Temporal Sequence of Visuo-Auditory Interaction in Multiple Areas of the Guinea Pig Visual Cortex

Recent studies in humans and monkeys have reported that acoustic stimulation influences visual responses in the primary visual cortex (V1). Such influences can be generated in V1, either by direct auditory projections or by feedback projections from extrastriate cortices. To test these hypotheses, cortical activities were recorded using optical imaging at a high spatiotemporal resolution from multiple areas of the guinea pig visual cortex, to visual and/or acoustic stimulations. Visuo-auditory interactions were evaluated according to differences between responses evoked by combined auditory and visual stimulation, and the sum of responses evoked by separate visual and auditory stimulations. Simultaneous presentation of visual and acoustic stimulations resulted in significant interactions in V1, which occurred earlier than in other visual areas. When acoustic stimulation preceded visual stimulation, significant visuo-auditory interactions were detected only in V1. These results suggest that V1 is a cortical origin of visuo-auditory interaction.     

Bilateral sensory disturbance after cortical spreading depression revealed by fluorescence imaging of voltage‐sensitive dye

Cortical spreading depression (CSD), a propagation wave of transient neuronal and glial depolarization followed by suppression of spontaneous brain activity, has been hypothesized to be the underlying mechanism of migraine aura and triggers the headache attack. Evidence from various animal models accumulates since its first discovery in 1944 and provides support for this hypothesis. In this paper, alterations of bilateral cortical responses are investigated in a mice migrainous model of CSD using voltage‐sensitive dye imaging under hindlimb and cortical stimulation. After CSD induction in the right hemisphere, bilateral sensory responses evoked by left hindlimb stimulation dramatically decreases, whereas right hindlimb stimulation can still activate bilateral responses with an increased response of the left hemisphere and a well‐preserved response of the right hemisphere. In addition, cortical neural excitability remains after CSD assessed by direct activation of the right hemisphere in spite of the sensory deficit under contralateral hindlimb stimulation. These results depict the sensory disturbance of bilateral hemispheres after CSD, which may be helpful in understanding how sensory disturbance occur during migraine aura.      

Neuronal assemblies: single cortical neurons are obedient members of a huge orchestra

Spontaneous cortical activity of single neurons is often either dismissed as noise, or is regarded as carrying no functional significance and hence is ignored. Our findings suggest that such concepts should be revised. We explored the coherent population activity of neuronal assemblies in primary sensory area in the absence of a sensory input. Recent advances in real-time optical imaging based on voltage-sensitive dyes (VSDI) have facilitated exploration of population activity and its intimate relationship to the activity of individual cortical neurons. It has been shown by in vivo intracellular recordings that the dye signal measures the sum of the membrane potential changes in all the neuronal elements in the imaged area, emphasizing subthreshold synaptic potentials and dendritic action potentials in neuronal arborizations originating from neurons in all cortical layers whose dendrites reach the superficial cortical layers. Thus, the VSDI has allowed us to image the rather illusive activity in neuronal dendrites that cannot be readily explored by single unit recordings. Surprisingly, we found that the amplitude of this type of ongoing subthreshold activity is of the same order of magnitude as evoked activity. We also found that this ongoing activity exhibited high synchronization over many millimeters of cortex. We then investigated the influence of ongoing activity on the evoked response, and showed that the two interact strongly. Furthermore, we found that cortical states that were previously associated only with evoked activity can actually be observed also in the absence of stimulation, for example, the cortical representation of a given orientation may appear without any visual input. This demonstration suggests that ongoing activity may also play a major role in other cortical function by providing a neuronal substrate for the dependence of sensory information processing on context, behavior, memory and other aspects of cognitive function.     

