The relationship between BOLD signal and autonomic nervous system functions: Implications for processing of "physiological noise".
Abstract:
Functional magnetic resonance imaging (fMRI) research has
revealed not only important aspects of the neural basis of
cognitive and perceptual functions, but also important
information on the relation between high-level brain
functions and physiology. One of the central outstanding
questions, given the features of the Blood Oxygenation
Level-Dependent (BOLD) signal, is whether and how autonomic
nervous system (ANS) functions are related to changes in
brain states as measured in the human brain. A
straightforward way to address this question has been to
acquire external measurements of ANS activity such as
cardiac and respiratory data, and examine their relation to
the BOLD signal. In this work we describe two conceptual
approaches to the treatment of ANS measures in the context
of BOLD fMRI analysis. On the one hand, several research
lines have treated ANS activity measures as noise,
considering them as nothing but a confounding factor that
reduces the power of fMRI analysis or its validity. Work in
this line has developed powerful methods to remove ANS
effects from the BOLD signal. On the other hand, a different
line of work has made important progress in showing that ANS
functions such as cardiac pulsation, heart rate variability
and breathing rate, could be considered as a theoretically
meaningful component of the signal that is useful for
understanding brain function. Work within this latter
framework suggests that caution should be exercised when
employing procedures to remove correlations between BOLD
data and physiological measures. We discuss these two
positions and the reasoning underlying them. Following, we
draw on the reviewed literature in presenting practical
guidelines for treatment of ANS data, which are based on the
premise that ANS data should be considered as theoretically
meaningful information. This holds particularly when
studying cortical systems involved in regulation, monitoring
and/or generation of ANS activity, such as those involved in
decision making, conflict resolution and the experience of
emotion.