Large extracellular spikes recordable from axons in microtunnels

Area of Science:

• Neuroscience
• Biophysics
• Bioengineering

Background:

• Extracellular action potentials (spikes) from cultured neurons typically have small amplitudes when recorded in open wells.
• This is despite originating from large surface areas of neural cell somata, often falling below the noise level.

Purpose of the Study:

• To investigate methods for enhancing the amplitude and signal-to-noise ratio of extracellularly recorded neuronal spikes.
• To explore the effect of confined microenvironments on action potential signal characteristics.

Main Methods:

• Rat cortical neurons were cultured in a two-well system separated by microtunnels (3 × 10 μm).
• Neurons formed feed-forward networks between assemblies in different wells.
• Extracellular spikes were recorded from axons within microtunnels and compared to those in open wells.

Main Results:

• Spikes recorded within microtunnels showed amplitudes several orders of magnitude larger than in open wells.
• High signal-to-noise ratios (up to 450) were achieved, with average amplitudes exceeding 250 μV and some reaching 4.5 mV.
• Signal amplitude demonstrated a dependence on microtunnel impedance.

Conclusions:

• Restricted volumes within microtunnels significantly enhance extracellularly recorded neuronal spike amplitudes.
• This microtunnel-based recording approach offers a substantial improvement over traditional open well methods for neural signal detection.
• The findings suggest microtunnels are a promising tool for high-fidelity neural recordings.