Spontaneous eyeblink rate predicts the strength of visuomotor binding

The primate cortex represents the external world in a distributed way, which requires for a mechanism that integrates the features of a processed event. Animal and patients studies suggest that feature binding in the visual cortex is under muscarinic-cholinergic control, whereas visuomotor integration is driven by the dopaminergic system. Consistent with this picture, we present evidence that the binding of visual and action features is modulated by spontaneous eyeblink rate (EBR), which is a functional marker of central dopaminergic function. Remarkably, the impact of EBR was restricted to the task-relevant visuomotor binding, suggesting that dopamine increased the maintenance of task-relevant information.     

Stress modulation of visuomotor binding

The primate cortex represents perceived and produced events in a distributed way, which calls for a mechanism that integrates their features into coherent structures. Animal, drug, and patient studies suggest that the local binding of visual features is under muscarinic–cholinergic control, whereas visuomotor binding seems to be driven by dopaminergic pathways. Consistent with this picture, we present evidence that the binding of visual features and actions is modulated by stress, induced by the cold pressure test (CPT), which causes an excessive dopamine turnover in prefrontal cortex. The impact of stress was restricted to the task-relevant visuomotor binding, supporting claims that dopamine affects the maintenance of task-relevant information in working memory. The outcome pattern, including the impact of the personality trait extraversion, suggests that the relation between dopamine level and visuomotor performance follows an inverted U-shaped function, with strongest binding being associated with average dopamine levels.     

Caffeine, but not nicotine, enhances visual feature binding

The distributed organization of the human visual cortex calls for a mechanism that integrates and binds the features of a perceived event, and neural synchronization is a prime candidate to serve that purpose. Animal studies suggest that synchronization in the visual cortex is enhanced by the muscarinic cholinergic system. Here we show that in healthy humans the binding of shape and colour, and of shape and location, of visual objects is increased by stimulating the muscarinic cholinergic system (caffeine consumption) but not by stimulating the nicotinic cholinergic system (nicotine consumption). Binding across perception and action is unaffected by either manipulation, suggesting a specific link between the visual system and the muscarinic cholinergic system.     

Plasticity of 5-hydroxytryptamine(1B) receptors during postnatal development in the rat visual cortex.

The distribution of 5-hydroxytryptamine1A and 5-hydroxytryptamine1B receptors in the visual cortex was studied by quantitative autoradiography during postnatal development. Overall, receptor densities increased throughout development, but exhibited regional rearrangements, particularly in the case of 5-hydroxytryptamine1B receptors. Neonatal treatment with 5,7-dihydroxytryptamine, which causes selective degeneration of serotoninergic neurons, had no effect on the density of 5-hydroxytryptamine1A receptors in the visual cortex. However, a transient increase in 5-hydroxytryptamine1B at postnatal days 10-12 was observed after this treatment, suggesting a regulation of postsynaptic receptors. Neonatal enucleation resulted in a marked increase in 5-hydroxytryptamine1B binding sites in all layers of the visual cortex by P16, whereas it had no effect upon 5-hydroxytryptamine1A binding sites. These results show that both receptor subtypes do not exhibit striking transient features in the visual cortex during postnatal development, but rather undergo discrete reorganizations. 5-Hydroxytryptamine1B receptors show changes in density after either neonatal degeneration of serotoninergic neurons or enucleation, indicating that the serotoninergic system involving this receptor subtype can exhibit some postnatal plasticity in the visual cortex.     

Brain functional network connectivity based on a visual task: visual information processing-related brain regions are significantly activated in the task state

It is not clear whether the method used in functional brain-network related research can be applied to explore the feature binding mechanism of visual perception. In this study, we investigated feature binding of color and shape in visual perception. Functional magnetic resonance imaging data were collected from 38 healthy volunteers at rest and while performing a visual perception task to construct brain networks active during resting and task states. Results showed that brain regions involved in visual information processing were obviously activated during the task. The components were partitioned using a greedy algorithm, indicating the visual network existed during the resting state. Z-values in the vision-related brain regions were calculated, confirming the dynamic balance of the brain network. Connectivity between brain regions was determined, and the result showed that occipital and lingual gyri were stable brain regions in the visual system network, the parietal lobe played a very important role in the binding process of color features and shape features, and the fusiform and inferior temporal gyri were crucial for processing color and shape information. Experimental findings indicate that understanding visual feature binding and cognitive processes will help establish computational models of vision, improve image recognition technology, and provide a new theoretical mechanism for feature binding in visual perception.     

