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No single center within the nervous
system controls body temperature.
Rather, thermoregulation is a
process that involves a continuum
of neural structures and connections
extending from thehypothalamus
and limbic system through the
lower brainstem and reticular formation
to the spinal cord and sympathetic
ganglia (Figure 1).16 Nevertheless,
an area of the brain located
in and near therostral hypothalamus
seems to have a pivotal role in
the process of thermoregulation. Although
generally referred to as the
preoptic region, it actually includes
the medial and lateral aspectsof the
preoptic area, anterior hypothalamus,
and septum. Numerous studies
extending more than 60 years
have established that neurons located
in this region are thermosensitive
and exert at leastpartial control
over physiologic and behavioral
thermoregulatory responses.14,17
Many, although not all, thermophysiologists
believe that the
temperature-sensitive preoptic region
“regulates”body temperature
by integrating thermal input signals
from thermosensors in the skin
and core areas (including the central
nervous system).18 One of the
more widely held theories is that
suchintegration involves a designated
thermal set point for the preoptic
region that is maintained via
a system of negative feedback. According
to this theory, if the preoptic
temperature rises above itsset
point for whatever reason (eg, during
exercise), heat loss responses are
activated to lower body temperature
and return the temperature of
the preoptic region to the thermal set
point (eg,37.0°C).19 The thermal set
point of a particular heat loss response
is thus the maximum temperature
tolerated by the preoptic region
before the response is evoked.
If, on the other hand, thepreoptic
temperature falls below its thermal
set point (eg, as a result of cold exposure),
various heat retention and
heat production responses are activated
to raise body temperature and
with it...