Binocular suppression in cortical neurons

Summary Dichoptic presentation of patterns similar in shape but of very different contrast results in the perception of only the high contrast pattern (binocular suppression). When recording from binocular neurons of the cat visual cortex, we have found an effect which is strikingly similar to this perceptual phenomenon. If a high and a low contrast grating are presented simultaneously, one to each eye, the cell's response to the low contrast stimulus is suppressed.     

Source-density mapping of human visual receptive fields using scalp electrodes

Summary A triangular array of 20 electrodes spaced by 1.5 cm was used to record the distribution of current source-densities at 12 locations over the occipital scalp, in response to tachistoscopic presentation of a 1/2° × 1/2° scanning pattern element which explored a 2° × 2° area of the visual field. Single scalp locations had visual receptive fields of the order of 1°–2° in diameter, their shape varying somewhat according to the response in question. Source density analysis can resolve details of the AEP scalp map to better than 1 cm. Even with a 1/2° × 1/2° stimulus, averages of only a few tens of sweeps gave adequate signal-to-noise ratios.     

位图在动态绘制肌电信号中的应用

鉴于常见的动态绘制肌电曲线时出现的屏幕闪烁和抖动问题 ,设计了在面向对象的VisualC 6 .0开发平台上 ,利用MFC(MicrosoftFoundationClasses)类库中的位图类CBitmap来绘制肌电曲线图像 ,解决肌电数据的动态回放和实时监测中的屏幕闪烁和抖动问题     

Role of vestibular and neck inputs for the perception of object motion in space

Summary The contribution of vestibular and neck inputs to the perception of visual object motion in space was studied in the absence of a visual background (in the dark) in normal human subjects (Ss). Measures of these contributions were obtained by means of a closed loop nulling procedure; Ss fixed their eyes on a luminous spot (object) and nulled its actual or apparent motion in space during head rotation in space (vestibular stimulus) and/ or trunk rotation relative to the head (neck stimulus) with the help of a joystick. Vestibular and neck contributions were expressed in terms of gain and phase with respect to the visuo-oculomotor/joystick feedback loop which was assumed to have almost ideal transfer characteristics. The stimuli were applied as sinusoidal rotations in the horizontal plane (f= 0.025–0.8 Hz; peak angular displacements, 1–16°). Results: (1) During vestibular stimulation, Ss perceived the object, when kept in fixed alignment with the moving body, as moving in space. However, they underestimated the object motion; the gain was only about 0.7 at 0.2–0.8 Hz and clearly decreased at lower stimulus frequencies, while the phase exhibited a small lead. (2) During pure neck stimulation (trunk rotating relative to the stationary head), the object, when stationary, appeared to move in space counter to the trunk excursion. This neck-contingent object motion illusion was small at 0.2–0.8 Hz, but increased considerably with decreasing frequency, while its phase developed a small lag. (3) Vestibular, neck, and visuo-oculomotor effects summed linearly during combined stimulations. (4) The erroneous vestibular and neck contributions to the object motion perception were complementary to each other, and the perception became about veridical (G1, 0°), when both inputs were combined during head rotation with the trunk stationary. The results are simulated by an extended version of a computer model that previously had been developed to describe vestibular and neck effects on human perception of head motion in space. In the model, the perception of object motion in space is derived from the superposition of three signals, representing object to head, (visuo-oculomotor; head coordinates), head on trunk (neck; trunk coordinates), and trunk in space (vestibular-neck interaction; space coordinates).Supported by Deutsche Forschungsgemeinschaft, SFB 325     

A Golgi deimpregnation study of neurons in the rhesus monkey visual cortex (Areas 17 and 18)

Summary The morhological features of 298 neurons impregnated according to Golgi-Kopsch in areas 17 and 18 of Macaca mulatta were analyzed, and the same neurons were deimpregnated to visualize structural details of the somata in different types of neurons. The following cell types were investigated: Pyramidal and pyramid-like cells, spiny stellate cells, double bouquet cells, bipolar cells, chandelier cells, neurogliaform cells, basket and related cells. This procedure allows the evaluation of the nuclear-cytoplasmic proportion and the position of the nucleus besides shape and size of the cell body. Pyramidal and pyramid-like cells (N=43), spiny stellate cells (N=26), basket and related cells (N=126) are variable in these features. A positive correlation between soma size and width of the cytoplasm is found in pyramidal, pyramid-like cells and spiny stellate cells. With the exception of some large somata in both these types of neurons the nucleus is found in a central position. Double bouquet cells (N=6), bipolar cells (N=13) and chandelier cells (N=11) exhibit small cytoplasmic rims and centrally located nuclei. The small somata of neurogliaform cells (N=37), however, and the small to very large somata of basket and related cells show broad cytoplasmic portions surrounding the eccentrically located nuclei. These findings allow the identification of different neuronal types in Nisslstained sections on the basis of these soma features. This is a prerequisite for further detailed quantitative studies on the laminar distribution of different neuronal types in the visual cortex of the monkey.     

Enhanced responsiveness of human extravisual areas to photic stimulation in patients with severely reduced vision

Lesions in the primary visual cortex induce severe loss of visual perception. Depending on the size of the lesion, the visual field might be affected by small scotomas, hemianopia, or complete loss of vision (cortical blindness). In many cases, the whole visual field of the patient is affected by the lesion, but diffuse light-dark discrimination remains (residual rudimentary vision, RRV). In other cases, a sparing of a few degrees can be found (severely reduced vision, SRV).In a follow-up study, we mapped visually induced cerebral activation of three subjects with SRV using functional magnetic resonance imaging. We were especially interested in the visual areas that would be activated if subjects could perceive the stimulus consciously although information flow from V1 to higher visual areas was strongly reduced or virtually absent. Because subjects were only able to discriminate strong light from darkness, we used goggles flashing intense red light at a frequency of 3 Hz for full visual field stimulation. Besides reduced activation in V1, we found activation in the parietal cortex, the frontal eye fields (FEF), and the supplementary eye fields (SEF). In all patients, FEF activation was pronounced in the right hemisphere. These patterns were never seen in healthy volunteers. In a patient who recovered completely, we observed that extrastriate activation disappeared in parallel with the visual field restitution. This result suggests that damage to the primary visual cortex changes the responsiveness of parietal and extravisual frontal areas in patients with SRV. This unexpected result might be explained by increased stimulus-related activation of attention-related networks.     