利用激光扫描共聚焦显微镜研究视皮层脑片长时程增强过程中核酸的变化

本文使用 1 5— 2 0天龄幼年大鼠视皮层脑片的标本 ,在通氧状态下 ,用荧光探针 AO染色 ,激光扫描共聚焦显微镜对全脑片不同层面进行共聚焦断层扫描 ,沿纵轴每 2 0μm扫一次 ,共扫描 1 6次。再利用总值方式的投影算法对其三维重建 ,分析幼年大鼠视皮层脑片长时程增强过程中核酸的变化。     

用脑光学成像精确测定猫初级视皮层视野拓扑投射关系

利用基于脑内源信号的光学成像和二维互相关分析的方法,对猫初级视皮层17区的视野拓扑离心度(即视网膜-皮层拓扑关系)进行了精确测量。当采用在同一屏幕内处于上下视野的、方位互相垂直的两个相邻光栅刺激时,皮层中一部分区域的绝大部分细胞因同时兴奋而导致方位功能图模糊不清。将这种方位功能图和用单一方位(水平或垂直)全屏光栅刺激所得到的功能图进行比较,通过计算每一像素的互相关系数,从而获得皮层的精确视野拓扑离心度。同时用电生理的方法测量了同一视皮层内的单细胞的感受野位置,证明这种方法得到的视野离心度和光学记录方法得到的相同。因此,本研究为大面积地确定视皮层细胞感受野在视野中的位置提供了一种快速和较准确的方法。     

Multi‐wavelength light emitting diode‐based disposable optrode array for in vivo optogenetic modulation

We present a light emitting diode (LED)‐based optical waveguide array that can optogenetically modulate genetically targeted neurons in the brain. The reusable part of the system consists of control electronics and conventional multi‐wavelength LED. The disposable part comprises optical fibers assembled with microlens array fabricated on a silicon die. Both parts can be easily assembled and separated by snap fit structure. Measured light intensity is 3.35 mW/mm² at 469 nm and 0.29 mW/mm² at 590 nm when the applied current is 80 mA. In all the tested conditions, the light‐induced temperature rise is under 0.5°C and over 90% of the relative light intensity is maintained at 2 mm‐distance from the fiber tips. We further tested the efficiency of the optical array in vivo at 469 nm. When the optical array delivers light stimulation on to the visual cortex of a mouse expressing channelrhodopsin‐2, the neural activity is significantly increased. The light‐driven neural activity is successfully transformed into a percept of the mouse, showing significant learning of the task detecting the cortical stimulation. Our results demonstrate that the proposed optical array interfaces well with the neural circuits in vivo and the system is applicable to guide animal behaviors.      

The organization of somatosensory cortex in the short-tailed opossum (Monodelphis domestica)

The organization of neocortex in the short-tailed opossum (Monodelphis domestica) was explored with multiunit microelectrode recordings from middle layers of cortex. Microelectrode maps were subsequently related to the chemoarchitecture of flattened cortical preparations, sectioned parallel to the cortical surface and processed for either cytochrome oxidase (CO) or NADPH-diaphorase (NADPHd) histochemistry. The recordings revealed the presence of at least two systematic representations of the contralateral body surface located in a continuous strip of cortex running from the rhinal sulcus to the medial wall. The primary somatosensory area (S1) was located medially while secondary somatosensory cortex (S2) formed a laterally located mirror image of S1. Auditory cortex was located in lateral cortex at the caudal border of S2, and some electrode penetrations in this area responded to both auditory and somatosensory stimulation. Auditory cortex was outlined by a dark oval visible in flattened brain sections. A large primary visual cortex (V1) was located at the caudal pole of cortex, and also consistently corresponded to a large chemoarchitecturally visible oval. Cortex just rostral and lateral to V1 responded to visual stimulation, while bimodal auditory/visual responses were obtained in an area between V1 and somatosensory cortex. The results are compared with brain organization in other marsupials and with placentals and the evolution of cortical areas in mammals is discussed.     

The area of the optically activated zones of cat area 17 under stimulation with grids of different orientation

In acute experiments with 9 anesthetized and immobilized cats, the relative tangential square of the activated cortical columns in area 17 was mapped by the intrinsic optical signal under stimulation with grids of different orientation. We examined the "oblique effect", i.e. the greater representation of neurons tuned to the vertical and horizontal orientations vs. oblique orientations in the primary visual cortex. The square of the activated parts of the cortex was estimated under different threshold criteria (80, 60 and 40% of the maximum). The "oblique effect" was not observed in our study: the areas of activation of the cortical columns did not differ statistically for two basic vs. oblique orientations. Reasons for the difference between the results of electrophysiological and optical mapping are suggested and possible contributions of the experimental protocol (anesthesia) and individual visual experience in different animals' samples to the origin of these differences are discussed.     

