Home About us Contact
|
Home About us Contact | ||
|
|
||
Visual Responses (visual + response)
Selected AbstractsVisual 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] 9- cis Retinal Increased in Retina of RPE65 Knockout Mice with Decrease in Coat Pigmentation,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2006Jie Fan The protein RPE65 is essential for the generation of the native chromophore, 11- cis retinal, of visual pigments. However, the Rpe65 knockout (Rpe65 -1- ) mouse shows a minimal visual response due to the presence of a pigment, isorhodopsin, formed with 9- cis retinal. Isorhodopsin accumulates linearly with prolonged dark-rearing of the animals. The majority of Rpe65 -/- mice have an agouti coat color. A tan coat color subset of Rpe65 -/- mice was found to have an enhanced visual response as measured by electroretinograms. The enhanced response was found to be due to increased levels of 9- cis retinal and isorhodopsin pigment levels. Animals of both coat colors reared in cyclic light have minimal levels of regenerated pigment and show photoreceptor degeneration. On dark-rearing, pigment accumulates and photoreceptor degeneration is decreased. In the tan Rpe65 -/- mice, the level of photoreceptor degeneration is less than in the agouti animals, which have an increased pigment and decreased free opsin level. Therefore, photoreceptor damage correlates with the amount of the apoprotein present, supporting findings that the activity from unregenerated opsin can lead to photoreceptor degeneration. [source] Attention-like processes underlying optomotor performance in a Drosophila choice mazeDEVELOPMENTAL NEUROBIOLOGY, Issue 2 2007Bruno van Swinderen Abstract The authors present a novel paradigm for studying visual responses in Drosophila. An eight-level choice maze was found to reliably segregate fly populations according to their responses to moving stripes displayed on a computer screen. Visual responsiveness was robust in wild-type flies, and performance depended on salience effects such as stimulus color and speed. Analysis of individual fly choices in the maze revealed that stereotypy, or choice persistence, contributed significantly to a strain's performance. On the basis of these observations, the authors bred wild-type flies for divergent visual phenotypes by selecting individual flies displaying extreme stereotypy. Selected flies alternated less often in the sequential choice maze than unselected flies, showing that stereotypy could evolve across generations. The authors found that selection for increased stereotypy impaired flies' responsiveness to competing stimuli in tests for attention-like behavior in the maze. Visual selective attention was further investigated by electrophysiology, and it was found that increased stereotypy also impaired responsiveness to competing stimuli at the level of brain activity. Combined results present a comprehensive approach to studying visual responses in Drosophila, and show that behavioral performance involves attention-like processes that are variable among individuals and thus sensitive to artificial selection. © 2006 Wiley Periodicals, Inc. Develop Neurobiol 67: 129,145, 2007. [source] The "smellscape" of mother's breast: Effects of odor masking and selective unmasking on neonatal arousal, oral, and visual responsesDEVELOPMENTAL PSYCHOBIOLOGY, Issue 2 2007Sébastien Doucet Abstract Lactating women emit odor cues that release activity in newborns. Such cues may be carried in various substrates, including milk or areolar secretions. The present study aimed to examine the responses of infants facing their mother's breast and to sort out the source(s) of active volatile compounds emitted by the lactating breast. Infants (aged 3,4 days) were presented their mother's breast in two consecutive trials of 90 s each: a scentless condition (breast entirely covered with a transparent film) paired with one of four odorous conditions (fully exposed breast: n,=,15; nipple only exposed: 15; areola only exposed: 13; and milk exposed: 12). The infants were more orally activated when facing any of the odorous breast conditions than when facing the scentless breast. They cried earlier and longer, and opened their eyes less, when facing the scentless breast. Nipple, Areola, and Milk odors appeared to be equivalent to the whole breast odor in stimulating oral activity and in delaying crying onset. This study shows that volatile compounds originating in areolar secretions or milk release mouthing, stimulate eye opening, and delay and reduce crying in newborns. © 2007 Wiley Periodicals, Inc. Dev Psychobiol 49: 129,138, 2007. [source] Callosal contribution to ocular dominance in rat primary visual cortexEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2010Chiara Cerri Abstract Ocular dominance (OD) plasticity triggered by monocular eyelid suture is a classic paradigm for studying experience-dependent changes in neural connectivity. Recently, rodents have become the most popular model for studies of OD plasticity. It is therefore important to determine how OD is determined in the rodent primary visual cortex. In particular, cortical cells receive considerable inputs from the contralateral hemisphere via callosal axons, but the role of these connections in controlling eye preference remains controversial. Here we have examined the role of callosal connections in binocularity of the visual cortex in naïve young rats. We recorded cortical responses evoked by stimulation of each eye before and after acute silencing, via stereotaxic tetrodotoxin (TTX) injection, of the lateral geniculate nucleus ipsilateral to the recording site. This protocol allowed us to isolate visual responses transmitted via the corpus callosum. Cortical binocularity was assessed by visual evoked potential (VEP) and single-unit recordings. We found that acute silencing of afferent geniculocortical input produced a very significant reduction in the contralateral-to-ipsilateral (C/I) VEP ratio, and a marked shift towards the ipsilateral eye in the OD distribution of cortical cells. Analysis of absolute strength of each eye indicated a dramatic decrease in contralateral eye responses following TTX, while those of the ipsilateral eye were reduced but maintained a more evident