Biomedical Engineering Reference
In-Depth Information
Chapter 10
Tactile and Non-tactile Sensory Paradigms for fMRI
and Neurophysiologic Studies in Rodents
Basavaraju G. Sanganahalli, Christopher J. Bailey, Peter Herman,
and Fahmeed Hyder
Abstract
Functional magnetic resonance imaging (fMRI) has become a popular functional imaging tool for human
studies. Future diagnostic use of fMRI depends, however, on a suitable neurophysiologic interpretation
of the blood oxygenation level dependent (BOLD) signal change. This particular goal is best achieved
in animal models primarily due to the invasive nature of other methods used and/or pharmacological
agents applied to probe different nuances of neuronal (and glial) activity coupled to the BOLD signal
change. In the last decade, we have directed our efforts towards the development of stimulation proto-
cols for a variety of modalities in rodents with fMRI. Cortical perception of the natural world relies on
the formation of multi-dimensional representation of stimuli impinging on the different sensory systems,
leading to the hypothesis that a sensory stimulus may have very different neurophysiologic outcome(s)
when paired with a near simultaneous event in another modality. Before approaching this level of com-
plexity, reliable measures must be obtained of the relatively small changes in the BOLD signal and other
neurophysiologic markers (electrical activity, blood flow) induced by different peripheral stimuli. Here we
describe different tactile (i.e., forepaw, whisker) and non-tactile (i.e., olfactory, visual) sensory paradigms
applied to the anesthetized rat. The main focus is on development and validation of methods for repro-
ducible stimulation of each sensory modality applied independently or in conjunction with one another,
both inside and outside the magnet. We discuss similarities and/or differences across the sensory systems
as well as advantages they may have for studying essential neuroscientific questions. We envisage that the
different sensory paradigms described here may be applied directly to studies of multi-sensory interac-
tions in anesthetized rats, en route to a rudimentary understanding of the awake functioning brain where
various sensory cues presumably interrelate.
Key words:
Blood volume, glucose, glutamate, metabolism, neurovascular coupling, oxygen.
1. Introduction
Dynamic imaging of human brain function began approximately
two decades ago with positron emission tomography (PET) (for
