Phase 4 · Electrophysiology Core & Instrumentation Visit

Lab Visit: High-Density EEG & Electrophysiology Core

Experimental protocols for 128/256-channel high-density electroencephalography, Faraday cage isolation, electrode impedance physics, active shielding, and continuous neonatal amplitude-integrated EEG (aEEG).

Course: IDNE 701 (Fall 2026) Date: Nov 06, 2026 (Week 11) Location: Neuroengineering Electrophysiology Core Instructor: Mark Bolding, PhD

01. Instrumentation & Shielding Infrastructure

The Neuroengineering EEG Core facility features double-walled Faradaic copper-mesh shielded testing suites designed to attenuate ambient AC powerline induction ($60\,\text{Hz}$) by $> 80\,\text{dB}$.

🛡️ Active Shielding & Driven Right Leg (DRL)

Cable capacitance introduces $60\,\text{Hz}$ displacement currents. Active coaxial shielding drives outer cable shields at the common-mode voltage, eliminating dielectric leakage currents. DRL circuits invert common-mode noise and drive it back to the body, boosting CMRR to $> 110\,\text{dB}$.

⚡ High-Density Montages (128 / 256 Channels)

Geodesic sensor nets use $\text{Ag/AgCl}$ sintered pellets with sponge reservoirs soaked in potassium chloride electrolyte. Enables whole-head scalp potential mapping with inter-electrode distance $\le 15\,\text{mm}$.

02. Volume Conduction & The Forward Lead-Field Matrix

Scalp surface potentials $V_e$ represent volume-conducted superposition of dipolar current sources $\vec{J}_p(\vec{r})$ across cortical pyramidal columns:

$$\nabla \cdot (\sigma(\vec{r}) \nabla \Phi(\vec{r})) = \nabla \cdot \vec{J}_p(\vec{r}) \implies \mathbf{v} = \mathbf{L}\mathbf{j} + \mathbf{n}$$

Equation 1: Quasi-static Poisson volume conduction and discrete lead-field matrix L

Because skull conductivity is $\approx 1/15$ to $1/80$ of brain tissue, the adult skull acts as a spatial low-pass filter, blurring high spatial frequency electric fields.

03. Grand Challenge Focus: Neonatal Amplitude-Integrated EEG (aEEG)

📉 Asymmetric Compression & Filtering

Raw single- or dual-channel EEG (C3–P3, C4–P4) is bandpass filtered ($2 - 15\,\text{Hz}$), rectified, and logarithmically compressed below $10\,\mu\text{V}$. The signal is displayed at a slow time scale ($6\,\text{cm/hr}$), allowing neonatologists to visually track sleep-wake cycling and burst-suppression trends over 72 hours at a glance.

🧠 Thin Fontanelle Conductivity Contrast

The neonatal cranium is thin ($1.5\,\text{mm}$) and fontanelles have the high electrical conductivity of CSF ($\sigma \approx 1.79\,\text{S/m}$), with no insulating bone. Consequently, neonatal scalp potentials exhibit much higher amplitude and higher spatial gradient sharpness than adult EEG.