HD Series Silicon Probes (High-Density)

Overview

The HD (High-Density) Series represents NeuroNexus' ultra-high-density silicon probe line, featuring recording sites spaced at 10-20 µm intervals - significantly closer than standard probes (50-100 µm). This dense site packing enables exceptionally high spatial resolution for cortical layer mapping, single-unit discrimination, and current source density (CSD) analysis. HD probes are designed for applications where resolving fine-scale spatial structure of neural activity is paramount.

HD probes address a key limitation of traditional probes: spatial undersampling. With sites spaced at 50-100 µm, standard probes may miss neurons located between recording sites or fail to resolve laminar boundaries. HD probes mitigate this by providing near-continuous spatial sampling along the penetration axis, ensuring comprehensive coverage of neural populations and precise localization of layer-specific activity.

Design Philosophy

The HD Series prioritizes:

• Spatial Resolution: Near-continuous sampling along penetration axis (10-20 µm spacing)
• Laminar Profiling: Resolve cortical/hippocampal layer boundaries with high precision
• Single-Unit Isolation: Multiple sites per neuron improve spike sorting accuracy
• CSD Analysis: Dense sampling enables accurate current source density estimation

Key Specifications

Geometric Parameters

• Shank Configuration: Single linear shank (multi-shank HD variants available)
• Shank Length: 3mm, 5mm, 7mm, 10mm (standard lengths)
• Shank Width: 80-120 µm (varies by model)
• Shank Thickness: 15 µm (standard), 30 µm (chronic variants)
• Site Spacing:
  • Ultra-Dense: 10 µm (extreme resolution, neuropixels-like)
  • High-Dense: 15-20 µm (balance resolution and site count)
  • Standard-Dense: 25 µm (dense but manageable channel counts)

Electrical Characteristics

• Recording Sites: 64, 128, 256, 384 sites (high channel counts)
• Site Area: 100-177 µm² (smaller sites accommodate tight spacing)
• Impedance: 1.5-3.5 MΩ @ 1 kHz (higher due to smaller site area)
• Material: Iridium sites (preferred for low-noise spike detection)
• Conductor: Gold traces with high-density routing

Physical Properties

• Substrate: Silicon (15 µm standard, 30 µm chronic)
• Weight: 1-2 grams (including connector)
• Sterilization: EtO compatible
• Connector: High-density connectors (64-384 channels)

Recording Capabilities

Ultra-High Spatial Resolution

• Laminar Boundaries: Resolve cortical layers (L1, L2/3, L4, L5, L6) with <50 µm precision
• Hippocampal Layers: Distinguish CA1 pyramidal layer, stratum radiatum, oriens with high clarity
• Single-Unit Localization: Determine neuron depth within ±10 µm (multiple sites per neuron)
• Traveling Wave Detection: Resolve propagation velocities with high temporal-spatial precision

Signal Types

• Single-Unit Activity (SUA): Multiple sites per neuron improve cluster separation
• Multi-Unit Activity (MUA): High-resolution MUA gradients across layers
• Local Field Potentials (LFP): Layer-specific oscillations and CSD analysis
• Current Source Density (CSD): Identify synaptic current sinks/sources with high accuracy

Bandwidth

• Spike Band: 300 Hz - 10 kHz (high-frequency spikes)
• LFP Band: DC - 500 Hz (layer-specific oscillations)
• CSD Requirements: Requires dense spatial sampling (HD spacing essential)
• Sampling Rates: 30-40 kHz (high-channel-count systems)

Typical Applications

Cortical Laminar Studies

• Layer-Specific Activity: Dissect activity patterns across cortical layers (L2/3 vs. L5)
• Feedforward vs. Feedback: Distinguish layer 4 (FF) from layer 1 (FB) inputs
• Columnar Organization: Map functional columns with high spatial precision
• CSD Analysis: Identify synaptic inputs by layer (sink/source patterns)

Hippocampal High-Resolution Recording

• CA1 Pyramidal Layer: Precise localization within thin pyramidal cell layer (~50 µm)
• Dendritic Recording: Sample stratum radiatum and lacunosum-moleculare dendrites
• Sharp-Wave Ripples: High spatial resolution of ripple initiation and propagation
• Theta Phase: Resolve theta phase gradients across hippocampal layers

