Sensitivity to perturbations in vivo implies high noise and suggests rate coding in cortex

Area of Science:

• Neuroscience
• Computational Neuroscience

Background:

• Neural activity variability is a known phenomenon, but its interpretation as noise or information remains debated.
• Understanding the source and meaning of neural variability is crucial for deciphering brain function.

Purpose of the Study:

• To investigate whether small perturbations in cortical networks are amplified.
• To determine the implications of this amplification for neural coding and information processing.

Main Methods:

• In vivo whole-cell patch-clamp recordings in rat barrel cortex.
• Simultaneous intra- and extracellular recordings.
• Theoretical analysis of neural network dynamics.

Main Results:

• A single extra spike in one neuron led to approximately 28 additional spikes in postsynaptic targets.
• A single neuron spike caused a detectable increase in the firing rate of the local network.
• Amplification results in intrinsic, stimulus-independent membrane potential variations of +/-2.2-4.5 mV, interpreted as noise.

Conclusions:

• Cortical networks exhibit significant amplification of neural activity perturbations.
• This amplification generates intrinsic noise, suggesting that complex signaling events like synfire chains are rare.
• Findings support the hypothesis that the cortex primarily employs a rate code for reliable neural computations.