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Geniculate Nucleus (geniculate + nucleus)
Kinds of Geniculate Nucleus Selected AbstractsThe Developmental Remodeling of Eye-Specific Afferents in the Ferret Dorsal Lateral Geniculate NucleusTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 1 2010Colenso M. Speer Abstract Eye-specific projections to the dorsal lateral geniculate nucleus (dLGN) serve as a model for exploring how precise patterns of circuitry form during development in the mammalian central nervous system. Using a combination of dual-label anterograde retinogeniculate tracing and Nissl-staining, we studied the patterns of eye-specific afferents and cellular laminae in the dLGN of the pigmented sable ferret at eight developmental timepoints between birth and adulthood. Each time point was investigated in the three standard orthogonal planes of section, allowing us to generate a complete anatomical map of eye-specific development in this species. We find that eye-specific retinal ganglion cell axon segregation varies according to location in the dLGN, with the principle contralateral (A) and ipsilateral layers (A1) maturing first, followed by the contralateral and ipsilateral C laminae. Cytoarchitectural lamination lags behind eye-specific segregation, except in the C laminae where underlying cellular layers never develop to accompany eye-specific afferent domains. The emergence of On/Off sublaminae occurs following eye-specific segregation in this species. On the basis of these findings, we constructed a three-dimensional map of eye-specific channels in the developing and mature ferret dLGN. Anat Rec, 293:1,24, 2010. © 2010 Wiley-Liss, Inc. [source] Neural recognition molecule NB-2 of the contactin/F3 subgroup in rat: Specificity in neurite outgrowth-promoting activity and restricted expression in the brain regionsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2001Junko Ogawa Abstract NB-2, a neural cell recognition molecule of the contactin/F3 subgroup, promoted neurite outgrowth of the cerebral cortical neurons but not the hippocampal neurons. NB-2 in rat became apparent after birth at protein level, reaching a maximum at postnatal day 14 in the cerebrum and postnatal day 3 in the cerebellum. NB-2 in the cerebellum declined abruptly thereafter. In situ hybridization demonstrated that NB-2 mRNA was highly expressed in regions implicated in the central auditory pathway, including the cochlear nuclei, superior olive, inferior colliculi, medial geniculate nuclei, and auditory cortex. In addition, a high level of NB-2 expression was observed in the accessory olfactory bulb, thalamic nuclei, facial nucleus, and inferior olive. By immunohistochemistry, intense immunoreactivity against NB-2 was also detected in the auditory pathway. Thus, NB-2 is expressed in highly restricted brain regions, including the auditory system, suggesting that it plays specific roles in the development and/or maturation of the regions. J. Neurosci. Res. 65:100,110, 2001. © 2001 Wiley-Liss, Inc. [source] Afferent projections to nucleus reuniens of the thalamusTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 2 2004James Timothy McKenna Abstract The nucleus reuniens (RE) is the largest of the midline nuclei of the thalamus and the major source of thalamic afferents to the hippocampus and parahippocampal structures. Nucleus reuniens has recently been shown to exert powerful excitatory actions on CA1 of the hippocampus. Few reports on any species have examined afferent projections to nucleus reuniens. By using the retrograde anatomical tracer Fluorogold, we examined patterns of afferent projections to RE in the rat. We showed that RE receives a diverse and widely distributed set of afferents projections. The main sources of input to nucleus reuniens were from the orbitomedial, insular, ectorhinal, perirhinal, and retrosplenial cortices; CA1/subiculum of hippocampus; claustrum, tania tecta, lateral septum, substantia innominata, and medial and lateral preoptic nuclei of the basal forebrain; medial nucleus of amygdala; paraventricular and lateral geniculate nuclei of the thalamus; zona incerta; anterior, ventromedial, lateral, posterior, supramammillary, and dorsal premammillary nuclei of the hypothalamus; and ventral tegmental area, periaqueductal gray, medial and posterior pretectal nuclei, superior colliculus, precommissural/commissural nuclei, nucleus of the posterior commissure, parabrachial nucleus, laterodorsal and pedunculopontine tegmental nuclei, nucleus incertus, and dorsal and median raphe nuclei of the brainstem. The present findings of widespread projections to RE, mainly from limbic/limbic-associated structures, suggest that nucleus reuniens represents a critical relay in the transfer of limbic information (emotional/cognitive) from RE to its major targets, namely, to the hippocampus and orbitomedial prefrontal cortex. RE appears to be a major link in the two-way exchange of information between the hippocampus and the medial prefrontal cortex. J. Comp. Neurol. 