1 THE AUTONOMIC PHYSIOLOGY OF TERROR MANAGEMENT ...

on the heart fast enough to affect changes that dramatically from beat to beat, the
percentage of such changes in any given series is taken to index the strength of vagal
control on the heart. Correlations with standard RSA measures are generally quite high
(e.g., greater than .85, Allen, 2002). The pNN50 is particularly appealing because it is
simple to compute and interpret, and is more resistant to outlier data than other indices
such as RSA (Burr et al., 2003).
Vagal Tone Connections to Psychological Threat
This innovation in measuring parasympathetic influence has led to a surge in
vagal tone related work in humans that tends to support the threat-buffering perspective
of parasympathetic nervous system functioning at the heart. Contributing to a shift in
focus away from the sympathetic system that for most of the century dominated the field,
this body of data generally focuses on vagal tone as a predictor of anxiety, hostility, and
depression. In addition, a body of work also investigates vagal tone in conjunction with
more cognitive and attentional processes.
Below we will review much of this work. The review, however, will be limited to
work in adults. Infant and child data will not be brought to bear on theorizing about vagal
tone in adults for two main reasons. First, the vagus nerve controls the heart substantially
less in infancy than afterwards (e.g., Porges, Doussard-Roosevelt, Portales, & Suess,
1994; Izard, Porges, Simons, Haynes, & Cohen, 1991). This makes vagal tone in infants
and adults difficult to compare. For instance, high vagal tone in infants would be
considered low vagal tone if compared with adults. A second reason to avoid drawing
conclusions about vagal tone in adults from vagal tone correlates in infancy is that vagal
28