Knowledge integration based on the relationship between structure and function of the neural substrate is one of the main targets of neuroinformatics and data-driven computational modeling. However, the multiplicity of data sources, the diversity of benchmarks, the mixing of observables of different natures, and the necessity of a long-term, systematic approach make such a task challenging. Here we present a first snapshot of a long-term integrative modeling program designed to address this issue in the domain of the visual system: a comprehensive spiking model of cat primary visual cortex. The presented model satisfies an extensive range of anatomical, statistical and functional constraints under a wide range of visual input statistics. In the presence of physiological levels of tonic stochastic bombardment by spontaneous thalamic activity, the modeled cortical reverberations self-generate a sparse asynchronous ongoing activity that quantitatively matches a range of experimentally measured statistics. When integrating feed-forward drive elicited by a high diversity of visual contexts, the simulated network produces a realistic, quantitatively accurate interplay between visually evoked excitatory and inhibitory conductances; contrast-invariant orientation-tuning width; center surround interactions; and stimulus-dependent changes in the precision of the neural code. This integrative model offers insights into how the studied properties interact, contributing to a better understanding of visual cortical dynamics. It provides a basis for future development towards a comprehensive model of low-level perception.

• MeSH
• Action Potentials physiology   MeSH
• Cats MeSH
• Models, Neurological * MeSH
• Neurons physiology   MeSH
• Computer Simulation MeSH
• Primary Visual Cortex * physiology   MeSH
• Computational Biology * MeSH
• Visual Cortex physiology   MeSH
• Animals MeSH
• Check Tag
• Cats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH

We have studied the visual system of subterranean mole-rats of the rodent family Bathyergidae, for which light and vision seem of little importance. The eye diameter varies between 3.5mm in Bathyergus suillus and 1.3mm in Heterocephalus glaber. The small superficial eyes have features typical of sighted animals (clear optics, well-developed pupil and well-organized retina) and appear suited for proper image formation. The retinae are rod-dominated but possess rather high cone proportions of about 10%. The total number of retinal ganglion cells and optic nerve fibres ranges between 6000 in Bathyergus suillus and 2100 in Heliophobius argenteocinereus. Visual acuity (estimated from counts of peak ganglion cell density and axial length of the eye) is low, ranging between 0.3 and 0.5 cycles/degree. The retina projects to all the visual structures described in surface-dwelling sighted rodents. The suprachiasmatic nucleus is large and receives bilateral retinal input. All other visual nuclei are reduced in size and receive almost exclusively contralateral retinal projections of varying magnitude. The primary visual cortex is small and, in comparison to other rodents, displaced laterally. In conclusion, the African mole-rats possess relatively well-developed functional visual subsystems involved in photoperiodicity, form and brightness discrimination. In contrast, visual subsystems involved in coordination of visuomotor reflexes are severely reduced. This pattern suggests the retention of basic visual capabilities. Residual vision may enable subterranean mammals to localize breaches in the burrows that let in light thus providing a cue to enable mole-rats to reseal such entry points and to prevent entry of predators.

• MeSH
• Superior Colliculi anatomy & histology   MeSH
• Thalamic Nuclei MeSH
• Geniculate Bodies MeSH
• Mole Rats MeSH
• Suprachiasmatic Nucleus MeSH
• Retina anatomy & histology   MeSH
• Visual Pathways anatomy & histology   MeSH
• Visual Cortex anatomy & histology   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH

• MeSH
• Evoked Potentials MeSH
• Conditioning, Classical MeSH
• Rabbits MeSH
• Photic Stimulation MeSH
• Visual Cortex physiology   MeSH
• Animals MeSH
• Check Tag
• Rabbits MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH

Visual cortical circuits show profound plasticity during early life and are later stabilized by molecular "brakes" limiting excessive rewiring beyond a critical period. The mechanisms coordinating the expression of these factors during the transition from development to adulthood remain unknown. We found that miR-29a expression in the visual cortex dramatically increases with age, but it is not experience-dependent. Precocious high levels of miR-29a blocked ocular dominance plasticity and caused an early appearance of perineuronal nets. Conversely, inhibition of miR-29a in adult mice using LNA antagomirs activated ocular dominance plasticity, reduced perineuronal nets, and restored their juvenile chemical composition. Activated adult plasticity had the typical functional and proteomic signature of critical period plasticity. Transcriptomic and proteomic studies indicated that miR-29a manipulation regulates the expression of plasticity brakes in specific cortical circuits. These data indicate that miR-29a is a regulator of the plasticity brakes promoting age-dependent stabilization of visual cortical connections.