480:115,142, 2004. © 2004 Wiley-Liss, Inc. [source] The magnocellular theory of developmental dyslexiaDYSLEXIA, Issue 1 2001John Stein Abstract Low literacy is termed ,developmental dyslexia' when reading is significantly behind that expected from the intelligence quotient (IQ) in the presence of other symptoms,incoordination, left,right confusions, poor sequencing,that characterize it as a neurological syndrome. 5,10% of children, particularly boys, are found to be dyslexic. Reading requires the acquisition of good orthographic skills for recognising the visual form of words which allows one to access their meaning directly. It also requires the development of good phonological skills for sounding out unfamiliar words using knowledge of letter sound conversion rules. In the dyslexic brain, temporoparietal language areas on the two sides are symmetrical without the normal left-sided advantage. Also brain ,warts' (ectopias) are found, particularly clustered round the left temporoparietal language areas. The visual magnocellular system is responsible for timing visual events when reading. It therefore signals any visual motion that occurs if unintended movements lead to images moving off the fovea (,retinal slip'). These signals are then used to bring the eyes back on target. Thus, sensitivity to visual motion seems to help determine how well orthographic skill can develop in both good and bad readers. In dyslexics, the development of the visual magnocellular system is impaired: development of the magnocellular layers of the dyslexic lateral geniculate nucleus (LGN) is abnormal; their motion sensitivity is reduced; many dyslexics show unsteady binocular fixation; hence poor visual localization, particularly on the left side (left neglect). Dyslexics' binocular instability and visual perceptual instability, therefore, can cause the letters they are trying to read to appear to move around and cross over each other. Hence, blanking one eye (monocular occlusion) can improve reading. Thus, good magnocellular function is essential for high motion sensitivity and stable binocular fixation, hence proper development of orthographic skills. Many dyslexics also have auditory/phonological problems. Distinguishing letter sounds depends on picking up the changes in sound frequency and amplitude that characterize them. Thus, high frequency (FM) and amplitude modulation (AM) sensitivity helps the development of good phonological skill, and low sensitivity impedes the acquisition of these skills. Thus dyslexics' sensitivity to FM and AM is significantly lower than that of good readers and this explains their problems with phonology. The cerebellum is the head ganglion of magnocellular systems; it contributes to binocular fixation and to inner speech for sounding out words, and it is clearly defective in dyslexics. Thus, there is evidence that most reading problems have a fundamental sensorimotor cause. But why do magnocellular systems fail to develop properly? There is a clear genetic basis for impaired development of magnocells throughout the brain. The best understood linkage is to the region of the Major Histocompatibility Complex (MHC) Class 1 on the short arm of chromosome 6 which helps to control the production of antibodies. The development of magnocells may be impaired by autoantibodies affecting the developing brain. Magnocells also need high amounts of polyunsaturated fatty acids to preserve the membrane flexibility that permits the rapid conformational changes of channel proteins which underlie their transient sensitivity. But the genes that underlie magnocellular weakness would not be so common unless there were compensating advantages to dyslexia. In developmental dyslexics there may be heightened development of parvocellular systems that underlie their holistic, artistic, ,seeing the whole picture' and entrepreneurial talents. Copyright © 2001 John Wiley & Sons, Ltd. [source] Serum or target deprivation-induced neuronal death causes oxidative neuronal accumulation of Zn2+ and loss of NAD+EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2010Christian T. Sheline Abstract Trophic deprivation-mediated neuronal death is important during development, after acute brain or nerve trauma, and in neurodegeneration. Serum deprivation (SD) approximates trophic deprivation in vitro, and an in vivo model is provided by neuronal death in the mouse dorsal lateral geniculate nucleus (LGNd) after ablation of the visual cortex (VCA). Oxidant-induced intracellular Zn2+ release ([Zn2+]i) from metallothionein-3 (MT-III), mitochondria or ,protein Zn2+', was implicated in trophic deprivation neurotoxicity. We have previously shown that neurotoxicity of extracellular Zn2+ required entry, increased [Zn2+]i, and reduction of NAD+ and ATP levels causing inhibition of glycolysis and cellular metabolism. Exogenous NAD+ and sirtuin inhibition attenuated Zn2+ neurotoxicity. Here we show that: (1) Zn2+ is released intracellularly after oxidant and SD injuries, and that sensitivity to these injuries is proportional to neuronal Zn2+ content; (2) NAD+ loss is involved , restoration of NAD+ using exogenous NAD+, pyruvate or nicotinamide attenuated these injuries, and potentiation of NAD+ loss potentiated injury; (3) neurons from genetically modified mouse strains which reduce intracellular Zn2+ content (MT-III knockout), reduce NAD+ catabolism (PARP-1 knockout) or increase expression of an NAD+ synthetic enzyme (Wlds) each had attenuated SD and oxidant neurotoxicities; (4) sirtuin inhibitors attenuated and sirtuin activators potentiated these neurotoxicities; (5) visual cortex ablation (VCA) induces Zn2+ staining and death only in ipsilateral LGNd neurons, and a 1 mg/kg Zn2+ diet attenuated injury; and finally (6) NAD+ synthesis and levels are involved given that LGNd neuronal death after VCA was dramatically reduced in Wlds animals, and by intraperitoneal pyr vate or nicotinamide. Zn2+ toxicity is involved in serum and trophic deprivation-induced neuronal death. [source] Color responses of the human lateral geniculate nucleus: selective amplification of S-cone signals between the lateral geniculate nucleno and primary visual cortex measured with high-field fMRIEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2008Kathy T. Mullen Abstract The lateral geniculate nucleus (LGN) is the primary thalamic nucleus that relays visual information from the retina to the primary visual cortex (V1) and has been extensively studied in non-human primates. A key feature of the LGN is the segregation of retinal inputs into different cellular layers characterized by their differential responses to red-green (RG) color (L/M opponent), blue-yellow (BY) color (S-cone opponent) and achromatic (Ach) contrast. In this study we use high-field functional magnetic resonance imaging (4 tesla, 3.6 × 3.6 × 3 mm3) to record simultaneously the responses of the human LGN and V1 to chromatic and Ach contrast to investigate the LGN responses to color, and how these are modified as information transfers between LGN and cortex. We find that the LGN has a robust response to RG color contrast, equal to or greater than the Ach response, but a significantly poorer sensitivity to BY contrast. In V1 at low temporal rates (2 Hz), however, the sensitivity of the BY color pathway is selectively enhanced, rising in relation to the RG and Ach responses. We find that this effect generalizes across different stimulus contrasts and spatial stimuli (1-d and 2-d patterns), but is selective for temporal frequency, as it is not found for stimuli at 8 Hz. While the mechanism of this cortical enhancement of BY color vision and its dynamic component is unknown, its role may be to compensate for a weak BY signal originating from the sparse distribution of neurons in the retina and LGN. [source] Drifting grating stimulation reveals particular activation properties of visual neurons in the caudate nucleusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2008Attila Nagy Abstract The role of the caudate nucleus (CN) in motor control has been widely studied. Less attention has been paid to the dynamics of visual feedback in motor actions, which is a relevant function of the basal ganglia during the control of eye and body movements. We therefore set out to analyse the visual information processing of neurons in the feline CN. Extracellular single-unit recordings were performed in the CN, where the neuronal responses to drifting gratings of various spatial and temporal frequencies were recorded. The responses of the CN neurons were modulated by the temporal frequency of the grating. The CN units responded optimally to gratings of low spatial frequencies and exhibited low spatial resolution and fine spatial frequency tuning. By contrast, the CN neurons preferred high temporal frequencies, and exhibited high temporal resolution and fine temporal frequency tuning. The spatial and temporal visual properties of the CN neurons enable them to act as spatiotemporal filters. These properties are similar to those observed in certain feline extrageniculate visual structures, i.e. in the superior colliculus, the suprageniculate nucleus and the anterior ectosylvian cortex, but differ strongly from those of the primary visual cortex and the lateral geniculate nucleus. Accordingly, our results suggest a functional relationship of the CN to the extrageniculate tecto-thalamo-cortical system. This system of the mammalian brain may be involved in motion detection, especially in velocity analysis of moving objects, facilitating the detection of changes during the animal's movement. [source] Depression of retinogeniculate synaptic transmission by presynaptic D2 -like dopamine receptors in rat lateral geniculate nucleusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2006G. Govindaiah Abstract Extraretinal projections onto neurons in the dorsal lateral geniculate nucleus (dLGN) play an important role in modifying sensory information as it is relayed from the visual thalamus to neocortex. The dLGN receives dopaminergic innervation from the ventral tegmental area; however, the role of dopamine in synaptic transmission in dLGN has not been explored. In the present study, whole