Dopaminergic innervation of the primary visual cortex in the rat, and some correlations with human cortex

Dopaminergic terminals have been identified in the primary visual cortex with three techniques; immunocytochemistry with an anti-dopamine antiserum, retrograde axonal transport techniques using unconjugated wheat germ agglutinin and HPLC determination of catecholamines and metabolites in microdissected sub-regions of occipital cortex in the rat. The results demonstrate a specific dopaminergic innervation, arising from the ventral tegmental area, which is found mainly in laminae VI and V, but with minor innervation also in lamina I. Dopaminergic innervation to adjacent cortical regions is also described. Neurochemical data from post-mortem human material suggests that a similar innervation exists in man. An analysis of the distribution of dopaminergic fibres in relation to the known connections and possible functions of the deep laminae of visual cortex suggests that dopaminergic axons may participate in the corticofugal control of visual afferent pathways.     

From qualia to quantia: a system to document and quantify phosphene percepts elicited by non-invasive neurostimulation of the human occipital cortex

The stimulation of the occipital cortex induces transient visual percepts, known as phosphenes. The characterization and analysis of the features of these visual qualia can provide a window into the physiology and neuroanatomy of cerebral visual networks of humans. Phosphenes can be reliably elicited in humans by a variety of invasive and non-invasive techniques that depolarize visual cortex neurons. Nonetheless both research into their neural basis and categorization of their features are ultimately reliant on subjective self-reports. A variety of methods have been employed to provide a more objective means of recording the localization and morphology of neurostimulation-induced phosphenes. In spite of these attempts, phosphenes remain difficult to measure. A standard technique able to both document the myriad of features characterizing phosphenes in a flexible manner and allow a systematic quantitative comparison across groups or repeated measures is lacking. We hereby provide detailed instructions on how to use off-the-shelf components to construct and implement the LTaP (laser tracking and painting system) system for a relatively objective and real-time documentation of the presence, shape, area, spatial location and distribution of phosphenes in visual space. We further provide experimental data demonstrating the feasibility and reliability of the LTaP system to accurately capture established features of phosphenes induced by transcranial magnetic stimulation (TMS) of occipital cortex.     

Selective and divided attention during visual discriminations of shape, color, and speed: functional anatomy by positron emission tomography

Positron emission tomography (PET) was used to identify the neural systems involved in discriminating the shape, color, and speed of a visual stimulus under conditions of selective and divided attention. Psychophysical evidence indicated that the sensitivity for discriminating subtle stimulus changes in a same-different matching task was higher when subjects selectively attended to one attribute than when they divided attention among the attributes. PET measurements of brain activity indicated that modulations of extrastriate visual activity were primarily produced by task conditions of selective attention. Attention to speed activated a region in the left inferior parietal lobule. Attention to color activated a region in the collateral sulcus and dorsolateral occipital cortex, while attention to shape activated collateral sulcus (similarly to color), fusiform and parahippocampal gyri, and temporal cortex along the superior temporal sulcus. Outside the visual system, selective and divided attention activated nonoverlapping sets of brain regions. Selective conditions activated globus pallidus, caudate nucleus, lateral orbitofrontal cortex, posterior thalamus/colliculus, and insular-premotor regions, while the divided condition activated the anterior cingulate and dorsolateral prefrontal cortex. The results in the visual system demonstrate that selective attention to different features modulates activity in distinct regions of extrastriate cortex that appear to be specialized for processing the selected feature. The disjoint pattern of activations in extravisual brain regions during selective- and divided-attention conditions also suggests that preceptual judgements involve different neural systems, depending on attentional strategies.     

Cannabis, cocaine, and visuomotor integration: evidence for a role of dopamine D1 receptors in binding perception and action

The primate cortex represents and produces events in a distributed way, which calls for a mechanism that integrates their features into coherent structures. Visuomotor integration seems to be driven by dopaminergic (DA) pathways but which subsystems are involved is currently unknown. The present study compared the impact of the recreational use of two drugs on visuomotor integration: cannabis, which primarily targets dopaminergic D1 receptors, and cocaine, which mainly targets D2 receptors. Our findings show that cannabis but not cocaine use affects the strength of the binding between task-relevant stimulus features and the accompanying response. In contrast, cocaine but not cannabis use eliminates the inhibition of return. The observed pattern suggests that visuomotor integration is driven by DA/D1, but not DA/D2 receptor systems.     

