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Introduction
Researchers have used both cortical recording and stimulation for decades in
order to investigate brain anatomy and physiology. Researchers will often record from
areas of interest while delivering stimuli (Hubei and Wiesel 1962), or having the subject
perform a task (Georgopoulos, et al. 1986), so that they can understand how neurons or
brain areas process information. Stimulating brain areas provides a uniquely direct way
to understand the functionality of a brain area, as stimulating a specific area can often
produce a behavior (Milad, et al. 2004) or percept (Murphey, et al. 2008) in the subject.
Additionally even stronger stimulation can be used to disrupt processing in an area
(Murasugi, et al. 1993) so that the importance of that brain area for a specific function
can be evaluated.
It would be highly desirable to be able to record and stimulate at the same time;
for example recording in surrounding tissue while stimulating would allow a researcher
to quantify the extent of cortical area that the stimulation is affecting. Likewise, by
stimulation in one area while recording in a distal région connectivity could be
established if resulting activity were recorded, and the number of intermediate
connections could be deduced from the latency. Unfortunately there are considerable
engineering challenges to overcome in order to be able to record while stimulating; this
is largely because while neuron potentials are on the scale of microvolts, stimulation
generally has to be on the order of millivolts or even volts in order to get an appreciable
effect.