cell recordings were obtained to examine the actions of dopamine on glutamatergic synaptic transmission. Dopamine (2,100 µm) strongly suppressed excitatory synaptic transmission in dLGN relay neurons that was evoked by optic tract stimulation and mediated by both N -methyl- d -aspartate and non -N -methyl- d -aspartate glutamate receptors. In contrast, dopamine did not alter inhibitory synaptic transmission arising from either dLGN interneurons or thalamic reticular nucleus neurons. The suppressive action of dopamine on excitatory synaptic transmission was mimicked by the D2 -like dopamine receptor agonist bromocriptine (2,25 µm) but not by the D1 -like receptor agonist SKF38393 (10,25 µm). In addition, the dopamine-mediated suppression was antagonized by the D2 -like receptor antagonist sulpiride (10,20 µm) but not by the D1 -like receptor antagonist SCH23390 (5,25 µm). The dopamine-mediated decrease in evoked excitatory postsynaptic current amplitude was accompanied by an increase in the magnitude of paired-pulse depression. Furthermore, dopamine also reduced the frequency but not the amplitude of miniature excitatory postsynaptic currents. Taken together, these data suggest that dopamine may act presynaptically to regulate the release of glutamate at the retinogeniculate synapse and modify transmission of visual information in the dLGN. [source] Auditory activation of ,visual' cortical areas in the blind mole rat (Spalax ehrenbergi)EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2002Gilles Bronchti Abstract The mole rat (Spalax ehrenbergi) is a subterranean rodent whose adaptations to its fossorial life include an extremely reduced peripheral visual system and an auditory system suited for the perception of vibratory stimuli. We have previously shown that in this blind rodent the dorsal lateral geniculate nucleus, the primary visual thalamic nucleus of sighted mammals, is activated by auditory stimuli. In this report we focus on the manifestation of this cross-modal compensation at the cortical level. Cyto- and myeloarchitectural analyses of the occipital area showed that despite the almost total blindness of the mole rat this area has retained the organization of a typical mammalian primary visual cortex. Application of the metabolic marker 2-deoxyglucose and electrophysiological recording of evoked field potentials and single-unit activity disclosed that a considerable part of this area is activated by auditory stimuli. Previous neuronal tracing studies had revealed the origin of the bulk of this auditory input to be the dorsal lateral geniculate nucleus which itself receives auditory input from the inferior colliculus. [source] Neural selectivity for hue and saturation of colour in the primary visual cortex of the monkeyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2000Akitoshi Hanazawa Abstract In the inferior temporal (IT) cortex of monkeys, which has been shown to play a critical role in colour discrimination, there are neurons sensitive to a narrow range of hues and saturation. By contrast, neurons in the retina and the parvocellular layer of the lateral geniculate nucleus (pLGN) encode colours in a way that does not provide explicit representation of hue or saturation, and the process by which hue- and saturation-selectivity is elaborated remains unknown. We therefore tested the colour-selectivity of neurons in the primary visual cortex (V1) and compared it with those of pLGN and IT neurons. Quantitative analysis was performed using a standard set of colours, systematically distributed within the CIE (Commission Internationale de l'Eclairage)-xy chromaticity diagram. Selectivity for hue and saturation was characterized by analysing response contours reflecting the overall distribution of responses across the chromaticity diagram. We found that the response contours of almost all pLGN neurons were linear and broadly tuned for hue. Many V1 neurons behaved similarly; nonetheless, a considerable number of V1 neurons had clearly curved response contours and were selective for a narrow range of hues or saturation. The relative frequencies of neurons exhibiting various selectivities for hue and saturation were remarkably similar in the V1 and IT cortex, but were clearly different in the pLGN. Thus, V1 apparently plays a very important role in the conversion of colour signals necessary for generating the elaborate colour selectivity observed in the IT cortex. [source] Visual response augmentation in cat (and macaque) LGN: potentiation by corticofugally mediated gain control in the temporal domainEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2000Javier Cudeiro Abstract Visual responses of neurons are dependent on the context of a stimulus, not only in spatial terms but also temporally, although evidence for temporally separate visual influences is meagre, based mainly on studies in the higher cortex. Here we demonstrate temporally induced elevation of visual responsiveness in cells in the lateral geniculate nucleus (LGN) of cat and monkey following a period of high intensity (elevated