Feedback inhibition derived from the posterior parietal cortex regulates the neural properties of the mouse visual cortex

Feedback regulation from the higher association areas is thought to control the primary sensory cortex, contribute to the cortical processing of sensory information, and work for higher cognitive functions such as multimodal integration and attentional control. However, little is known about the underlying neural mechanisms. Here, we show that the posterior parietal cortex (PPC) persistently inhibits the activity of the primary visual cortex (V1) in mice. Activation of the PPC causes the suppression of visual responses in V1 and induces the short‐term depression, which is specific to visual stimuli. In contrast, pharmacological inactivation of the PPC or disconnection of cortical pathways from the PPC to V1 results in an effect of transient enhancement of visual responses in V1. Two‐photon calcium imaging demonstrated that the cortical disconnection caused V1 excitatory neurons an enhancement of visual responses and a reduction of orientation selectivity index (OSI). These results show that the PPC regulates the response properties of V1 excitatory neurons. Our findings reveal one of the functions of the PPC, which may contribute to higher brain functions in mice.     

Neurons in the visual cortex of Microtus brandti]

Neurons were described in the visual Cortex of Microtus brandti, a Mongolian harmful rodent living in day-activity. We find following types of neurons in our Golgi-material: 1. spiny neurons: pyramidal and stellate neurons. 2. smooth or sparsely spined neurons: smooth, large neurons, sparsely spined small neurons with descending axons, sparsely spined neurons with ascending axons. Double-bouquet-, chandelier and neuroglioforme cells are not impregnated. There are no bipolare neurons (Martinotti cells) among the neurons with ascending axons. The small, sparsely spined neurons are not only in lamina IV - like in other species - but they can also be found in laminae II to IV. Their distribution of spines on the distal parts of dendrites seems to be characteristical for rodents. The lamination of the visual cortex of Microtus brandti is the same like in the rat. All cells are of large size in relation to the body mass of the animal.     

Responses of squirrel visual cortex neurons to patterned visual stimuli]

The responses of visual cortical neurons to patterned visual stimuli were studied in squirrel Sciurus vulgaris. The direction selective, orientation-selective and non-selective neurons were observed. Most direction-selective and non-selective neurons were sensitive to high speeds of stimulus movement--hundreds deg/s. The direction-selective neurons exhibited their selectivity at such high speeds in spite of the short time of the stimulus movement through the receptive field. Orientation-selective neurons (with simple or complex receptive fields) were sensitive to lower speeds of the stimulus movement (tens deg/s). Some mechanisms of the properties described are discussed.     

Unidirectional visual motion adaptation induces reciprocal inhibition of human early visual cortex excitability

ObjectivesBehavioural observations provided by the waterfall illusion suggest that motion perception is mediated by a comparison of responsiveness of directional selective neurones. These are proposed to be optimally tuned for motion detection in different directions. Critically however, despite the behavioural observations, direct evidence of this relationship at a cortical level in humans is lacking. By utilising the state dependant properties of transcranial magnetic stimulation (TMS), one can probe the excitability of specific neuronal populations using the perceptual phenomenon of phosphenes.MethodWe exposed subjects to unidirectional visual motion adaptation and subsequently simultaneously measured early visual cortex (V1) excitability whilst viewing motion in the adapted and non-adapted direction.ResultFollowing adaptation, the probability of perceiving a phosphene whilst viewing motion in the adapted direction was diminished reflecting a reduction in V1 excitability. Conversely, V1 excitability was enhanced whilst viewing motion in the opposite direction to that used for adaptation.ConclusionOur results provide support that in humans a process of reciprocal inhibition between oppositely tuned directionally selective neurones in V1 facilitates motion perception.SignificanceThis paradigm affords a unique opportunity to investigate changes in cortical excitability following peripheral vestibular disorders.     