input. We conclude that callosal connections contribute to normal OD mainly by carrying visual input from the ipsilateral eye. These data have important implications for the interpretation of OD plasticity following alterations of visual experience. [source] Noise-improved signal detection in cat primary visual cortex via a well-balanced stochastic resonance-like procedureEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2007Klaus Funke Abstract Adding noise to a weak signal can paradoxically improve signal detection, a process called ,stochastic resonance' (SR). In the visual system, noise might be introduced by the image jitter resulting from high-frequency eye movements, like eye microtremor and microsaccades. To test whether this kind of noise might be beneficial or detrimental for cortical signal detection, we performed single-unit recordings from area 17 of anaesthetized cats while jittering the visual stimulus in a frequency and amplitude range resembling the possible range of eye movements. We used weak, sub- and peri-threshold visual stimuli, on top of which we superimposed noise with variable jitter amplitude. In accordance with the typical SR effect, we found that small noise levels actually increased the signal-to-noise ratio (SNR) of previously weak cortical visual responses, while originally strong responses were little affected or even reduced. Above a certain noise level, the SNR dropped a little, but not as a result of increased background activity , as would be proposed by SR theory , but because of a lowered response to signal and noise. Therefore, it seems that the ascending visual pathway optimally utilizes signal detection improvement by a SR-like process, while at the same time preventing spurious noise-induced activity and keeping the SNR sufficiently high. [source] Postnatal maturation of GABAA and GABAC receptor function in the mammalian superior colliculusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2001Mathias Boller Abstract In the stratum griseum superficiale (SGS) of the mammalian superior colliculus, GABAC receptors seem to control the excitability of projection neurons by selective inactivation of local GABAergic interneurons. As the onset of visual responses to SC begins well after birth in the rat, it is possible to study developmental changes in GABAergic mechanisms that are linked to the onset of visual information processing. In order to analyse postnatal changes in inhibitory mechanisms that involve GABA receptor function, we used extracellular field potential (FP) recordings and single cell patch-clamp techniques in slices from postnatal day 4 (P4) to P32 and examined the effects of GABA and muscimol on electrically evoked SGS cell activity. While GABAA receptor activation affected FP amplitudes throughout postnatal development, GABAC receptor activation did not significantly change FP amplitudes until the third postnatal week. Results from patch-clamping single cells, however, clearly demonstrate that GABAC receptors are already functional at P4 , similar to GABAA receptors. Throughout postnatal development, activation of GABAC receptors leads to a strong inhibition of inhibitory postsynaptic activity, indicating that GABAC receptors are expressed by inhibitory interneurons. Furthermore, the proportion of neurons that show decreased excitatory postsynaptic activity during GABAC receptor activation correlates with the proportion of GABAergic interneurons in SGS. Our patch-clamp results indicate that the functional expression of GABAC receptors by GABAergic interneurons does not change significantly during postnatal development. However, our measurements of FP amplitudes indicate that the maturation of the efferent connections of these GABAergic neurons within SGS during the third postnatal week strongly changes GABAC receptor function. [source] Attentional load modifies early activity in human primary visual cortexHUMAN BRAIN MAPPING, Issue 5 2009Karsten S. Rauss Abstract Recent theories of selective attention assume that the more attention is required by a task, the earlier are irrelevant stimuli filtered during perceptual processing. Previous functional MRI studies have demonstrated that primary visual cortex (V1) activation by peripheral distractors is reduced by higher task difficulty at fixation, but it remains unknown whether such changes affect initial processing in V1 or subsequent feedback. Here we manipulated attentional load at fixation while recording peripheral visual responses with high-density EEG in 28 healthy volunteers, which allowed us to track the exact time course of attention-related effects on V1. Our results show a modulation of the earliest component of the visual evoked potential (C1) as a function of attentional load. Additional topographic and source localization analyses corroborated this finding, with significant load-related differences observed throughout the first 100 ms post-stimulus. However, this effect was observed only when stimuli were presented in the upper visual field (VF), but not for symmetrical positions in the lower VF. Our findings demonstrate early filtering of irrelevant information under increased attentional demands, thus supporting models that assume a flexible mechanism of attentional selection, but reveal important functional asymmetries across the VF. Hum Brain Mapp 2009. © 2008 Wiley-Liss, Inc. [source] Testing visual function in the clinical settingCLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 4 2010Gerald Westheimer ASTC BSc PhD ScD Dr Med (hc) FAAO FRS The explosive growth of automatic examination of the eye, in particular for determining refractive corrections, invites an analysis of the strengths and limitations of these devices and their role in clinical decisions. Subjective refraction procedures are based on a patient's visual responses and these embrace many levels of additional optical and neural processing and factors involving the higher-order nervous system and perception. Because the ultimate mission is the maintenance and improvement of a patient's visual experiences, the optometric examination necessarily extends beyond the employment of automatic devices and therefore, should include engaging the patients in tests of their visual functions. [source] | ||||||||||