  Numerous measurements in the brain of the impedance between two extracellular
electrodes have shown that it is approximately resistive in the range of
biological interest, $<10\,$kHz, and has a value close to that expected from
the conductivity of physiological saline and the extracellular volume fraction
in brain tissue. Recent work from the group of Claude B\'edard and Alain
Destexhe has claimed that the impedance of the extracellular space is some
three orders of magnitude greater than these values and also displays a
$1/\sqrt{f}$ frequency dependence (above a low-frequency corner frequency).
Their measurements were performed between an intracellular electrode and an
extracellular electrode. It is argued that they incorrectly extracted the
extracellular impedance because of an inaccurate representation of the large,
confounding impedance of the neuronal membrane. In conclusion, no compelling
evidence has been provided to undermine the well established and physically
plausible consensus that the brain extracellular impedance is low and
approximately resistive