Nitric oxide synthase inhibition prevents neuronal death in the developing visual cortex

During postnatal development of the visual cortex of golden hamster, there is a transient increase in both the expression and the activity of nitric oxide synthase (NOS), which coincides temporally with the formation of ipsilateral retino-collicular and retino-geniculate projections and the functional differentiation of primary visual cortex, suggesting the involvement of NO in the maturation of the visual cortex. In the present study, an inhibitor of NOS, N-nitro-L-arginine (L-NNA) was used to block the NOS activity of newborn golden hamster, and effects on development were examined. L-NNA treatment caused an increase in mortality, and suppression of both body weight gain and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity in the early phase of treatment (before postnatal day 14, PD14). The growth of NADPH-d-positive neurons in the visual cortex was also suppressed by the treatment. In control animals, significant numbers of apoptotic neurons were detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling assay on PD14, and this apoptosis mainly affected cells in cortical layers II and III. NOS inhibition largely rescued neurons from undergoing apoptosis, indicating that NO may serve as a signal triggering apoptosis and play a role in the maturation of the visual cortex.     

Gabaergic NADPH-diaphorase-positive Martinotti cells in the visual cortex in rats]

NADPH-diaphorase positive cells were described in the visual cortex of the rat in layers II-VI and in the white matter. Their somata were large or medium-sized, oval or elongated, and their cytoplasm was accumulated at the poles. Some proximal thickened coarse dendrites formed a bitufted dendritic field. These features showed a cell type impregnated with the Golgi-Kopsch-method and a Golgi-deimpregnation-method described as Martinotti cell (sparsely spined polarized neurons with ascending axons). The immunocytochemical evidence of GABA in NADPH-diaphorase positive neurons (double labeling) showed the GABA ergic nature of these cells, but an attempt for a double labelling of NADPH-diaphorase and Parvalbumin was negative.     

Spatially opponent excitation and inhibition in simple cells of the cat visual cortex

The receptive fields of simple cells in the cat visual cortex are, by definition, divided into ON and OFF subfields. There is little doubt that each subfield is generated by excitatory input from geniculate neurons of the appropriate center type: ON subfields by ON-center cells, and OFF subfields by OFF-center cells. In intracellular records, ON subfields can be detected as regions in which light elicits a barrage of EPSPs, while in OFF subfields, turning a light off does the same. In addition, visual stimuli can evoke strong IPSPs, but these IPSPs have a receptive field spatially opponent to that of the EPSPs: Inhibition is evoked by turning a light off in an ON region and turning a light on in an OFF region. This inhibition probably arises from other cortical simple cells, and may contribute to such receptive-field properties as antagonism between subfields, binocular disparity sensitivity, and orientation selectivity.     

Suppression of perception in migraine: evidence for reduced inhibition in the visual cortex

BACKGROUND: Results from transcranial magnetic stimulation (TMS) studies of visual cortex have confirmed visual cortical hyperexcitability in patients with migraine. It has been speculated that this may be due to deficient intracortical inhibitory tone. However, the TMS induction of phosphenes relies on the reporting of a subjective experience, and may thus be subject to bias. METHODS: Seven migraineurs with visual aura and seven sex- and age-matched controls were studied. Fifty-four different three-letter combinations were briefly displayed and followed by a magnetic pulse at 40, 70, 100, 130, 160, and 190 msec. Subjects were required to report as many letters as they thought they had recognized. RESULTS: In the migraine group, the mean proportion of correctly identified letters was significantly higher at 100 msec, as was the proportion of trials with two or three letters correctly reported. The time window in which perceptual suppression could be introduced was narrower in migraineurs compared to controls. CONCLUSION: These findings suggest that inhibitory systems are activated to a lesser extent by TMS pulses in patients. This observation is in agreement with the hypothesized deficiency of intracortical inhibition of the visual cortex, at least in migraineurs with aura.     

Quantitative architectonic variations in the visual cortex of mice following varying light exposure of the visual organ]

Quantitative - architectural investigations were carried through with two experimental groups of white mice. One group was expsed to a source of light day and night, the other group lived under normal light variations. The animals of both groups were already born under the mentioned conditions and killed in etherization after 51 days. After the determination of the brain-weights, which showed smaller quantities for the group living under light day and night, sections of 10 mum were stained according to the NISSL method and the thickness of the cortex was measured. The layers in the area striata were examined with regard to possible differences. But in this connection no differences between the two groups were to be found. According to the point - method the different coefficients of the cortical layers were determined. The mathematical - statistical analysis with the help of t-test showed significantly bigger coefficients with the latter group (living under light day and night). These coefficients correspond to a smaller part of volume of neurons or their components in a defined volume. This way it was proved that changed light conditions result in changes of the microscopical structure of the area striata. At the same time significant changes occur in the nucleus-plasma-relation of the various layers. These make us recognize the functional adaptations to the changed environmental influences.     

