Biomedical Engineering Reference
In-Depth Information
FIgURE 7.:
Block diagram for the PICO wireless neural recording system.
provides a block diagram for signal flow throughout the system. The Pico Remote senses single- and
multiunit neuronal activity from 16 chronically implanted microelectrodes from a laboratory rat. The
signals are amplified (80 dB) with a custom amplifier1 and fed to one of eight 12-bit A/D channels2
sampling at 20 kHz on the MSP430. The MSP430 has two modes: spike sorting and spike reading.
While in the spike sorting mode, raw sampled data from a single probe are sent over the Nordic trans-
ceiver for reception by the Pico Receiver. This mode allows the user to analyze in detail the raw re-
cording from the microelectrodes to set thresholds for detecting and sorting spikes (action potentials).
In the spike reading mode, the MSP430 executes the spike detection through user defined thresholds
and sorting. The firing rate for each neuron is computed locally and sent over the Nordic transceiver
for reception by the Pico Receiver.
The Nordic transceiver is capable of up to 250 kbit/sec sustained data transfer of packet data.
Data sent over the Nordic transceivers are fed to another MSP430 processor for buffering and for-
matting and for the eventual pass through to a Silicon Laboratories CP2103 USB bridge to software
running on a PC.
The MSP430F1611 processor samples each analog channel at 20 kHz with an on-board
12-bit A/D converter. Depending on the mode in which the processor is functioning, the samples
are handled differently. While in the spike sorting mode, no signal processing occurs and the raw
samples are sent directly to the transceiver for processing by software running on the PC. The data
are sent as 12-bit samples at rate of 20k samples/sec for a data rate of 240k samples/sec. In the
spike counting mode, each sample is compared against thresholds that define a spike using well