contrast) stimulation. This augmentation is seen in 40,70% (monkey,cat) of cells tested and of all subtypes. Peaking at ,,3 min following the period of intense stimulation, it can last for 10,12 min and can be repeated and summed in time. Furthermore, it is dependent on corticofugal input, is seen even when high contrast stimuli of orthogonal orientation are used and therefore results from a/any prior increase in activity in the retino-geniculo-striate pathway. We suggest that this reflects a general mechanism for control of visual responsiveness; both a flexible and dynamic means of changing effectiveness of thalamic activity as visual input changes, but also a mechanism which is an emergent property of the thalamo-cortico-thalamic loop. [source] Optic radiation changes after optic neuritis detected by tractography-based group mappingHUMAN BRAIN MAPPING, Issue 3 2005Olga Ciccarelli Abstract Postmortem data suggest that trans-synaptic degeneration occurs in the lateral geniculate nucleus after optic nerve injury. This study investigated in vivo the optic radiations in patients affected by optic neuritis using fast marching tractography (FMT), a diffusion magnetic resonance imaging (MRI) fiber tracking method, and group mapping techniques, which allow statistical comparisons between subjects. Seven patients, 1 year after isolated unilateral optic neuritis, and ten age and gender-matched controls underwent whole-brain diffusion tensor MR imaging. The FMT algorithm was used to generate voxel-scale connectivity (VSC) maps in the optic radiations in each subject in native space. Group maps of the left and right optic radiations were created in the patient and control group in a standardized reference frame using statistical parametric mapping (SPM99). The reconstructed optic radiations in the patient group were localized more laterally in the posterior part of the tracts and more inferiorly than in the control group. Patients showed reduced VSC values in both tracts compared with controls. These findings suggest that the group mapping techniques might be used to assess changes in the optic radiations in patients after an episode of optic neuritis. The changes we have observed may be secondary to the optic nerve damage. Hum Brain Mapp, 2005. © 2005 Wiley-Liss, Inc. [source] Neurogenic development of the visual areas in the Chinese softshell turtle (Pelodiscus sinensis) and evolutionary implicationsJOURNAL OF ANATOMY, Issue 5 2008Chao Xi Abstract To characterize the neurogenic development of the visual areas of the turtle (Pelodiscus sinensis) during embryogenesis, a single dose of [3H]-thymidine (10 µCi) was injected into egg yolks from stages S11~12 to S21. At hatching, localization of [3H]-thymidine incorporation was examined, and led to three main observations. (1) Neurogenesis occurred in the stratum griseum centrale of the tectum opticum from S11~12 to S16 with a peak at S12. No obvious gradients of neurogenesis were observed. (2) Neurogenesis in the nucleus rotundus (Rot) and in the dorsal lateral geniculate nucleus (GLd) occurred from S11~12 to S15. Gradients of neurogenesis were detected along ventral,dorsal and lateral,medial axes in the Rot, but only the latter neurogenic gradient occurred in the GLd. (3) In the visual region of the dorsal ventricular ridge, neurogenesis lasted from S11~12 to S16. Similarly, neurogenesis occurred from S11~12 to S16~17 in the dorsal cortex, with a peak at S12 for both telencephalic visual regions. Neurogenesis followed a ventrolateral to dorsomedial gradient in the visual region of the dorsal ventricular ridge, and a superficial to deep gradient in the caudal dorsal cortex. A significant number of neurons in the rostral dorsal cortex followed a deep (earlier arising) to superficial (later arising) pattern of neurogenesis, similar to that in the avian Wulst or in the mammalian isocortex. Finally, we compared the timing and development of neurogenesis in the turtle with birds and mammals to understand the evolutionary implications of these processes. [source] The Developmental Remodeling of Eye-Specific Afferents in the Ferret Dorsal Lateral Geniculate NucleusTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 1 2010Colenso M. Speer Abstract Eye-specific projections to the dorsal lateral geniculate nucleus (dLGN) serve as a model for exploring how precise patterns of circuitry form during development in the mammalian central nervous system. Using a combination of dual-label anterograde retinogeniculate tracing and Nissl-staining, we studied the patterns of eye-specific afferents and cellular laminae in the dLGN of the pigmented sable ferret at eight developmental timepoints between birth and adulthood. Each time point was investigated in the three standard orthogonal planes of section, allowing us to generate a complete anatomical map of eye-specific development in this species. We find that eye-specific retinal ganglion cell axon segregation varies according to location in the dLGN, with the principle contralateral (A) and ipsilateral layers (A1) maturing first, followed by the