Neuroregeneration in the visual cortex

Totally three articles focusing on the expression of Nogo-A, Nogo receptor and NADPH-diaphorase in the developing rat visual cortex and the effects of levodopa methyl ester on nerve growth factor expression in visual cortex area 17 in strabismic amblyopia are     

Acetylcholine-induced inhibition in the cat visual cortex is mediated b7 a GABAergic mechanism

The influence of iontophoretically applied acetylcholine (ACh) on single-unit activity in the visual cortex was studied in anesthetized cats. The dominant effect consisted of a slow facilitation of neuronal responses to moving light bars. This cholinergic action was sometimes paralleled by a decrease of the cells' selectivity to the direction of stimulus movement. In about one-third of the neurons studied ACh-iontophoresis suppressed maintained and visually driven activity within a few hundred milliseconds from the onset of its application. This effect was antagonized by concurrent iontophoresis of the muscarinic ACh-receptor antagonist scopolamine and the GABAA-receptor antagonist bicuculline methiodide. In 7% of the units studied a fast excitation was elicited by ACh application showing a similar time course as the rapid suppressive effect. It is concluded that ACh-induced inhibition is mediated by an activation of GABAergic interneurons. The role of cholinergic depression and facilitation in cortical information processing is discussed.     

Spatial inhibition and the visual cortex: a magnetic resonance spectroscopy imaging study

Introduction

Deficits in processing spatial information have been observed in clinical populations who have abnormalities within the dopamine (DA) system. As psychostimulants such as methamphetamine (MA) are particularly neurotoxic to the dopaminergic system it was of interest to examine the performance of MA-dependent individuals on a task of spatial attention.

Method

51 MA-dependent subjects and 22 age-matched non-substance abusing control subjects were tested on a Spatial Stroop attention test. MR Spectroscopy (MRS) imaging data were analyzed from 32 MA abusers and 13 controls.

Results

No group differences in response time or accuracy emerged on the behavioral task with both groups exhibiting equivalent slowing when the word meaning and the spatial location of the word were in conflict. MRS imaging data from the MA abusers revealed a strong inverse correlation between NAA/Cr ratios in the Primary Visual Cortex (PVC) and spatial interference (p = 0.0001). Moderate inverse correlations were also seen in the Anterior Cingulate Cortex (ACC) (p = 0.02). No significant correlations were observed in the controls, perhaps due to the small sample of imaging data available (n = 13).

Discussion

The strong correlation between spatial conflict suppression and NAA/Cr levels within the PVC in the MA-dependent individuals suggests that preserved neuronal integrity within the PVC of stimulant abusers may modulate cognitive mechanisms that process implicit spatial information.     

Microionophoretic study of the cholinoceptor neurons of the visual cortex of cats]

The optic cortex unit responses to the microionophoretic acetylcholine application were studied in acute experiments on unanesthetized cats restrained with diplacine. Of total amount of registered units 59% were sensitive to acetylcholine and revealed excitative (predominantly) or inhibitory responses.     

Synchronisation hubs in the visual cortex may arise from strong rhythmic inhibition during gamma oscillations

Neurons in the visual cortex exhibit heterogeneity in feature selectivity and the tendency to generate action potentials synchronously with other nearby neurons. By examining visual responses from cat area 17 we found that, during gamma oscillations, there was a positive correlation between each unit's sharpness of orientation tuning, strength of oscillations, and propensity towards synchronisation with other units. Using a computational model, we demonstrated that heterogeneity in the strength of rhythmic inhibitory inputs can account for the correlations between these three properties. Neurons subject to strong inhibition tend to oscillate strongly in response to both optimal and suboptimal stimuli and synchronise promiscuously with other neurons, even if they have different orientation preferences. Moreover, these strongly inhibited neurons can exhibit sharp orientation selectivity provided that the inhibition they receive is broadly tuned relative to their excitatory inputs. These results predict that the strength and orientation tuning of synaptic inhibition are heterogeneous across area 17 neurons, which could have important implications for these neurons' sensory processing capabilities. Furthermore, although our experimental recordings were conducted in the visual cortex, our model and simulation results can apply more generally to any brain region with analogous neuron types in which heterogeneity in the strength of rhythmic inhibition can arise during gamma oscillations.     