The organization of somatosensory cortex in the short-tailed opossum ( Monodelphis domestica )

The organization of neocortex in the short-tailed opossum ( Monodelphis domestica ) was explored with multiunit microelectrode recordings from middle layers of cortex. Microelectrode maps were subsequently related to the chemoarchitecture of flattened cortical preparations, sectioned parallel to the cortical surface and processed for either cytochrome oxidase (CO) or NADPH-diaphorase (NADPHd) histochemistry. The recordings revealed the presence of at least two systematic representations of the contralateral body surface located in a continuous strip of cortex running from the rhinal sulcus to the medial wall. The primary somatosensory area (S1) was located medially while secondary somatosensory cortex (S2) formed a laterally located mirror image of S1. Auditory cortex was located in lateral cortex at the caudal border of S2, and some electrode penetrations in this area responded to both auditory and somatosensory stimulation. Auditory cortex was outlined by a dark oval visible in flattened brain sections. A large primary visual cortex (V1) was located at the caudal pole of cortex, and also consistently corresponded to a large chemoarchitecturally visible oval. Cortex just rostral and lateral to V1 responded to visual stimulation, while bimodal auditory/visual responses were obtained in an area between V1 and somatosensory cortex. The results are compared with brain organization in other marsupials and with placentals and the evolution of cortical areas in mammals is discussed.     

Functional organization of afferent inputs of neurons of the cat somatic cortex

Responses of cortical neurons in the posterior sigmoid gyrus to stimulation of two points of the ventro-posterolateral nucleus were investigated in cats immobilized with D-tubocurarine. Some neurons responding to stimulation of one point of this nucleus with a latent period of 2.5–4 msec, were activated by stimulation of the other point after 10 msec or longer. Conditioning stimulation of one point facilitated or inhibited the response to test stimulation of the other point. The facilitatory effect was usually exhibited if the response latency exceeded 5 msec. It is concluded that a cortical input neuron for some afferent fibers is activated by other similar afferent fibers only after intracortical relay. The system of "input" cortical neurons is thus not only a structural, but also to some extent a functional, concept; under certain conditions an incoming afferent volley activates them only polysynaptically.     

The combined activities of the temporal cortical area and hippocampus in man during the localization of a moving sound image

In patients with epileptic lesions in the cortex and mediobasal structures of the brain, studies have been made on the perception of spatial position of sound images during dichotic stimulation. It was established that the extreme interval which is necessary for formation of sensation of the moving sound image increases during right-side lesions of the temporal cortex. During left-side lesion of the temporal lobe, more diffuse disturbances in the trajectory of image movement (from the right and left) are observed, whereas right-side lesions result in disturbances of movement only at the opposite side of the latter. Cortical lesions and those in the mediobasal parts of the temporal lobe are accompanied by identical gradient of disturbances in the trajectory of sound image movement and short-term imprinting of succession of signals which differ with respect to their spatial position. Maximum disturbances are observed during lesions in the cortical and mediobasal parts of the temporal lobe, whereas only cortical lesions or only hippocampal lesions result in less significant disturbances. It is suggested that combined activity of the auditory cortex and hippocamp is necessary for localization of a sound source.     

Mechanisms of amoeboid chemotaxis: an evaluation of the cortical expansion model

In this work we evaluate the cortical expansion model for amoeboid chemotaxis with regard to new information about molecular events in the cytoskeleton following chemotactic stimulation of Dictyostelium amoebae. A rapid upshift in the concentration of chemoattractant can be used to synchronize the motile behavior of a large population of cells. This synchrony presents an opportunity to study the biochemical basis of morphological changes such as pseudopod extension that are required for amoeboid chemotaxis. Changes in the composition and activity of the cytoskeleton following stimulation can be measured with precision and correlated with important morphological changes. Such studies demonstrate that activation of actin nucleation is one of the first and most crucial events in the actin cytoskeleton following stimulation. This activation is followed by incorporation of specific actin cross-linking proteins into the cytoskeleton, which are implicated in the extension of pseudopods and filopods. These results, as well as those from studies with mutants deficient in myosin, indicate that cortical expansion, driven by focal actin polymerization, cross-linking and gel osmotic swelling, is an important force for pseudopod extension. It is concluded that whereas three forces, frontal sliding, tail contraction, and cortical expansion may cooperate to produce amoeboid movement, the cortical expansion model offers the simplest explanation of how focal stimulation with a chemoattractant causes polarized pseudopod extension.     

