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This chapter describes a project completed during an industrial internship at
Blackrock Microimplantible Systems. The project consisted Oftesting and debugging a
system for concurrent microstimulation and recording, which at the time was called the
Stim Project. The system was designed to be connected to the Cerebus system, which is
Blackrock's 128 channel data acquisition system. The Cerebus system consists of a
Neural Signal Processing (NSP) unit, and a Neural Signal Amplifier (NSA) that has four
banks of 32-channel inputs. The NSA receives the analog signals from the
microelectrode(s) and amplifies them as well as providing some analog filtering before
passing them onto the NSP. The NSP converts the signals into digital form, and Can
perform a number of processing functions on the data (such as spike counting, spike
sorting, adjustable digital filtering, etc.) before passing the data to a computer for
viewing by the user. A single Stim Project unit was intended to allow concurrent
stimulation and recording on 32 channels, and would plug into one bank of the NSA.
The system was designed to be controlled through a serial port. The same computer
could be used to both receive data from the Cerebus system and control the Stim
Project.
Before the Stim Project could be a viable product, several challenges inherent to
simultaneous stimulation and recording had to be addressed. First the system must be
sensitive enough to be able to record the action potential of a single neuron with a high
level of resolution, yet be fairly immune to cross-talk and outside electromagnetic
interference that would drown out or obscure the signal. Secondly during stimulation
currents that are orders of magnitude larger than neural signals are used. These signals