Neural Noise

Optimal interphase delay in biphasic pulses for microstimulation in mouse visual cortex

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  • Optimal interphase delay in biphasic current pulses facilitates neural circuit activation induced by microstimulation in the mouse visual cortex 1.
  • The finding informs safer, more effective cortical and sensory stimulation for neural interfaces and neuroprosthetics 1. 1

Weekly enrichment (2026-07-20)

  • The study was published in Frontiers in Neuroscience (2025, article 1710221) and used voltage-sensitive dye imaging in mouse brain slices to directly visualize membrane excitation from cathodic-first biphasic current pulses with varying interphase delays.23
  • At a stimulation intensity of 10 µA/phase with 200 µs/phase, an interphase delay of 500-600 µs produced larger cortical circuit excitation than shorter delays, longer delays, or a cathodic monophasic pulse — a nonlinear (not merely additive) facilitation.23
  • At a higher intensity of 20 µA/phase, the pattern shifted: the cathodic monophasic pulse and biphasic pulses with interphase delays greater than 800 µs elicited the largest excitation, showing the optimum is intensity-dependent.23
  • The facilitation held for both single pulses and repetitive pulse trains, and pharmacological experiments indicated that trans-synaptic (network) excitation, not just direct membrane depolarization, contributes to the effect.23
  • The authors frame the result as evidence that an optimally timed cathodic-anodic interaction actively enhances activation, going beyond the conventional view that the interphase gap merely prevents the anodic phase from reversing cathodic depolarization.2
  • The practical implication for intracortical microstimulation (ICMS) and cortical visual prostheses is improved neural recruitment efficiency while minimizing delivered charge, which matters for both efficacy and electrode/tissue safety.23
  • The ~600 µs optimum is notably longer than the ~100 µs interphase gaps typically used in clinical ICMS, a gap that a reviewer (Blackrock Neurotech engineer Christopher Lee Hughes) flagged as a potentially important cue for revised stimulation protocols.4
  • Prior work established that a short interphase gap (~100 µs) is enough to eliminate the anodic phase’s charge-reversal effect while preserving charge balance; this new study extends that by showing much longer optimal delays for maximizing circuit activation.54
  • An important caveat is that the experiments were done in slice preparations, so replication in vivo and translation to human perceptual thresholds remain to be demonstrated.46

Footnotes

  1. https://news.google.com/rss/articles/CBMilAFBVV95cUxQbFB5aWR1MC0xNXZBblYzVW52SlRncmItdi14VFRnWi1HZnpkcmhPTkdNelpnUTQzUjdkN1ZXYlc4TkVDaURpYVcxMkhfQ2VsLS1rVXJCb1NnRHVtNzdIVzllQm5EaTRoVUo0d05IVF9KaTZlOFd4X293YmxtQjlYRzB6TEN1VC1tOTA1RnlSTzkxd09S?oc=5 ↩ ↩2 ↩3

  2. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2025.1710221/full ↩ ↩2 ↩3 ↩4 ↩5 ↩6

  3. https://pmc.ncbi.nlm.nih.gov/articles/PMC12833007/ ↩ ↩2 ↩3 ↩4 ↩5

  4. https://www.linkedin.com/posts/christopher-lee-hughes-bci_frontiers-optimal-interphase-delay-in-biphasic-activity-7423425044929970176-Axnm ↩ ↩2 ↩3

  5. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2022.823423/full ↩

  6. https://pubmed.ncbi.nlm.nih.gov/41601545/ ↩

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