Prefrontal cortex hemispheric specialization for categorical and coordinate visual spatial memory

During visual spatial perception of multiple items, the left hemisphere has been shown to preferentially process categorical spatial relationships while the right hemisphere has been shown to preferentially process coordinate spatial relationships. We hypothesized that this hemispheric processing distinction would be reflected in the prefrontal cortex during categorical and coordinate visual spatial memory, and tested this hypothesis using functional magnetic resonance imaging (fMRI). During encoding, abstract shapes were presented in the left or right hemifield in addition to a dot at a variable distance from the shape (with some dots on the shape); participants were instructed to remember the position of each dot relative to the shape. During categorical memory retrieval, each shape was presented centrally and participants responded whether the previously corresponding dot was 'on' or 'off' of the shape. During coordinate memory retrieval, each shape was presented centrally and participants responded whether the previously corresponding dot was 'near' or 'far' from the shape (relative to a reference distance). Consistent with our hypothesis, a region in the left prefrontal cortex (BA10) was preferentially associated with categorical visual spatial memory and a region in the right prefrontal cortex (BA9/10) was preferentially associated with coordinate visual spatial memory. These results have direct implications for interpreting previous findings that the left prefrontal cortex is associated with source memory, as this cognitive process is categorical in nature, and the right prefrontal cortex is associated with item memory, as this process depends on the precise spatial relations among item features or components.     

Relatively spared mesocorticolimbic dopaminergic system in juvenile parkinsonism

This study aims to examine the function of the mesocorticolimbic dopaminergic system, including the amygdala, in recognizing emotions in juvenile parkinsonism (JP). Eleven patients with JP and 16 age-matched controls selected one basic emotion (happiness, sadness, anger, fear, surprise, or disgust) that best described the emotional state represented by visual and auditory stimuli. There was no significant difference between the patients and normal controls in their recognition of emotions. The spared emotion recognition in JP could be attributed to the absence of any pathological changes or the normal dopamine concentrations in the mesocorticolimbic system in this condition.     

Plasticity of 5-hydroxytryptamine1B receptors during postnatal development in the rat visual cortex

The distribution of 5-hydroxytryptamine_1A and 5-hydroxytryptamine_1B receptors in the visual cortex was studied by quantitative autoradiography during postnatal development. Overall, receptor densities increased throughout development, but exhibited regional rearrangements, particularly in the case of 5-hydroxytryptamine_1B receptors. Neonatal treatment with 5,7-dihydroxytryptamine, which causes selective degeneration of serotoninergic neurons, had no effect on the density of 5-hydroxytryptamine_1A receptors in the visual cortex. However, a transient increase in 5-hydroxytryptamine_1B at postnatal days 10–12 was observed after this treatment, suggesting a regulation of postsynaptic receptors. Neonatal enucleation resulted in a marked increase in 5-hydroxytryptamine_1B binding sites in all layers of the visual cortex by P16, whereas it had no effect upon 5-hydroxytryptamine_1A binding sites.These results show that both receptor subtypes do not exhibit striking transient features in the visual cortex during postnatal development, but rather undergo discrete reorganizations. 5-Hydroxytryptamine_1B receptors show changes in density after either neonatal degeneration of serotoninergic neurons or enucleation, indicating that the serotoninergic system involving this receptor subtype can exhibit some postnatal plasticity in the visual cortex.     

Associations among central nervous, endocrine, and immune activities when positive emotions are elicited by looking at a favorite person

Recent studies on psychoneuroimmunology have indicated that positive psychological events are related to immune functions; however, limited information is available regarding associations among the central nervous, endocrine, and immune systems when positive emotions are elicited. In the present study, we demonstrated associations among these systems by simultaneously recording brain, endocrine, and immune activities when positive emotions were evoked in participants as they watched films featuring their favorite persons. Interestingly, the activity of peripheral circulating natural killer cells and the peripheral dopamine level were elevated while participants experienced positive emotions, and these values were positively correlated. The following brain regions were significantly activated in the positive condition relative to the control condition: medial prefrontal cortex, thalamus, hypothalamus, subcallosal gyrus, posterior cingulate cortex, superior temporal gyrus, and cerebellum. Further, covariate analyses indicated that these brain regions were temporally associated with endocrine and immune activities. These results suggest that while an individual experiences positive emotions, the central nervous, endocrine, and immune systems may be interrelated and attraction for favorite persons may be associated with the activation of the innate immune function via the dopaminergic system.     

When moving faces activate the house area: an fMRI study of object-file retrieval

Background  

The visual cortex of the human brain contains specialized modules for processing different visual features of an object. Confronted with multiple objects, the system needs to attribute the correct features to each object (often referred to as 'the binding problem'). The brain is assumed to integrate the features of perceived objects into object files – pointers to the neural representations of these features, which outlive the event they represent in order to maintain stable percepts of objects over time. It has been hypothesized that a new encounter with one of the previously bound features will reactivate the other features in the associated object file according to a kind of pattern-completion process.     

Binding in visual working memory: the role of the episodic buffer

The episodic buffer component of working memory is assumed to play a central role in the binding of features into objects, a process that was initially assumed to depend upon executive resources. Here, we review a program of work in which we specifically tested this assumption by studying the effects of a range of attentionally demanding concurrent tasks on the capacity to encode and retain both individual features and bound objects. We found no differential effect of concurrent load, even when the process of binding was made more demanding by separating the shape and color features spatially, temporally or across visual and auditory modalities. Bound features were however more readily disrupted by subsequent stimuli, a process we studied using a suffix paradigm. This suggested a need to assume a feature-based attentional filter followed by an object based storage process. Our results are interpreted within a modified version of the multicomponent working memory model. We also discuss work examining the role of the hippocampus in visual feature binding.     