contralateral and ipsilateral C laminae. Cytoarchitectural lamination lags behind eye-specific segregation, except in the C laminae where underlying cellular layers never develop to accompany eye-specific afferent domains. The emergence of On/Off sublaminae occurs following eye-specific segregation in this species. On the basis of these findings, we constructed a three-dimensional map of eye-specific channels in the developing and mature ferret dLGN. Anat Rec, 293:1,24, 2010. © 2010 Wiley-Liss, Inc. [source] Somatosensory Nuclei of the Manatee Brainstem and ThalamusTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 9 2007Diana K. Sarko Abstract Florida manatees have an extensive, well-developed system of vibrissae distributed over their entire bodies and especially concentrated on the face. Although behavioral and anatomical assessments support the manatee's reliance on somatosensation, a systematic analysis of the manatee thalamus and brainstem areas dedicated to tactile input has never been completed. Using histochemical and histological techniques (including stains for myelin, Nissl, cytochrome oxidase, and acetylcholinesterase), we characterized the relative size, extent, and specializations of somatosensory regions of the brainstem and thalamus. The principal somatosensory regions of the brainstem (trigeminal, cuneate, gracile, and Bischoff's nucleus) and the thalamus (ventroposterior nucleus) were disproportionately large relative to nuclei dedicated to other sensory modalities, providing neuroanatomical evidence that supports the manatee's reliance on somatosensation. In fact, areas of the thalamus related to somatosensation (the ventroposterior and posterior nuclei) and audition (the medial geniculate nucleus) appeared to displace the lateral geniculate nucleus dedicated to the subordinate visual modality. Furthermore, it is noteworthy that, although the manatee cortex contains Rindenkerne (barrel-like cortical nuclei located in layer VI), no corresponding cell clusters were located in the brainstem ("barrelettes") or thalamus ("barreloids"). Anat Rec, 290:1138,1165, 2007. © 2007 Wiley-Liss, Inc. [source] Chromatic and spatial properties of parvocellular cells in the lateral geniculate nucleus of the marmoset (Callithrix jacchus)THE JOURNAL OF PHYSIOLOGY, Issue 1 2004Esther M. Blessing The parvocellular (PC) division of the afferent visual pathway is considered to carry neuronal signals which underlie the red,green dimension of colour vision as well as high-resolution spatial vision. In order to understand the origin of these signals, and the way in which they are combined, the responses of PC cells in dichromatic (,red,green colour-blind') and trichromatic marmosets were compared. Visual stimuli included coloured and achromatic gratings, and spatially uniform red and green lights presented at varying temporal phases and frequencies. The sensitivity of PC cells to red,green chromatic modulation was found to depend primarily on the spectral separation between the medium- and long-wavelength-sensitive cone pigments (20 or 7 nm) in the two trichromatic marmoset phenotypes studied. The temporal frequency dependence of chromatic sensitivity was consistent with centre,surround interactions. Some evidence for chromatic selectivity was seen in peripheral PC cells. The receptive field dimensions of parvocellular cells were similar in dichromatic and trichromatic animals, but the achromatic contrast sensitivity of cells was slightly higher (by about 30%) in dichromats than in trichromats. These data support the hypothesis that the primary role of the PC is to transmit high-acuity spatial signals, with red,green opponent signals appearing as an additional response dimension in trichromatic animals. [source] Neural mechanisms of chromatic and achromatic visionCOLOR RESEARCH & APPLICATION, Issue 6 2008Arne Valberg Abstract Building upon electrophysiological recordings from the lateral geniculate nucleus (LGN) of the macaque monkey, we describe a model for neural processing of color and brightness/lightness information that starts in the cone receptors and continues in the opponent cells of the retina, LGN, and visual cortex. The excitation of the three cone types to direct stimulation by light is modified in accordance with a hyperbolic response function before providing inputs to retinal ganglion cells. Using weighted differences of such cone outputs, we simulate the responses of common types of opponent ganglion and geniculate cells to light modulation along the chromatic and luminance dimensions. Extrapolating the results of the simulation, we suggest a way in which the brain might combine inputs from the geniculate to obtain correlates of chromatic and achromatic color vision and of brightness/lightness perception. In particular, we demonstrate for the first time how combinations of "L,M" and "M,L" parvocellular ON- and OFF-opponent-cells may lead to a quantitative account of brightness and blackness scaling. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 433,443, 2008 [source] | ||||||||||||||||||||||