  The curtain of technical limitations impeding rat multichannel non-invasive
electroencephalography (EEG) has risen. Given the importance of this
preclinical model, development and validation of EEG source imaging (ESI) is
essential. We investigate the validity of well-known human ESI methodologies in
rats which individual tissue geometries have been approximated by those
extracted from an MRI template, leading also to imprecision in electrode
localizations. With the half and fifth sensitivity volumes we determine both
the theoretical minimum electrode separation for non-redundant scalp EEG
measurements and the electrode sensitivity resolution, which vary over the
scalp because of the head geometry. According to our results, electrodes should
be at least ~3-3.5 mm apart for an optimal configuration. The sensitivity
resolution is generally worse for electrodes at the boundaries of the scalp
measured region, though, by analogy with human montages, concentrates the
sensitivity enough to localize sources. Cram\'er-Rao lower bounds of source
localization errors indicate it is theoretically possible to achieve ESI
accuracy at the level of anatomical structures, such as the stimulus-specific
somatosensory areas, using the template. More validation for this approximation
is provided through the comparison between the template and the individual lead
field matrices, for several rats. Finally, using well-accepted inverse methods,
we demonstrate that somatosensory ESI is not only expected but also allows
exploring unknown phenomena related to global sensory integration. Inheriting
the advantages and pitfalls of human ESI, rat ESI will boost the understanding
of brain pathophysiological mechanisms and the evaluation of ESI methodologies,
new pharmacological treatments and ESI-based biomarkers.
