Visual Plasticity After Brain Damage
Damage to the adult primary visual cortex (V1) causes a loss of conscious vision over the same part of the visual field in both eyes - termed partial cortical blindness. This increasingly common cause of permanent disability in older, adult humans is still considered untreatable. However, the existence of blindsight (a largely unconscious ability to sense moving and flickering stimuli) suggests partial preservation of visual processing in cortically blind fields. Blindsight is thought to be mediated by projections from the superior colliculus via the pulvinar, to hMT+ (the human MT complex, equivalent to macaque MT+MST) or from the dLGN directly to hMT+. The existence of visual pathways that bypass V1 begs the question: can they be recruited to restore vision in cortical blindness?
Our team recently discovered that visual training can recover normal threshold levels of discrimination and awareness for both simple and complex motion in the trained regions of cortically blind fields. However, the extent of recovery possible and the mechanisms underlying it are unknown.
Our long-term objective is to define a new paradigm for understanding visual recovery after permanent visual cortex damage. Specifically, we are interested in characterizing the properties of, and signal processing mechanisms that enable visual relearning and recovery in cortical blindness. This knowledge should allow us to predict the extent to which vision can be recovered, as well as the quality and modality of recovered vision that can be attained in a given individual.
Our laboratory uses a combination of tools and approaches to achieve our research goals, including psychophysics, functional MRI (fMRI), electroencephalography (EEG), and virtual reality. Ongoing projects include:
- Assessing visual discrimination abilities that can be retrained in cortically blind fields and measuring their specificity
- Characterizing the signal processing mechanisms underlying relearning in cortically blind fields
- Using fMRI, study the pattern of visually-evoked signals in spared early and higher-level visual areas and assess how they are altered by visual training that recovers vision
- Understanding how cortically blind subjects use visual information from blind and sighted regions of their visual field in order to navigate.
Our results are intended to provide critical information about brain pathways and signal processing mechanisms stimulated by training to evoke visual relearning after permanent visual cortex damage in adulthood. This knowledge is essential theoretically to better understand the type and degree of plasticity possible in damaged, adult visual systems, as well as to improve our treatment strategies for humans suffering from disability induced by such permanent damage.