Tiande Shou

ORIENTATION BIAS OF THE EXTRACLASSICAL RECEPTIVE FIELD OF THE RELAY CELLS IN THE CAT'S DORSAL LATERAL GENICULATE NUCLEUS

The spatial properties of the extraclassical receptive fields (ECRF) of neurons responding to a stimulus restricted to it and its interaction with the classical receptive field (CRF) in visual information processing were investigated in 74 relay cells in the dorsal lateral geniculate nucleus (LGNd) of anesthetized cats. The results demonstrate that the ECRF of most relay cells in the LGNd responded preferentially to a grating stimulus of low spatial frequency through a mechanism of spatial summation. These biased cells showed a significant orientation bias which was relatively smaller than that of the CRF. The preferred orientations of the ECRF were not correlated with those of the CRF in most relay cells. The orientation biased ECRFs and CRFs interacted with each other in a non-linear way, resulting in a great diversity of response properties. Overall, the CRF played a more significant role than the ECRF in determining a cells orientation bias and preferred orientation. The ECRF mostly showed a modulatory role mainly in suppressing and/or in partially facilitating the neural response to stimulation in the CRF although in some cases, the ECRF did determine a cells responsiveness and orientation sensitivity. These results suggest that the ECRF might contribute to the ability of the LGNd neurons to detect some complex features such as texture segmentation and provide a subcortical contribution to the integrative field of visual cortical cells through receiving inputs from retinal ganglion cells with similar orientation biased extended surrounds [Neuroscience 98 (2000) 207].

Transhemispheric functional reorganization of the motor cortex induced by the peripheral contralateral nerve transfer to the injured arm

Peripheral nerve injury in a limb usually causes functional reorganization of the contralateral motor cortex. However, a dynamic process of the novel transhemispheric functional reorganization in the motor cortex was found in adult rats after transferring the seventh cervical nerve root from the contralateral healthy side to the injured limb. Initially the ipsilateral motor cortex activated the injured forepaw for 5 months after the operation. Then, both hemispheres of the cortex activated the injured forepaw, and finally the contralateral cortex exclusively controlled the injured forepaw. It is concluded an extensive functional shift occurred between two hemispheres based on neural plasticity in the CNS. The experimental results of the later lesions of the ipsilateral cortex suggest that maintaining transhemispheric functional reorganization does not depend on the corpus callosum, but depends on mechanisms involving central axonal sprouting. Possible mechanisms underlying the alternative changes in cortical functions were discussed in rats and in patients having similar operations.

Enhancement of oblique effect in the cat’s primary visual cortex via orientation preference shifting induced by excitatory feedback from higher-order cortical area 21a

It is often suggested that the oblique effect, the well-known phenomenon whereby both humans and animals are visually more sensitive to vertical and horizontal contours than to oblique ones, is due to the overrepresentation of cardinal orientations in the visual cortex. The functional role of feedback projections from higher-order cortical areas to lower-order areas is not fully understood. Combining the two issues in a study using optical imaging here, we report that the neural oblique effect was significantly enhanced (3.7 times higher than the normal) in the cats primary visual cortex through orientation shifting induced by excitatory feedback from the higher-order cortical area 21a. This suggests that a reciprocal co-excitatory mechanism may underlie the perceptual oblique effect.

Neuroprotective effect of transcorneal electrical stimulation on ischemic damage in the rat retina

Some previous studies have showed that transcorneal electrical stimulation (TES) could protect retinal neurons in certain rodent models. However, it is not yet clear whether TES could also definitely protect retinal neurons against ischemic insults. In the present study, we hypothesized that TES had such a neuroprotective effect and further investigated its underlying mechanism. Adult female Sprague-Dawley (SD) rats received TES treatment every other day after ocular ischemia was induced by elevating the intraocular pressure to 120 mm Hg for 60 min. Retinal ganglion cells (RGCs) were labeled retrogradely 7 days before ischemia and were counted 7 and 14 days later. At the same time points, retinal function was assessed by scotopic electroretinography (ERG), combined with retinal histological analysis. The glutamine synthetase (GS) immunoreactivity was compared between ischemic retinas with TES and those with sham stimulation under identical confocal laser microscope conditions. The immunohistochemical indications were confirmed by Western blot analysis. Higher mean density of RGCs was quantified in TES treated retinas compared to retinas with sham stimulation on days 7 and 14 after ischemia. Similarly, histological analysis showed that TES better preserved the mean thickness of separate retinal layers. ERG studies indicated that by undergoing TES treatment, the b-wave amplitude was also significantly preserved on day 7 after ischemia and recovered robustly on day 14. Immunohistochemical and Western blot analysis both revealed that GS levels remarkably increased after TES and lasted for at least 7 days. Our results indicate that TES can protect retinal neurons against ischemic insults, probably related to increasing levels of GS localized in Müller cells. These findings suggest a new approach for potential clinical application to ocular ischemic diseases.

COMPARATIVE STUDY ON THE OFFSET RESPONSES OF SIMPLE CELLS AND COMPLEX CELLS IN THE PRIMARY VISUAL CORTEX OF THE CAT

Simple and complex cells are two basic and distinct functional types of neurons in the mammalian primary visual cortex. Here, we studied the onset response and the offset response of simple and complex cells to a flashing visual stimulus in the cats area 17. Compared with simple cells, complex cells exhibited greater similarity between the onset and offset responses in peak latency. For simple cells, onset response had greater peak amplitude and signal-to-noise ratio than offset response, and for complex cells, vice versa. For both types of cortical cells, the amplitude of offset responses increased with stimulus duration within 100 ms significantly, while the onset response did not. However, to elicit a detectable offset response, complex cells tended to require shorter stimulus duration than simple cells did. In regard to the similarity of psychophysical data, these results suggest that the rebound offset response of cortical cells to disappearance of a visual pattern might be correlated to visual persistence in humans.

Quantitative analysis of brain optical images with 2D C0 complexity measure

Optical imaging based on intrinsic signals is a powerful method to visualize the activities of neural assembly in the cortex of animals in vivo, especially the detailed functional architecture of the visual cortex. Here, a new index, two-dimensional (2D) C0 complexity has been used to give a quantitative measure of the spatial pattern of the neural activity in orientation maps optically recorded from the visual cortex of cats globally. Results show that 2D C0 complexity could be employed to reveal the dynamic process of generating an orientation map in the visual cortex, and describe the variance of the neural responses in cortical area 17 under high and normal intraocular pressure. This suggests that 2D C0 could be used as a new quantitative measure for analyzing the intrinsic signal optical images.