Positive and biphasic extracellular waveforms correspond to return currents and axonal spikes

Area of Science:

• Neuroscience
• Computational Neuroscience
• Biophysics

Background:

• Extracellular recordings can detect neural activity, but the origin of non-negative waveforms during action potentials remains unclear.
• Understanding these signals is crucial for interpreting neural circuit function in vivo.

Purpose of the Study:

• Investigate the origin and prevalence of non-negative extracellular spikes in the intact brain.
• Correlate these waveforms with specific neuronal compartments and activities.

Main Methods:

• Extracellular recordings from densely-connected cortical networks in freely-moving mice.
• Analysis of spike waveform shapes and their temporal relationship with neuronal firing.

Main Results:

• Approximately 10% of extracellular waveforms were non-negative.
• Non-negative spikes were associated with return currents near the soma and axonal potentials.
• Isolated biphasic spikes were linked to inhibitory neuronal activity.

Conclusions:

• Non-negative extracellular potentials can indicate specific neural events like axonal activity and return currents.
• Identifying these waveforms enhances understanding of neural mechanisms in physiological and pathological states.
• This research provides a new framework for interpreting extracellular recordings in the brain.