Alyssa Brewer

By Alyssa A. Brewer and Brian Barton

Part of the book: Visual Cortex

By Alyssa Brewer and Brian Barton

Part of the book: Advanced Brain Neuroimaging Topics in Health and Disease

By Alyssa A. Brewer and Brian Barton

This chapter reviews the differences in specific structural and functional characteristics of human visual cortex among young adults, healthy aging adults, and patients with dementia, with a primary focus on those with Alzheimer’s disease (AD). Such visual cortex changes have been shown to underlie many of the behavioral deficits that develop in healthy aging and AD. Measurements of disordered visual cortex in dementia patients may be possible early in the course of neurodegeneration and thus may be useful for improving early diagnosis of these devastating diseases.

Part of the book: Update on Dementia

By Alyssa A. Brewer and Brian Barton

One of the fundamental properties of mammalian brains is that sensory regions of cortex are organized into multiple, functionally specialized cortical field maps (CFMs). An individual CFM is composed of two orthogonal topographical representations, reflecting two essential aspects of a sensory feature space. Each CFM is thought to subserve a specific computation or set of computations that underlie particular perceptual behaviors by enabling the comparison and combination of the information carried by the various specialized neuronal populations within this cortical region. Multiple adjacent CFMs, in turn, have now been shown by multiple laboratories to be organized in visual and auditory cortex into a macrostructural pattern called the cloverleaf cluster. CFMs within cloverleaf clusters tend to share properties such as receptive field distribution, cortical magnification, and processing specialization. This chapter will review the evidence for CFM and cloverleaf cluster organization across human visual and auditory cortex and will discuss the utility of these measurements for determining cortical structure and function and for investigating what changes occur in sensory cortex following various types of trauma or disease.

Part of the book: Sensory Nervous System

By Brian Barton and Alyssa A. Brewer

Human sensory systems are organized into processing hierarchies within cortex, such that incoming sensory information is analyzed and compiled into our vivid sensory experiences. Computations that are common to these sensory systems include the abilities to maintain enhanced focus on particular aspects of incoming sensory information (i.e., attention) and to retain sensory information in a short-term memory store after such sensory information is no longer available (i.e., working memory). In at least the auditory and visual systems, the necessary computational steps to create these experiences take place in cloverleaf clusters of cortical field maps (CFMs). The human auditory CFMs represent the spectral (i.e., tones) and temporal (i.e., period) aspects of sound, which are represented along the cortical surface as two orderly gradients that are physically orthogonal to one another: tonotopy and periodotopy, respectively. Knowledge of the properties of such CFMs is the foundation for understanding the specific sensory computations carried out in particular cortical regions. This chapter reviews current research into auditory nonverbal attention, auditory working memory, and auditory CFMs, and introduces the next steps to measure the effects of attention and working memory across the known auditory CFMs in human cortex using functional MRI.

Part of the book: The Human Auditory System