Development of global visual processing: From the retina to the perceptive field.

Young children exhibit poorer visual performance than adults due to immaturity of the fovea and of the fundamental processing of visual functions such as masking and crowding. Recent studies suggest that masking and crowding are closely related to the size of the fundamental processing unit-the perceptive field (PF). However, while it is known that the retina and basic visual functions develop throughout childhood, it is not clear whether and how changes in the size of the PF affect masking and crowding. Furthermore, no retinal and perceptual development data have been collected from the same cohort and time. Here we explored the developmental process of the PF and the basic visual functions. Psychophysical and imaging methods were used to test visual functions and foveal changes in participants ranging from 3-17 years old. Lateral masking, crowding and contrast sensitivity were tested using computerized tasks. Foveal measurements were obtained from spectral-domain optical coherence tomography (OCT). The children patterns below 6 years exhibited high crowding, while the expected facilitation was found only at a larger target-flanker distance than required for children above 6 years, who exhibited the typical adult. Foveal thickness and macular volume for the children below 6 years were significantly lower than for the older group. Significant correlation was found for contrast sensitivity, foveal thickness and macular volume with age and between contrast sensitivity and foveal thickness. Our data suggest that the developmental processes at the retina and visual cortex occur in the same age range. Thus, in parallel to maturation of the PF, which enables reduction in crowding, foveal development contributes to increasing contrast sensitivity.

Intracranial electrode implantation produces regional neuroinflammation and memory deficits in rats.

Deep brain stimulation (DBS) is an established treatment for advanced Parkinson's disease (PD). The procedure entails intracranial implantation of an electrode in a specific brain structure followed by chronic stimulation. Although the beneficial effects of DBS on motor symptoms in PD are well known, it is often accompanied by cognitive impairments, the origin of which is not fully understood. To explore the possible contribution of the surgical procedure itself, we studied the effect of electrode implantation in the subthalamic nucleus (STN) on regional neuroinflammation and memory function in rats implanted bilaterally with stainless steel electrodes. Age-matched sham and intact rats were used as controls. Brains were removed 1 or 8 weeks post-implantation and processed for in vitro autoradiography with [(3)H]PK11195, an established marker of microglial activation. Memory function was assessed by the novel object recognition test (ORT) before surgery and 2 and 8 weeks after surgery. Electrode implantation produced region-dependent changes in ligand binding density in the implanted brains at 1 as well as 8 weeks post-implantation. Cortical regions showed more intense and widespread neuroinflammation than striatal or thalamic structures. Furthermore, implanted animals showed deficits in ORT performance 2 and 8 weeks post-implantation. Thus, electrode implantation resulted in a widespread and persistent neuroinflammation and sustained memory impairment. These results suggest that the insertion and continued presence of electrodes in the brain, even without stimulation, may lead to inflammation-mediated cognitive deficits in susceptible individuals, as observed in patients treated with DBS.

Enhancing the contrast sensitivity function through action video game training.

The contrast sensitivity function (CSF) is routinely assessed in clinical evaluation of vision and is the primary limiting factor in how well one sees. CSF improvements are typically brought about by correction of the optics of the eye with eyeglasses, contact lenses or surgery. We found that the very act of action video game playing also enhanced contrast sensitivity, providing a complementary route to eyesight improvement.