Mapping Human Visual and Auditory Cortex, Tracking Plasticity, and Linking fMRI to Perception

Volume 1: The current understanding of the organization of the human visual system is discussed, with emphasis on the travelling wave and population receptive field (pRF) modeling methods of measuring visual field maps (VFMs) in humans. Functional magnetic resonance imaging (fMRI) measurement of pRFs of neurons in the visual cortices of humans revealed VFMs organized into roughly circular `clover leaf' clusters. These VFMs were compared between normal, aging, and diseased brains to understand how the brain changes over time and help develop tools to differentiate normal aging and dementia. Finally, visual working memory, the ability to hold things in mind for brief periods of time, and its likely relationship to VFMs is discussed, with implications for future research.;Volume 2: Plasticity, the brain's ability to change itself, is discussed in the context of normal and abnormal development in individuals with rod monochromatism, achiasmia, and a missing right hemisphere, with an emphasis on human fMRI measurement methodology. The rod scotoma lacks rod photoreceptors and thus visual input under low-light conditions, yet subjects report perception in the scotoma to varying degrees across stimuli, which we linked to cortical fMRI measurements in VFMs. Plasticity was measured for visuo-motor transformations by left-right reversing the visual field for normal subjects for extended periods and using fMRI to track changes in their VFMs in posterior parietal cortex. Short-term adaptation to left-right visual field reversal was compared between two polymorphisms of brain-derived neurotrophic factor (BDNF), revealing that subjects with resulting higher plasticity took longer to adapt than their counterparts.;Volume 3: The current understanding of the organization of the human auditory system with respect to the tonotopic (frequency) mapping of the cochlea is discussed, with emphasis on the challenges of localizing auditory maps with only one sound dimension. A modified version of the travelling wave method was used to investigate auditory cortex with fMRI, providing the first evidence in humans for two-dimensional auditory field maps (AFMs) consisting of orthogonal tonotopic (frequency) and periodotopic (temporal) gradients. Finally, cross-sensory activation in human primary visual and auditory cortex was measured using the modified travelling wave and pRF modeling fMRI methods.