Three-dimensional visual feature representation in the primary visual cortex

In the cat primary visual cortex, it is accepted that neurons optimally responding to similar stimulus orientations are clustered in a column extending from the superficial to deep layers. The cerebral cortex is, however, folded inside a skull, which makes gyri and fundi. The primary visual area of cats, area 17, is located on the fold of the cortex called the lateral gyrus. These facts raise the question of how to reconcile the tangential arrangement of the orientation columns with the curvature of the gyrus.In the present study, we show a possible configuration of feature representation in the visual cortex using a three-dimensional (3D) self-organization model. We took into account preferred orientation, preferred direction, ocular dominance and retinotopy, assuming isotropic interaction. We performed computer simulation only in the middle layer at the beginning and expanded the range of simulation gradually to other layers, which was found to be a unique method in the present model for obtaining orientation columns spanning all the layers in the flat cortex. Vertical columns of preferred orientations were found in the flat parts of the model cortex. On the other hand, in the curved parts, preferred orientations were represented in wedge-like columns rather than straight columns, and preferred directions were frequently reversed in the deeper layers. Singularities associated with orientation representation appeared as warped lines in the 3D model cortex. Direction reversal appeared on the sheets that were delimited by orientation-singularity lines. These structures emerged from the balance between periodic arrangements of preferred orientations and vertical alignment of the same orientations. Our theoretical predictions about orientation representation were confirmed by multi-slice, high-resolution functional MRI in the cat visual cortex. We obtained a close agreement between theoretical predictions and experimental observations. The present study throws a doubt about the conventional columnar view of orientation representation, although more experimental data are needed.     

Participation of hypothalamic formations in regulation of the neuronal activity of rabbit visual cortex]

Electric stimulation of different hypothalamic nuclei was used during the effect of extracellular polarizing current on neurons of the rabbit optic cortex. It was found that stimulation of the hypothalamus caused a decrease in the medium rate of impulsation of a great number of studied optic cortex neurons under conditions of anodic polarization when the background level of activity was considerably enhanced. The same stimulation increased the activity under conditions of cathodic polarization when the initial level of the activity was considerably lowered. The same tendency to restore the initial (background) level of the neuronal activity after hypothalamic stimulation was observed under conditions when this level was shifted by application of rhythmic light. The greatest effect was observed during stimulation of the preoptic region. Stimulation of the posterior hypothalamic nucleus was less effective in this respect.     

Interconnections of the visual cortex with the frontal cortex in the rat

Horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) and autoradiography of tritiated leucine were used to trace the cortical origins and terminations of the connections between the visual and frontal cortices in the rat. Ipsilateral reciprocal connections between each subdivision of the visual cortex (areas 17, 18a and 18b) and the posterior half of the medial part of the frontal agranular cortex (PAGm), and their laminar organizations were confirmed. These connections did not appear to have a significant topographic organization. Although in areas 17 and 18b terminals or cells of origin in this fiber system were confined to the anterior half of these cortices, in area 18a they were observed spanning the anteroposterior extent of this cortex, with in part a column like organization. No evidence could be found for the participation of both the posterior parts of areas 17 and 18b and the anterior half of this frontal agranular cortex in these connections. Fibers from each subdivision of the visual cortex to the PAGm terminated predominantly in the lower part of layer I and in layer II. In area 17, this occipito-frontal projection was found to arise from the scattered pyramidal cells in layer V and more prominently from pyramidal cells in layer V of area 17/18a border. In area 18a, the fibers projecting to the PAGm originated mainly from pyramidal cells primarily in layer V and to a lesser extent in layers II, III and VI. Whereas in area 18b, this projection was found to arise mainly from pyramidal cells in layers II and III, to a lesser extent in layers V and VI, and less frequent in layer IV. On the other hand, the reciprocal projection to the visual cortex was found to originate largely from pyramidal cells in layers III and V of the PAGm. In areas 17 and 18a, these fibers terminated in layers I and VI, and in layers I, V and VI, respectively. Whereas in area 18b, they were distributed throughout all layers except layer II.