Ontogeny of dopaminergic function in the rat midbrain tegmentum, corpus striatum and frontal cortex

Ontogenic development of the dopaminergic system in rat brain was investigated. This was accomplished by monitoring changes in postsynaptic dopamine receptor formation and presynaptic dopamine content in the midbrain tegmentum, frontal cortex and corpus striatum from the 18th day of gestation through adulthood. The dopamine antagonist spiperone was used as the binding ligand to quantitate receptor number while dopamine content was measured chromatographically. [3H]Spiperone binding kinetics in adult animals revealed that the maximum number of receptor sites (Bmax) was 160, 900 and 597 fmol/mg protein in midbrain tegmentum, frontal cortex and corpus striatum, respectively, while the corresponding equilibrium constant (Kd) values were 0.15, 0.52 and 0.15 nM. During the course of development, the affinity for spiperone binding in corpus striatum and frontal cortex did not change significantly, while in midbrain tegmentum the binding affinity in younger animals was significantly lower. Results from competitive inhibition experiments using various serotonergic and dopaminergic antagonists suggested that at all ages dopamine D2-receptors were responsible for spiperone binding in corpus striatum and midbrain tegmentum. In frontal cortex, binding properties consistent with D2-receptors were observed in non-adult animals; by the time adulthood was reached, however, spiperone binding characteristics were altered and appeared to correspond to serotonin sites. The developmental patterns of the dopaminergic markers were different in all 3 tissues. Adult receptor levels were achieved very early in midbrain tegmentum, while increases in receptor number continued in corpus striatum and frontal cortex, at different rates, throughout the postnatal period. A marked increase in dopamine in corpus striatum occurred during the second and third postnatal weeks and the transmitter content remained relatively constant after this time. Transient fluctuations in endogenous dopamine during the postnatal period were observed in midbrain tegmentum and frontal cortex. A general feature of the ontogenic pattern in all tissues appeared to be increases in dopamine receptor preceding increases in dopamine synthesis. A hypothesis on the developmental regulation of dopamine neurons was derived.     

Texture-surround suppression of contour-shape coding in human vision

Contextual influences on neurons in the primary visual cortex have largely been studied using simple visual stimuli and their functional role is still poorly understood. Using a novel visual after-effect of perceived shape we show psychophysically that the coding of a contour's shape is inhibited by nearby parallel, but not orthogonal texture orientations. This suggests that neurons in the visual cortex that are suppressed by parallel orientations feed their outputs into higher visual areas that are involved in the processing of contour shape and in the recognition of objects.     

Dark-rearing affects the development of benzodiazepine receptors in the central visual structures of rat brain

The postnatal development of [3H]flunitrazepam binding to benzodiazepine receptors has been studied in the retina, lateral geniculate nucleus, superior colliculus, frontal cortex and visual cortex of the rat. In the frontal and visual cortices, binding reached the highest level at postnatal day 25 and then decreased slightly until adulthood. In the superior colliculus, the adult value of [3H]flunitrazepam binding is already reached at postnatal day 25, whereas in the retina the highest binding was found at postnatal day 50. The ontogeny of benzodiazepine binding sites in the visual regions does not essentially differ from that in other brain regions, suggesting that the appearance of [3H]flunitrazepam binding sites in the visual system is not correlated with the development of retinal function and the functional maturation of the visual system with regard to processing of light stimuli. Raising rats in complete darkness from birth until the age of 25 days resulted in significantly decreased binding levels in the lateral geniculate nucleus and in the superior colliculus by 29% and 17%, respectively, as compared to controls. [3H]Flunitrazepam binding in the other regions studied was not affected by dark-rearing. Presumably, the complete lack of visual experience interferes with the functional development of GABAergic mechanisms involved in the gating function of the subcortical visual centres for visual information transfer.     

Neurochemical observations in a case of Pick's disease

Neurochemical markers of the activities of the cholinergic, gabaergic and dopaminergic systems were measured in post-mortem brain from a case of Pick's disease. No marked changes were found in the activities of choline acetyltransferase, acetylcholinesterase, l-glutamic acid decarboxylase and the concentration of dopamine. In areas of brain showing no histological changes, muscarinic receptor binding was within the normal range. In the cerebral cortex, which exhibited the neuropathological features of Pick's disease, the number of muscarinic cholinergic binding sites was much reduced, suggesting that the cortical neurones which are lost in Pick's disease are cholinoceptive.