Imaging the Brain with Optical Methods. Anna W. Roe, Ed. Springer 2010, pages 259, 115 illustrations, $189.00.
The book Imaging the Brain with Optical Methods edited by Dr. Anna W. Roe is a timely follow-up to previous volumes on similar topics (Optical Imaging of Brain Function and Metabolism 1 and 2 by U. Dirnagl et al., 1991 and 1997, and In Vivo Optical Imaging of Brain Function by Ron Frostig, 2002). Imaging the Brain with Optical Methods provides eleven chapters including an introductory chapter on the history of brain imaging by Dr. John S. George. The strength and novelty of this book are and chapters that elegantly demonstrate the utility of intrinsic optical signal imaging for studying complex functional properties and organization of brain cortex ranging from tactical stimulation to working memory. Three additional chapters provide discussion of fluorescence imaging and light scattering for monitoring changes of membrane potential and electrical activity in the brain. The final chapter discusses methods for monitoring activity-induced changes in blood velocity using two-photon laser scanning microscopy. The chapters are all well written by established investigators in the field and provide sufficient primary data, methodological details, and critical discussion of the strengths and weaknesses the methods utilized.
The introductory chapter does a good job of describing the necessity for investigating functional properties, especially electrophysiological responses, of neurons in large populations. Dr. George emphasizes that while a goal is spatial monitoring of electrical activity in brain, direct electrical measurements are hampered by poor resolution while indirect measurements such as functional MRI have temporal resolution typically orders of magnitude slower than electrical changes. He points out that optical measurements, either of intrinsic optical signals or of signals derived from dyes, can provide sufficient temporal and spatial resolution required for functional imaging. This chapter does a good job of introducing optical methods for monitoring changes in membrane potential and ions with fluorescent dye, intrinsic vascular changes associated with neuronal activity and intrinsic membrane changes monitored as changes in birefringence or light scattering. The introductory discussion of intrinsic optical signals associated with vascular reactivity to neuronal excitation was not extensively developed considering that many of the later chapters focused on this method. However, this may have been by design because the method was described in considerable detail in the subsequent chapters.
I found the strength of the book to lie in Chapters 3-8 which described data obtained under a variety of conditions in intact brain from rodents to humans using intrinsic optical signals. Yu et al., in Chapter 3 provide an excellent discussion of the origins of the intrinsic optical signals derived from vascular responses to neuronal excitation and provide interesting data concerning the role of astrocytes as mediators of this response. In Chapter 4, Chen et al., describe elegant experiments using intrinsic optical imaging to study somatosensory cortex function in anesthetized monkeys. In Chapter 5, Tanifuji et al., show how optical imaging in the cortex could be used to study the spatial representation of visual objects in the inferotemporal cortex of macaques. Dr. Roe, in Chapter 6, describes innovative studies using intrinsic optical signals to study working memory in cortex of rhesus monkeys. Chapter 7, written by Hongtau et al., describes how intrinsic optical signals could be monitored in human cortex during surgical procedures and how these signals might be used to investigate human neurological disease such as epilepsy. Finally, Hespos et al., in Chapter 8 describe the use of near-infrared optical imaging through the intact skull of human infants.
Chapter 9, by Roland et al., describes the utility of using voltage sensitive fluorescent dyes to spatially monitor electrical activity in cortex. This chapter provides a good discussion of the relative advantages (increased spatial and temporal resolution), and disadvantages (interference by vascular changes, changes in dye signal over time) of dyes compared to intrinsic optical signals. The chapter presents very interesting data using voltage sensitive dyes to monitor rapid spatial changes in cortical function following somatosensory or visual excitation of rodent cortex.
The remaining chapters, Chapter 2, 10 and 11, describe methods that are currently either in development or have been used less extensively for imaging brain activity in vivo. Chapter 2, by Jin et al., describes the use of genetically encoded sensors of membrane potential. For this approach, voltage-sensitive fluorescent proteins are expressed selectively in certain brain cell types, which would allow imaging of changes in membrane potential. The approach is well described for cells in vitro but has not yet been attempted in vivo. In Chapter 10, Schei and Rector describe the use of optical changes in light scattering to detect fast functional responses of neurons. Some interesting imaging data is shown from rodent somatosensory cortex to validate the utility of the approach. Finally, Devor et al., in Chapter 11 describe the use of two photon laser scanning microscopy as a method to study dynamic changes in the cortical vasculature associated with alterations in cortical function. While not a procedure for functional imaging, this method should be useful for better understanding the mechanisms associated with changes in vascular reactivity that underlie intrinsic optical signals.
In summary, this is a timely book on optical imaging that focuses on the use of these approaches to study spatial activation patterns in brain. The book is generally well written with extensive use of impressive color figures for display of brain activity patterns. All of the chapters provide critical reviews of both the advantages and disadvantages of the methods. By necessity, the Chapters are technical in nature and, thus, would be most easily read by experienced investigators in this field.
