Time/Room: Friday, May 10, 2013, 3:30 – 5:30 pm, Royal 1-3
Organizers: Susana Chung, University of California, Berkeley and Anthony Norcia, Stanford University
Presenters: Yuzo Chino, Lynne Kiorpes, Dennis Levi, Gunilla Haegerstrom-Portnoy
Many visual functions continue to develop and reach adult levels only in late childhood. The successful development of normal visual functions requires ‘normal’ visual experience. The speakers of this symposium will review the time courses of normal visual development of selected visual functions, and discuss the consequences of abnormal visual experience during development on these visual functions. The prospect of recovering visual functions in adults who experienced abnormal visual experience during development will also be discussed, along with the advances made in the assessment of visual functions in children with abnormal visual development due to damage to the visual cortex and the posterior visual pathways.
Postnatal development of early visual cortex in macaque monkeys
Speaker: Yuzo Chino, University of Houston
Our recent studies have demonstrated that the cortical circuitry supporting the monocular and binocular RF properties of V1 and V2 neurons in macaque monkeys is qualitatively adult like as early as 4 weeks of age, and, if not, by 8 weeks of age. However the functional organization of visual cortex in neonates and infants is fragile and needs ‘normal’ visual experience to complete its postnatal development. Experiencing binocular imbalance soon after birth disrupts this development and can result in binocular vision anomalies and often amblyopia. What happens to the visual brain of amblyopic subjects that experience early binocular imbalance is not well understood except for some aspects of early monocular form deprivation. This talk will present the results of studies in primate models of strabismic and anisometropic amblyopia, and make a proposal on how some of monocular deficits in amblyopes may develop. Our earlier studies established that binocular imbalance in infant monkeys immediately initiates interocular suppression in their visual cortex, which persists until adulthood. We also found that the depth of amblyopia in individual strabismic monkeys is highly correlated with the strength of binocular suppression in V1 and V2. I will present our preliminary data to demonstrate that such robust binocular suppression can disrupt the functional development of cortical circuits supporting the spatial map of subunits within the receptive field of a given V2 neuron in amblyopic monkeys, and also, suppression may affect the timing and reliability of spiking by these neurons.
Postnatal development of form and motion pathways in macaque monkeys
Speaker: Lynne Kiorpes, New York University
Many visual functions are poor in infant primates and develop to adult levels during the early months and years after birth. Basic visual processes and those that are higher-order develop over different time courses. These later developing aspects of vision are those that require the integration of information over space (such as contour integration) or space-time (such as global motion or pattern motion discrimination), and likely depend at least in part on the maturation of extrastriate visual areas. Moreover, these developmental programs can be modified by visual experience, with the later developing functions showing greater vulnerability to abnormal visual experience. This talk will describe the development of global form and motion perception, highlight the influence of abnormal visual experience and discuss underlying neural correlates.
Removing the brakes on brain plasticity in adults with amblyopia
Speaker: Dennis Levi, University of California, Berkeley
Experience-dependent plasticity is closely linked with the development of sensory function. Beyond this sensitive period, developmental plasticity is actively limited; however, new studies provide growing evidence for plasticity in the adult visual system. The amblyopic visual system is an excellent model for examining the “brakes” that limit recovery of function beyond the critical period. While amblyopia can often be reversed when treated early, conventional treatment is generally not undertaken in older children and adults. However new clinical and experimental studies in both animals and humans provide evidence for neural plasticity beyond the critical period. The results suggest that perceptual learning and video game play may be effective in improving a range of visual performance measures and importantly the improvements may transfer to better visual acuity and stereopsis. These findings, along with the results of new clinical trials, suggest that it might be time to re-consider our notions about neural plasticity in amblyopia.
Assessing visual functions in children with cortical visual impairment
Speaker: Gunilla Haegerstrom-Portnoy, University of California, Berkeley
CVI (cortical or cerebral visual impairment) refers to bilateral reduction in vision function due to damage to the visual cortex and/or the posterior visual pathways in the absence of ocular pathology. CVI is the most common cause of bilateral severe visual impairment in children in the developed world. The causes include hypoxic–ischemic brain damage, head injury (such as shaken baby syndrome), infection, hydrocephalus and metabolic disorders. CVI occurs commonly in premature infants and is often accompanied by cerebral palsy, quadraplegia, seizure disorders and developmental delay. Assessment of vision function in children with CVI is a challenge. Preferential looking methods and sweep VEP methods can be used sucessfully and in our population of children with CVI show an enormous range of values of visual acuity (20/50 to 20/800 VEP grating acuity) and contrast sensitivity (1.3 to 25% Michelsen contrast). Large discrepancies often occur between behavioral and VEP measures of function (often a factor of 10 or more). Longitudinal follow-up of 39 children with CVI over 6.5 years on average demonstrated significant improvement in about 50% of the patients and showed that early VEP measures can predict later behavioral vision function. Improvement in vision function occurred over a surprisingly long time (into the teens).