Axonal processes and neural plasticity. III. Competition for dendrites.

In previous work we have developed a computational framework for topographic map formation and plasticity based on axonal process sprouting and retraction, in which sprouting and retraction are governed by competition for neurotrophic support. Here we show that such an approach can account for certain aspects of the dendritic morphology of cortical maps. In particular, we model the development of ocular dominance columns in the primary visual cortex and show that cortical cells near to column boundaries prefer to elaborate dendritic fields which avoid crossing the boundaries. This emerges as different functional inputs are spatially separated. We predict that afferent segregation occurs before or simultaneously with, but not after, the emergence of dendritic bias. We predict that animals reared with complete but asynchronous stimulation of the optic nerves do not develop a dendritic bias. We suggest that the emergence of a dendritic bias might provide a partial account for the critical period for a response to monocular deprivation. In particular, we predict that animals reared with asynchronous optic nerve stimulation might exhibit an extended critical period. Our results also indicate that the number of synapses supported by cortical cells depends on the intra-ocular image correlations used in our simulations. This suggests that inter-ocular image correlations, and thus strabismic rearing of kittens, may also affect the innervation density.     

Corticofugal factors in the development of feeding motivation]

The influences of various cortical areas in the mechanisms of feeding motivation, forming a directed response, were investigated in chronic experiments on rabbits. Electric stimulation of the frontal and antero-temporal cortical areas inhibited the feeding response elicited by the hypothalamic feeding centre stimulation. Inhibition of the frontal cortex proved to be more expressed. Stimulation of the postero-temporal and occipital cortical areas decreased the threshold of an evoked feeding response or elicited this response in the satiated animals.     

Noninvasive laser-induced photoacoustic tomography for structural and functional in vivo imaging of the brain

Imaging techniques based on optical contrast analysis can be used to visualize dynamic and functional properties of the nervous system via optical signals resulting from changes in blood volume, oxygen consumption and cellular swelling associated with brain physiology and pathology. Here we report in vivo noninvasive transdermal and transcranial imaging of the structure and function of rat brains by means of laser-induced photoacoustic tomography (PAT). The advantage of PAT over pure optical imaging is that it retains intrinsic optical contrast characteristics while taking advantage of the diffraction-limited high spatial resolution of ultrasound. We accurately mapped rat brain structures, with and without lesions, and functional cerebral hemodynamic changes in cortical blood vessels around the whisker-barrel cortex in response to whisker stimulation. We also imaged hyperoxia- and hypoxia-induced cerebral hemodynamic changes. This neuroimaging modality holds promise for applications in neurophysiology, neuropathology and neurotherapy.     

Activation and Inactivation of Mechanosensitive Currents in the Chick Heart

The behavior of MS channels in embryonic chick ventricular myocytes activated by direct mechanical stimulation is strongly affected by inactivation. The amplitude of the current is dependent not only on the amplitude of the stimulus, but also the history of stimulation. The MS current inactivation appears to be composed of at least two contributions: (i) rearrangement of the cortical tension transducing elements and (ii) blocking action of an autocrine agent released from the cell. With discrete mechanical stimuli, the MS current amplitude in the second press of a double press protocol was always smaller than the amplitude of the first MS current. Occasionally, a large MS current occurred when the cell was first stimulated, but subsequently the cell became unresponsive. For a series of stimuli of varying amplitudes, the order in which they were applied to the cell affected the size of the observed MS current for a given stimulus magnitude. When continuous sinusoidal stimulation was applied to the cells, the MS current envelope either reached a steady state, or inactivated. With sinusoidal stimulation, the MS response could be enhanced or restored by simple perfusion of fluid across the cell. This suggests that mechanical stimulation of the cells produces an autocrine inhibitor of MS channels as well as resulting in cortical rearrangement. Received: 7 July 1999/Revised: 26 October 1999     