Single-Unit Sorting Advantages

• Multi-Site Waveforms: Same neuron detected on 4-8 adjacent sites (superior clustering)
• Unit Localization: Depth estimation within ±10 µm (amplitude decay across sites)
• Drift Compensation: Track units during probe drift (waveform shifts across sites)
• Overlapping Units: Separate neurons with similar waveforms but different depths

Species Compatibility

• Rodents: Mice (ideal due to thin brain structures), rats (excellent cortical coverage)
• Non-Human Primates: Cortical laminar studies (thicker cortex benefits from HD sampling)
• Other Mammals: Any application requiring high-resolution laminar profiling

High-Density Advantages

Why Ultra-Dense Spacing?

1. Avoid Spatial Aliasing: Nyquist principle - sample at 2× the spatial frequency of interest
2. CSD Accuracy: CSD requires dense sampling (second spatial derivative amplifies noise without dense sites)
3. Layer Boundary Detection: Cortical layers can be <100 µm thick (require <20 µm sampling)
4. Unit Triangulation: Multiple sites per neuron enable precise depth localization

HD vs. Standard Probes (A-Series, Vector)

• HD Series: 10-20 µm spacing, 128-384 sites, laminar precision
• Standard: 50-100 µm spacing, 16-64 sites, general-purpose
• Choose HD: Laminar analysis, CSD, high-resolution single-unit localization
• Choose Standard: General electrophysiology, cost-sensitive, established protocols

HD vs. Neuropixels

• Neuropixels: 10 µm spacing, 384 sites, 960 total (multiplexed), CMOS-integrated
• HD Series: 10-20 µm spacing, 64-384 sites (all active), silicon microfabricated
• Choose Neuropixels: Ultra-high-density, multi-region, commercial availability
• Choose HD Series: Custom geometries, specific brain regions, NeuroNexus ecosystem compatibility

Technology Details

Fabrication Precision

• Site Alignment: Sub-micron placement accuracy (critical for dense spacing)
• Trace Routing: Complex routing of 128-384 traces to connector
• Impedance Uniformity: Tight impedance tolerances across all sites (critical for CSD)

Manufacturing Heritage

• Michigan-Rochester Collaboration: Developed for high-resolution cortical studies
• CSD Optimization: Site spacing designed for accurate second-order spatial derivatives
• Chronic Variants: Thicker substrates available for long-term HD recording

Quality Control

• Site Spacing Verification: Optical measurement of inter-site spacing (<1 µm tolerance)
• Impedance Testing: All channels tested (identify high-impedance sites)
• Crosstalk Testing: Ensure no electrical coupling between adjacent dense sites

Comparison with Other Families

HD vs. A-Series

• HD: 10-20 µm spacing, 128-384 sites, high spatial resolution
• A-Series: 50-100 µm spacing, 16-64 sites, cost-effective
• Choose HD: Laminar profiling, CSD analysis, ultra-high-resolution
• Choose A-Series: General electrophysiology, budget constraints

HD vs. Q-Trode Series

• HD: Dense linear sampling, laminar emphasis
• Q-Trode: Tetrode configurations, spike sorting emphasis
• Choose HD: Laminar resolution, CSD, layer-specific dynamics
• Choose Q-Trode: Single-unit isolation from specific depths (not layer-continuous)

HD vs. Matrix Series

• HD: Single shank, ultra-dense vertical sampling
• Matrix: Multi-shank, broader spatial coverage but lower density per shank
• Choose HD: Single-penetration laminar profiling
• Choose Matrix: Multi-region volumetric recording

HD vs. Vector Series

• HD: Ultra-dense spacing, high channel counts
• Vector: Standard spacing, chronic-optimized substrate
• Choose HD: Spatial resolution priority (acute or short chronic)
• Choose Vector: Long-term chronic durability priority

Available Products

HD Series models emphasize dense site packing:

Popular Models

• HD1x128-5mm-15-100: 128 sites, 5mm shank, 15 µm spacing (ultra-dense)
• HD1x64-5mm-20-177: 64 sites, 5mm shank, 20 µm spacing (balance density and channels)
• HD1x256-10mm-10-100: 256 sites, 10mm shank, 10 µm spacing (extreme resolution)
• HD2x64-5mm-15-100: Dual-column 128 sites for broader lateral coverage

