  The effects of temperature on various aspects of neural activity from single
cell to neural circuit level have long been known. However, how temperature
affects the system-level of activity typical of experiments using non-invasive
imaging techniques, such as magnetic brain imaging of electroencephalography,
where neither its direct measurement nor its manipulation are possible, is
essentially unknown. Starting from its basic physical definition, we discuss
possible ways in which temperature may be used both as a parameter controlling
the evolution of other variables through which brain activity is observed, and
as a collective variable describing brain activity. These two aspects are
further illustrated in the case of learning-related brain activity. Finally,
methods to extract a temperature from experimental data are reviewed.