Real Time Intraoperative Functional Brain Mapping Based on RGB Imaging

Intraoperative optical imaging is a localization technique for the functional areas of the human brain cortex during neurosurgical procedures. However, it still lacks robustness to be used as a clinical standard. In particular new biomarkers of brain functionality with improved sensitivity and specificity are needed. We present a method for the real time identification of the activated cortical areas based on the analysis of the cortical hemodynamic using a RGB camera and a white light source. We measure the quantitative oxy and deoxy-hemoglobin concentration changes in the human brain cortex with the modified Beer-Lambert law and Monte Carlo simulations. A functional model has been implemented to define in real time a binary biomarker of the cortical activation following neuronal activation by physiological stimuli. The results show a good correlation between the computed activation maps and the brain areas localized by electrical brain stimulation. We demonstrate that a RGB camera combined with a quantitative modeling of brain hemodynamics biomarkers can evaluate in real time the functional areas during neurosurgery and serve as a tool of choice to complement electrical brain stimulation.     

Protein synthesis-independent plasticity mediates rapid and precise recovery of deprived eye responses

Monocular deprivation (MD) for a few days during a critical period of development leads to loss of cortical responses to stimulation of the deprived eye. Despite the profound effects of MD on cortical function, optical imaging of intrinsic signals and single-unit recordings revealed that deprived eye responses and orientation selectivity recovered a few hours after restoration of normal binocular vision. Moreover, recovery of deprived eye responses was not dependent upon mRNA translation, but required cortical activity. Interestingly, this fast recovery and protein synthesis independence was restricted to the hemisphere contralateral to the previously deprived eye. Collectively, these results implicate a relatively simple mechanistic process in the reactivation of a latent set of connections following restoration of binocular vision and provide new insight into how recovery of cortical function can rapidly occur in response to changes in sensory experience.     

Hemodynamic changes in cortical sensorimotor systems following hand and orofacial motor tasks and pulsed pneumotactile stimulation

We performed a functional near-infrared spectroscopy (fNIRS) study of the evoked hemodynamic responses seen in hand and face sensorimotor cortical representations during (1) active motor tasks and (2) pulsed pneumotactile stimulation. Contralateral fNIRS measurements were performed on 22 healthy adult participants using a block paradigm that consisted of repetitive right hand and right oral angle somatosensory stimulation using a pulsed pneumotactile array stimulator, and repetitive right-hand grip compression and bilabial compressions on strain gages. Results revealed significant oxyhemoglobin (HbO) modulation across stimulus conditions in corresponding somatotopic cortical regions. Of the 22 participants, 86% exhibited a decreased HbO response during at least one of the stimulus conditions, which may be indicative of cortical steal, or hypo-oxygenation occurring in channels adjacent to the primary areas of activation. Across all conditions, 56% of participants’ HbO responses were positive and 44% were negative. Hemodynamic responses most likely differed across hand and face motor and somatosensory cortical regions due to differences in regional arterial/venous anatomy, cortical vascular beds, extent and orientation of somatotopy, task dynamics, and mechanoreceptor typing in hand and face. The combination of optical imaging and task conditions allowed for non-invasive examination of hemodynamic changes in somatosensory and motor cortices using natural, pneumatic stimulation of glabrous hand and hairy skin of the lower face and functionally relevant and measurable motor tasks involving the same structures.     

Excitability of the sensomotor cortex and red nucleus of rabbits at different levels of spatial synchronization of cortical potentials

To determine the excitability of the rabbit sensomotor cortex and red nucleus the animal's motor response to electrical stimulation of these structures at threshold strength was investigated. In computerized experiments the excitability of these structures was compared in situations characterized by different degrees of correlation of cortical potentials. An increase in the level of spatial synchronization of cortical potentials was shown to be accompanied by an increase in the excitability of the sensomotor cortex and red nucleus. This increase in excitability is evidently a neurophysiological mechanism of the increase in probability of appearance of an effector response to sensory stimulation when the level of spatial synchronization of cortical potentials is raised.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 19–24, January–February, 1977.