The operating point of the cortex: neurons as large deviation detectors

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Spiking neurons convert analog intracellular signals into action potentials.
• The generator potential reflects neuronal drive, transformed into firing rate via a static nonlinearity.
• Adaptive mechanisms adjust the generator potential's mean and standard deviation (SD), defining the operating point for spike generation.

Purpose of the Study:

• Investigate how adaptive mechanisms tune the neuronal operating point in the cortex.
• Contrast cortical operating point tuning with that of early sensory pathways.
• Determine the functional consequences of the observed cortical operating point.

Main Methods:

• Analysis of neuronal activity and generator potentials in the cortex.
• Modeling of neuronal firing rate based on generator potential and operating point.
• Comparison of information transmission and signal detection under different operating point conditions.

Main Results:

• Cortical operating points are tuned such that neurons respond to large excursions of the generator potential above its mean.
• The distance from the mean generator potential to spike threshold is approximately 1 SD of ongoing activity.
• Signals above threshold are amplified linearly without saturation, and the operating point remains invariant to stimulus contrast changes.

Conclusions:

• The cortical operating regimen is optimized for detecting signals in background noise.
• This operating point enhances spike response selectivity (the "iceberg effect"), improving signal detection over raw generator potential changes.
• This strategy prioritizes signal detection and selectivity over maximizing total information transmission.