Visual discrimination learning in dwarf goats and associated changes in heart rate and heart rate variability

We studied visual discrimination learning in a group of Nigerian dwarf goats using a computer-based learning device which was integrated in the animals' home pen. We conducted three consecutive learning tasks (T1, T2 and T3), each of which lasted for 13 days. In each task, a different set of four visual stimuli was presented on a computer screen in a four-choice design. Predefined sequences of stimulus combinations were presented in a pseudorandom order. Animals were rewarded with drinking water when they chose the positive stimulus by pressing a button next to it. Noninvasive measurements of goats' heartbeat intervals were carried out on the first and the last 2 days of each learning task. We analysed heart rate (HR) and heart rate variability (HRV) of resting animals to study sustained physiological effects related to general learning challenge rather than acute excitement during an actual learning session. The number of trials to reach the learning criterion was 1000 in T1, when visual stimuli were presented to the goats for the first time, but decreased to 210 in T2 and 240 in T3, respectively. A stable plateau of correct choices between 70% and 80% was reached on Day 10 in T1, on Day 8 in T2 and on Day 6 in T3. We found a significant influence of the task and of the interaction between task and day on learning success. Whereas HR increased throughout T1, this relationship was inverted in T2 and T3, indicating different effects on the HR depending on how familiar goats were with the learning task. We found a significant influence of the task and the interaction between task and time within the task on HRV parameters, indicating changes of vagal activity at the heart. The results suggest that changes in HR related to learning were predominantly caused by a withdrawal of vagal activity at the heart. With regard to nonlinear processes in heartbeat regulation, increased deterministic shares of HRV indicated that the animals did not really relax until the end of T3. Comparing changes of HR and HRV in T3 and in a subsequent postexperiment (PE), we assume a positive effect of such cognitive challenges once the task had been learned by the animals.     

Morphology of visual callosal neurons with different locations,contralateral targets or patterns of development

In kittens, callosally projecting neurons were labeled by retrograde transport of FITC- (fluorescein isothiocyanate)- and TRITC- (tetramethylrhodamine isothiocyanate)-conjugated latex microspheres injected in two different visual areas (17, 17/18, 19, or postero-medial lateral suprasylvian; PMLS) at postnatal day 3. At postnatal day 57 more than 1200 labeled neurons in visual cortical areas were intracellularly injected with 3% lucifer yellow (LY) in perfusion-fixed slices of the contralateral hemisphere. The distribution of labeled neurons was charted, and LY-filled neurons were classified on the basis of their area and layer of location, and dendritic pattern. The dendritic arbors of 120 neurons were computer reconstructed. For the basal dendrites of supragranular pyramidal neurons a statistical analysis of number of nodes, internodal and terminal segment lengths, and total dendritic length was run relative to the area of location and axonal projection. Connections were stronger between homotopic than between heterotopic areas. Overall tangential and laminar distributions depended on the area injected. Qualitative morphological differences were found among callosally projecting neurons, related to the area of location, not to that of projection. In all projections from areas 17 and 18, pyramidal and spinous stellate neurons were found in supragranular layers. In contrast, spinous stellate neurons lacked in projections from area 19, 21a, PMLS and postero-lateral lateral suprasylvian (PLLS). In all areas, the infragranular neurons showed heterogeneous typology, but in PMLS no fusiform cells were found. Quantitative analysis of basal dendrites did not reveal significant differences in total dendritic length, terminal, or intermediate segment length among neurons in area 17 or 18, and this was related to whether they projected to contralateral areas 17–18 or PMLS. All injections produced exuberant labeling in area 17. No differences could be found between neurons in area 17 (with transient axons through the corpus callosum) and neurons near the 17/18 border (which maintain projections to the corpus callosum). In conclusion, morphology of callosally projecting neurons seems to relate more to intrinsic specificities in the cellular composition of each area than to the area of contralateral axonal projection or the fate of callosal axons.     

用于选择视觉的数据和智能控制神经网络系统(英文)

在这篇论文中,我们提出了用于选择视觉的数据和智能控制的动态网络系统的神经实现过程。模型由数个相互作用的子系统构成,用于不同的处理。所有的神经子系统与信息和控制流程的倒序和顺序紧密相关。     

Visual orientation in the rat: A dissociation of deficits following cortical and collicular lesions

Summary Rats with either bilateral ablations of superior colliculus, bilateral ablations of visual cortex, or sham operations were trained to run across a large arena towards a small illuminated target which varied in location from trial to trial. An impairment in this visually-guided running was apparent in the cortical group, but not in the collicular group. When, in a second experiment, the spatial relationships within the apparatus were changed by extending the entry-tunnel some distance into the arena, the running of the cortical group became even more impaired, while the collicular animals continued to run towards the targets under efficient visual control. In a third experiment, the effect of introducing a novel flashing light in various locations around the perimeter of the arena was investigated. It was found that unlike the other two groups, the collicular animals showed no orienting reflex to the novel stimulus when it was presented outside a broad central area of the visual field.The authors acknowledge the financial support of the Science Research Council (grant no B/RG/61112)