• Keywords
• DNA methylation, microRNA, ocular dominance plasticity, perineuronal net,
• MeSH
• MicroRNAs * genetics   MeSH
• Mice, Inbred C57BL MeSH
• Mice MeSH
• Neuronal Plasticity genetics   MeSH
• Dominance, Ocular genetics   MeSH
• Proteomics MeSH
• Visual Cortex * MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• MicroRNAs * MeSH
• MIRN29 microRNA, mouse MeSH Browser

• MeSH
• Electroencephalography MeSH
• Electrophysiology MeSH
• Evoked Potentials MeSH
• Rabbits MeSH
• Geniculate Bodies physiology   MeSH
• Cerebral Cortex physiology   MeSH
• Neural Analyzers MeSH
• Neurons drug effects   MeSH
• Strychnine pharmacology   MeSH
• Light MeSH
• Vision, Ocular * MeSH
• Visual Cortex drug effects   physiology   MeSH
• Animals MeSH
• Check Tag
• Rabbits MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Strychnine MeSH

PURPOSE: The purpose of the article is to present the history and current status of visual cortical neuroprostheses, and to present a new method of stimulating intact visual cortex cells. METHODS: This paper contains an overview of the history and current status of visual cortex stimulation in severe visual impairment, but also highlights its shortcomings. These include mainly the stimulation of currently damaged cortical cells over a small area and, from a morphological point of view, possible damage to the stimulated neurons by the electrodes and their encapsulation by gliotic tissue. RESULTS: The paper also presents a proposal for a new technology of image processing and its transformation into a form of non-invasive transcranial stimulation of undamaged parts of the brain, which is protected by a national and international patent. CONCLUSION: The paper presents a comprehensive review of the current options for compensating for lost vision at the level of the cerebral cortex and a proposal for a new non-invasive method of stimulating the functional neurons of the visual cortex.

• Keywords
• visual neuroprosthesis, cortical visual centers, transcranial stimulation,
• MeSH
• Humans MeSH
• Brain * physiology   MeSH
• Neurons MeSH
• Vision Disorders MeSH
• Vision, Ocular MeSH
• Visual Cortex * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Systematic Review MeSH

Visual attention modulates the firing rate of neurons in many primate cortical areas. In V4, a cortical area in the ventral visual pathway, spatial attention has also been shown to reduce the tendency of neurons to fire closely separated spikes (burstiness). A recent model proposes that a single mechanism accounts for both the firing rate enhancement and the burstiness reduction in V4, but this has not been empirically tested. It is also unclear if the burstiness reduction by spatial attention is found in other visual areas and for other attentional types. We therefore recorded from single neurons in the medial superior temporal area (MST), a key motion-processing area along the dorsal visual pathway, of two rhesus monkeys while they performed a task engaging both spatial and feature-based attention. We show that in MST, spatial attention is associated with a clear reduction in burstiness that is independent of the concurrent enhancement of firing rate. In contrast, feature-based attention enhances firing rate but is not associated with a significant reduction in burstiness. These results establish burstiness reduction as a widespread effect of spatial attention. They also suggest that in contrast to the recently proposed model, the effects of spatial attention on burstiness and firing rate emerge from different mechanisms.

• Keywords
• attention, burstiness, monkey neurophysiology, visual cortex,
• MeSH
• Biological Clocks physiology   MeSH
• Macaca mulatta MeSH
• Brain Waves physiology   MeSH
• Nerve Net physiology   MeSH
• Attention physiology   MeSH
• Space Perception physiology   MeSH
• Visual Fields physiology   MeSH
• Visual Cortex physiology   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

In the present study, we aimed at determining the metabolic responses of the human visual cortex during the presentation of chromatic and achromatic stimuli, known to preferentially activate two separate clusters of neuronal populations (called "blobs" and "interblobs") with distinct sensitivity to color or luminance features. Since blobs and interblobs have different cytochrome-oxidase (COX) content and micro-vascularization level (i.e., different capacities for glucose oxidation), different functional metabolic responses during chromatic vs. achromatic stimuli may be expected. The stimuli were optimized to evoke a similar load of neuronal activation as measured by the bold oxygenation level dependent (BOLD) contrast. Metabolic responses were assessed using functional 1H MRS at 7 T in 12 subjects. During both chromatic and achromatic stimuli, we observed the typical increases in glutamate and lactate concentration, and decreases in aspartate and glucose concentration, that are indicative of increased glucose oxidation. However, within the detection sensitivity limits, we did not observe any difference between metabolic responses elicited by chromatic and achromatic stimuli. We conclude that the higher energy demands of activated blobs and interblobs are supported by similar increases in oxidative metabolism despite the different capacities of these neuronal populations.