Naming Convention

• HD: HD Series family identifier
• 1x128: 1 column × 128 sites
• 5mm: Shank length
• 15: Site spacing (µm) - ultra-dense
• 100: Site area (µm²) - small sites

View all HD Series products in catalog →

Surgical Considerations

Implantation Best Practices

• Stereotaxic Precision: High-resolution targeting (HD data only useful if precise location known)
• Slow Insertion: 1-2 µm/s to minimize tissue displacement across dense sites
• Dura Removal: Complete dura removal (dense sites won't penetrate dura)
• Angle Control: Perpendicular insertion critical (angled insertion complicates layer assignment)

Acute Recording Protocol

• Depth Advancement: Step-wise advancement, monitor impedance changes (layer boundaries)
• Settling Time: 60-90 minutes (dense sites = more tissue contacts = longer stabilization)
• Reference Selection: Distant reference (cerebellar or contralateral cortex)

Chronic Implantation

• Challenge: High channel counts increase connector weight and complexity
• Substrate: Use 30 µm chronic variants if available
• Cementing: Robust multi-layer acrylic (heavier connectors require stronger anchoring)
• Unit Tracking: Dense sites enable tracking same neurons across days (amplitude ratios across sites)

Best Practices

Before Recording

• Impedance Mapping: Test all 128-384 channels (identify dead channels before surgery)
• Amplifier Compatibility: Ensure recording system supports high channel counts and sampling rates
• Data Storage: Plan for large data volumes (256 channels @ 30 kHz = 15.36 MB/s = 55 GB/hour)

During Recording

• Layer Assignment: Use LFP features to identify layers (e.g., theta phase reversal for CA1 pyramidal layer)
• CSD Calculation: Requires precise site spacing knowledge (verify in metadata)
• Reference Stability: Dense sites amplify reference noise (ensure low-noise reference)
• Data Management: Continuous recording generates massive datasets (have real-time compression or selective saving)

After Recording

• Spike Sorting: Use algorithms designed for dense arrays (template matching, KiloSort)
• CSD Analysis: Second spatial derivative (ΔV/Δz²) requires smoothing/filtering
• Layer Mapping: Align CSD sinks/sources to known anatomical layers via histology

Troubleshooting

Common Issues

• Excessive Data Volume: 256-384 channels generate terabytes per experiment (compression, selective channels)
• Reference Noise: Dense sites amplify poor reference (use differential reference or offline re-referencing)
• Dead Channels: High channel counts increase probability of defective sites (test before use)
• Spike Sorting Challenges: Dense sampling creates overlapping waveforms (use template matching algorithms)

Related Technologies

Packaging Options

• High-Density Connectors: 128-384 pin Omnetics connectors
• Active Amplification: On-board amplifiers reduce cable capacitance noise (critical for dense arrays)

Complementary Products

• High-Channel-Count Systems: Intan RHD Recording System, Open Ephys, Neuropixels-compatible systems
• CSD Analysis Software: MATLAB CSD Toolbox, Python MNE-Python
• Spike Sorting: KiloSort2/3, MountainSort, Spyking Circus (dense-array optimized)

Resources

Documentation

• HD Series Product Guide (PDF) - Specifications and site spacing details
• CSD Analysis with HD Probes - Current source density calculation guide
• High-Density Spike Sorting Guide - Best practices for dense array unit isolation

Application Notes

• AN-089: HD Probe Laminar Profiling in Neocortex
• AN-092: Current Source Density Analysis with HD Arrays
• AN-101: Single-Unit Localization Using Dense Sampling

Publications (Selected)

HD probes and dense arrays have enabled high-resolution systems neuroscience:

• Fernández-Ruiz et al. (2021). "Long-duration hippocampal sharp wave ripples" Neuron - HD laminar hippocampal recordings
• Senzai et al. (2019). "Layer-specific physiological features and interlaminar interactions" Neuron - HD cortical laminar analysis
• Jun et al. (2017). "Fully integrated silicon probes for high-density recording" Nature - Neuropixels (similar dense-array concept)

Support

• Technical Support: [email protected]
• CSD Analysis Consultation: [email protected]
• Sales Inquiries: [email protected]

---

Last Updated: March 1, 2026
Part of the NeuroNexus Product Family Documentation