Low-frequency, highly localized extracellular signals recorded from deep within the brain tissue, representing the synchronized input to a neural population.
Key takeaway: Local Field Potentials are essentially carefully recorded "micro-EEGs" taken from inside the parenchyma (the brain matter). While single-unit activity (action potentials) represents the output of localized neurons, the broader LFP primarily represents the input (Excitatory and Inhibitory Post-Synaptic Potentials) arriving at that population.
Physiological Basis
Signal Origins and the Low-Pass SourceWhy LFPs travel farther than spikes.
The brain's extracellular space acts as a low-pass spatial filter. Fast, high-frequency signals like action potentials (1ms duration) decay over very short distances (usually disappearing within 100 microns of the cell body).
Slower events like post-synaptic potentials (10-100ms duration) summate and carry over much larger distances. Thus, an LFP recording represents the sub-threshold activity of thousands of neurons within a roughly ~250-500 micron radius of the electrode tip.
Separating LFP from SpikesThe magic of bandpass filtering.
Microelectrodes implanted in the brain record a raw wideband signal. Engineers isolate LFPs by applying a low-pass filter (typically slicing off everything above 250-300 Hz).
To isolate the spikes (action potentials), they run a high-pass filter (keeping everything above 300 Hz).
Clinical & BCI Applications
Deep Brain Stimulation (DBS) BiomarkersPioneering closed-loop therapies.
In Parkinson's Disease, abnormally high oscillatory power in the Beta band (13-30 Hz) is visible in the LFP recorded directly from implanted DBS electrodes in the subthalamic nucleus (STN).
Modern closed-loop or "adaptive" DBS devices continuously monitor the LFP. When Beta power spikes (indicating motor rigidity), the device turns on stimulation. When Beta power drops (normal movement), the device turns off, saving battery and minimizing side effects.
Intracortical BCI StabilityA robust backup for fading spikes.
In high-performance motor BCIs (like those using Utah Arrays), the foreign body response eventually encapsulates the tiny electrode tips in scar tissue, heavily degrading the amplitude of action potentials (spikes) over a few years.
However, because the LFP signal originates from a much wider spatial pool of neurons, it is remarkably resilient to glial scarring and micromotion. Researchers frequently decode motor intent directly from the High-Gamma LFP when spikes are lost.
Interactive LFP Simulator
An electrode placed deeply inside the brain records the summed extracellular fields of thousands of nearby neurons. Watch how the firing pattern of the local population drastically alters the shape and amplitude of the recorded Local Field Potential.
● Point Source (Neuron Firing)― Summed Extracellular LFP Trace