• Keywords
• MR spectroscopy, energy metabolism, functional MRI, glutamate, lactate,
• MeSH
• Color * MeSH
• Energy Metabolism MeSH
• Glucose metabolism   MeSH
• Aspartic Acid metabolism   MeSH
• Glutamic Acid metabolism   MeSH
• Lactic Acid metabolism   MeSH
• Humans MeSH
• Magnetic Resonance Spectroscopy MeSH
• Magnetic Resonance Imaging MeSH
• Brain Chemistry physiology   MeSH
• Neurons physiology   MeSH
• Oxidation-Reduction MeSH
• Electron Transport Complex IV metabolism   MeSH
• Photic Stimulation * MeSH
• Healthy Volunteers MeSH
• Evoked Potentials, Visual MeSH
• Visual Cortex metabolism   physiology   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Glucose MeSH
• Aspartic Acid MeSH
• Glutamic Acid MeSH
• Lactic Acid MeSH
• Electron Transport Complex IV MeSH

To study the neural mechanisms of interhippocampal transfer of lateralized place navigation engrams in rats, lidocaine was injected via chronically implanted cannulae to reversibly inactivate the hippocampal formation and the visual cortex on one side. The eye opposite the blocked side was occluded. Under these conditions, rats learned the location of an invisible platform in a water maze [mean escape latencies per four-trial block (t) = 5-6 s at the performance asymptote]. Monocular intact brain retrieval with the trained eye (t = 7) was better than with the untrained eye (t = 13). However, analysis of each retrieval trial indicated untrained eye performance was only poor on the first trial (t = 30). To test whether trans-commissural read-out alone or write-in (i.e. interhippocampal transfer) of the lateralized engram explains the above results, rats acquired a new platform location (t = 5). Two groups were then given a 30-s "free swim" (the platform was removed) with intact brain and either the trained or untrained eye occluded. A third group did not have this "transfer" trial. Retrieval was tested with the trained hippocampus and visual cortex blocked. With the trained eye occluded, retrieval in the rats that had the transfer trial (t = 11) was better than in those that did not (t = 25), but slightly worse than in rats tested with the untrained eye, hippocampus and visual cortex blocked (t = 7). Additionally, retrieval was similar, independent of whether the trained (t = 12) or untrained (t = 11) eye was open on the transfer swim. The 30-s swim alone did not induce comparable savings. We conclude that interhippocampal transfer of lateralized place learning is easily induced, is equal if the transfer is facultative or imperative, and involves both trans-commissural read-out and write-in processes.

• MeSH
• Hippocampus anatomy & histology   drug effects   physiology   MeSH
• Rats MeSH
• Lidocaine pharmacology   MeSH
• Conditioning, Operant drug effects   MeSH
• Orientation drug effects   MeSH
• Memory physiology   MeSH
• Vision, Monocular physiology   MeSH
• Space Perception physiology   MeSH
• Visual Cortex anatomy & histology   drug effects   physiology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Lidocaine MeSH

Several laboratories have consistently reported small concentration changes in lactate, glutamate, aspartate, and glucose in the human cortex during prolonged stimuli. However, whether such changes correlate with blood oxygenation level-dependent functional magnetic resonance imaging (BOLD-fMRI) signals have not been determined. The present study aimed at characterizing the relationship between metabolite concentrations and BOLD-fMRI signals during a block-designed paradigm of visual stimulation. Functional magnetic resonance spectroscopy (fMRS) and fMRI data were acquired from 12 volunteers. A short echo-time semi-LASER localization sequence optimized for 7 Tesla was used to achieve full signal-intensity MRS data. The group analysis confirmed that during stimulation lactate and glutamate increased by 0.26 ± 0.06 μmol/g (~30%) and 0.28 ± 0.03 μmol/g (~3%), respectively, while aspartate and glucose decreased by 0.20 ± 0.04 μmol/g (~5%) and 0.19 ± 0.03 μmol/g (~16%), respectively. The single-subject analysis revealed that BOLD-fMRI signals were positively correlated with glutamate and lactate concentration changes. The results show a linear relationship between metabolic and BOLD responses in the presence of strong excitatory sensory inputs, and support the notion that increased functional energy demands are sustained by oxidative metabolism. In addition, BOLD signals were inversely correlated with baseline γ-aminobutyric acid concentration. Finally, we discussed the critical importance of taking into account linewidth effects on metabolite quantification in fMRS paradigms.

• MeSH
• Adult MeSH
• gamma-Aminobutyric Acid metabolism   MeSH
• Glucose metabolism   MeSH
• Glutamic Acid metabolism   MeSH
• Lactic Acid metabolism   MeSH
• Oxygen blood   MeSH
• Middle Aged MeSH
• Humans MeSH
• Magnetic Resonance Imaging MeSH
• Young Adult MeSH
• Photic Stimulation * MeSH
• Visual Cortex physiology   MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• gamma-Aminobutyric Acid MeSH
• Glucose MeSH
• Glutamic Acid MeSH
• Lactic Acid MeSH
• Oxygen MeSH