. This problem arises whenever the signal of interest is the difference in response to various stimuli and is evident in many kinds of uni- and multivariate data. To this end, we present enhancements to a frequency-based method that we previously introduced called the periodic stacking method. These enhancements allow us to separately estimate the dynamics of both the average signal across all stimuli (the 'global' response) and deviations from the average amongst the various stimuli (the 'stimulus-specific' response) evoked in response to a set of stimuli. We also discuss improvements in the signal-to-noise ratio, relative to standard trial averaging methods, that result from the data-adaptive smoothing in our method.

Animals↗

PubMed2005

Air-driven eye shutter system for vision experiments using awake behaving animals.

When conducting physiological and behavioral experiments for vision research, we often need to present stimuli monocularly. In this report, we describe a new eye shutter system that was developed to occlude individual eyes during experiments with awake behaving animals. The eye of choice is occluded by an air pressure-driven opaque mask, the opening and closing of which is controlled by computer. This new eye shutter system has several advantages over other systems: (1) it can completely shield the eye from light using a physically opaque eye mask; (2) contamination of electrophysiological recordings by electrical noise is avoided because the actuator is not electrical; (3) the left and right eyes can be randomly occluded in each trial; (4) space for apparatus in front of the animal's face is not required. We used this eye shutter system to record neural activity from the primary visual cortex of awake monkeys and confirmed that this system is suitable for the monocular presentation of visual stimuli during electrophysiological recordings from awake animals.

Air↗

PubMed2004

Electrophysiological correlates of associative visual agnosia lesioned in the ventral pathway.

Visual agnosia has been well studied by anatomical, neuropsychological and neuroimaging studies. However, functional changes in the brain have been rarely assessed by electrophysiological methods. We carried out electrophysiological examinations on a 23-year-old man with associative visual agnosia, prosopagnosia and cerebral achromatopsia to evaluate the higher brain dysfunctions of visual recognition. Electrophysiological methods consisted of achromatic, chromatic and category-specific visual evoked potentials (CS-VEPs), and event-related potentials (ERPs) with color and motion discrimination tasks. Brain magnetic resonance imaging revealed large white matter lesions in the bilateral temporo-occipital lobes involving the lingual and fusiform gyri (V4) and inferior longitudinal fasciculi due to multiple sclerosis. Examinations including CS-VEPs demonstrated dysfunctions of face and object perception while sparing semantic word perception after primary visual cortex (V1) in the ventral pathway. ERPs showed abnormal color perception in the ventral pathway with normal motion perception in the dorsal pathway. These electrophysiological findings were consistent with lesions in the ventral pathway that were detected by clinical and neuroimaging findings. Therefore, CS-VEPs and ERPs with color and motion discrimination tasks are useful methods for assessing the functional changes of visual recognition such as visual agnosia.

Adult↗

PubMedDate not supplied

Reaching beyond the classical receptive field of V1 neurons: horizontal or feedback axons?

It is commonly assumed that the orientation-selective surround field of neurons in primary visual cortex (V1) is due to interactions provided solely by intrinsic long-range horizontal connections. We review evidence for and against this proposition and conclude that horizontal connections are too slow and cover too little visual field to subserve all the functions of suppressive surrounds of V1 neurons in the macaque monkey. We show that the extent of visual space covered by horizontal connections corresponds to the region of low contrast summation of the receptive field center mechanism. This region encompasses the classically defined receptive field center and the proximal surround. Beyond this region, feedback connections are the most likely substrate for surround suppression. We present evidence that inactivation of higher order areas leads to a major decrease in the strength of the suppressive surround of neurons in lower order areas, supporting the hypothesis that feedback connections play a major role in center-surround interactions.

Animals↗

PubMedDate not supplied

Biological computation of image motion from flows over boundaries.

A theory of early motion processing in the human and primate visual system is presented which is based on the idea that spatio-temporal retinal image data is represented in primary visual cortex by a truncated 3D Taylor expansion that we refer to as a jet vector. This representation allows all the concepts of differential geometry to be applied to the analysis of visual information processing. We show in particular how the generalised Stokes theorem can be used to move from the calculation of derivatives of image brightness at a point to the calculation of image brightness differences on the boundary of a volume in space-time and how this can be generalised to apply to integrals of products of derivatives. We also provide novel interpretations of the roles of direction selective, bi-directional and pan-directional cells and of type I and type II cells in V5/MT.

Animals↗