Biomedical Engineering Reference
In-Depth Information
FIgURE 7.4:
Implantation of the flexible substrate microwire array.
Extracellular potentials recorded at 12 207 Hz during surgery were analyzed and spike sorted
using Spike2 (CED, Cambridge, UK) software package. Recordings were analyzed over a period of
130 sec. To detect and sort neural activity within each channel, an automated waveform matching
system within Spike2 was used to construct templates using threshold detection.
Once a set of waveform templates were generated for a data stream, all templates (noise) that
did not match characteristic neural depolarization behavior were removed [
46-48
]. The remaining
waveform templates were sorted according to amplitude and shape, and any waveform templates
that were significantly similar to each other were combined into a single template. Clustering of
waveform variance within templates was verified through PCA. Each waveform template was sta-
tistically unique and representative of a distinct neuron within the channel.
Once neuron waveforms were isolated and sorted, peak-to-peak amplitude was evaluated
by computing the average waveform of all spikes within the neuron template and measuring the
potential difference from the apex of the repolarization peak to the apex of the depolarization peak.
The noise floor of each channel was evaluated by computing the root mean square value of a 5-sec
period of noise. Using these two values, the SNR for each neuron template was calculated. To ensure
proper reporting, all spike waveform templates that possessed peak-to-peak amplitude of magnitude
less than three times the value of the noise floor were considered too close to the noise to be reliably
and consistently distinguished, and were removed from the study. Values of neural yield, noise floor,
amplitude, and SNR are reported for each channel within Table
7.1
. Action potential amplitudes as
