Functional MRI Limitations and Aspirations

Abstract

PrefaceThe idea of the present book emerged on the island of Elba in the summer of 2006 during an enjoyable and very fruitful workshop on thinking with the participation of most of the contributors of the present volume.The main intention behind the book is to address thinking by surveying the contribution of various functional neuroimaging methods to our understanding of the neural underpinnings of thinking. The major focus is on the methods applicable to the neurobiological study of human thinking, since much of what we consider complex thinking has to be considered as a part of the distinctive features of human nature.Despite the fact that we are far from a full understanding of the modularity of the human brain, the use of functional imaging techniques is obviously based on the premise that brain functions are modular.We are grateful to the distinguished authors, coming from different backgrounds, for their commitment to this project, which represents a true interdisciplinary approach, as is mandatory for this fascinating and challenging topic. We are also proud to have been able to recruit an outstanding worldwide team of contributors.We also wish to thank Anette Lindqvist and Dieter Czechlik from Springer Science+Business Media for their enthusiasm and constant support. Without their optimism and tireless efforts this volume would not have been possible. Munich, GermanyEduard Abstract Most would agree that knowing precisely what was happening in the brain during the act of thinking would help in our pursuit to understand what thinking really is. This chapter describes the basics, limits, and future directions of one of the more effective tools we have to observe the human brain while it is functioningfunctional MRI. Functional MRI emerged in the early 1990s, and has since grown explosively in utility. In this chapter, an in-depth exploration is carried out of what limits functional MRI to a spatial resolution of millimeters and a temporal resolution of seconds. In addition, issues of how sensitive functional MRI is in detecting brain activity and how deeply we can interpret the signal changes are explored. Lastly, the chapter ends with a discussion on how imaging might be essential, or perhaps irrelevant, to understanding thinking.

Widespread correlation patterns of fMRI signal across visual cortex reflect eccentricity organization

“…To compare the widespread eccentricity connectivity with other models of connectivity, each hemifield map was separated into six divisions of eccentricity, each containing six divisions of polar angle, yielding a total of 36 bins for each hemifield representation. Two spatial patterns of topographically local connectivity and two patterns of topographically widespread connectivity were generated: A. Topographically local connectivity: Instrumental ‘noise’ connectivity (NSE): subject-specific predicted ‘noise’ correlations that are assumed to be non-neuronal in nature, and could result from any biases introduced from data acquisition and analyses, as well as the intrinsic spatial signal spread in the BOLD imaging ( Bandettini, 2009 ). The point spread function at 3T has been estimated to be about 3.5 mm ( Engel et al, 1997 ).…”

Magnetic resonance imaging in Alzheimer’s disease and mild cognitive impairment

“…This is due to primary limitations including a low signal or contrast to noise ratio and the questionable validity of BOLD signal as a measure of neuronal activity. Unexplained variability in this signal might result from hemodynamic factors that are not controlled for [78]. …”

Physical principles for scalable neural recording

“…Although the existence of this paramagnetic reporter of oxygen metabolism is fortuitous, the data it provides is only an indirect readout of neural activity (Logothetis, 2008; Sirotin and Das, 2009; Jukovskaya et al, 2011), which is limited in its spatial and temporal resolution to the dynamics of blood flow in the brain's capillary network (1–2 s). The spatial point-spread function of the hemodynamic BOLD response is in the 1 mm range, although sub-millimeter measurements, revealing cortical laminar and columnar features, have been obtained by filtering out the signals from larger blood vessels (Bandettini, 2009). A significant area of current and future work is aimed at developing new molecular reporters that can be introduced into the brain to transduce aspects of neural signaling such as calcium spikes and neurotransmitter release into MRI- detectable magnetic or chemical signals (Shapiro et al, 2010; Hsieh and Jasanoff, 2012; Koretsky, 2012), as described in section 4.5.3, below.…”