Figure 1.
Comb-like, silicon-based NeuroProbes array with four 10-mm-long probe shafts separated by 400 µm.
Each shank is comprised of eight IrOx electrode sites. The array is interconnected to a highly flexible polyimide ribbon cable interfacing with a zero insertion force (ZIF) connector on a printed circuit board (PCB) that was connected to the stimulator. For probe insertion, the probe comb is fixed adhesively to the insertion plate and attached to a micromanipulator. The 100-µm-thick probe shanks proved to be stiff enough for insertion into deep brain structures.
Figure 2.
A) Averaged unfiltered raw data (20 sweeps) showing LFP in response to stimulation with an NP site from 20 to 52 dB relative to 1 µA (actual stimuli were 12–52 dB in 2-dB steps). The monotonic increase in LFP size with stimulation amplitude is evident. The LFP threshold is 28 dB in this example. B) PSTHs corresponding to the different stimulation levels indicated in each plot. PSTH bars represent 1 ms bins. The dotted line indicates stimulus onset at 0 ms. Bottom right trace is a single trial filtered for spikes with the artifact removed and showing multi-unit activity in response to a stimulation at 52 dB. Each detected spike is marked by an * with the red line indicating threshold for spike detection. The MUA threshold is 34 dB, which is higher than the LFP threshold.
Figure 3.
Rate growth curves recorded from A1 and pooled from all 12 stimulated NP sites.
A) Growth rate of LFP peak magnitude versus stimulus level (in dB relative to 1 µA). B) Growth rate of LFP area versus stimulus level. C) Growth rate for multi-unit spikes versus stimulus level.
Figure 4.
Modeled safe stimulation parameters.
Stimulation above the solid black line (k = 2) has been shown to induce tissue damage and co-varies with total charge and charge density per pulse phase. The curves with different symbols reflect how charge density changes with increasing charge per phase for either the NP or AMI sites, i.e., for different site areas, for three different pulse widths each. The local field potential (LFP, red dot, 200 µs/phase) and spike (Spk, blue dot, 200 µs/phase) thresholds obtained from animal studies are labeled on the plot for direct comparison.