Noise enables multiplexed coding of the amplitude & frequency of periodic signals in mouse primary somatosensory cortex

Kamaleddin, Mohammad Amin  1, 2  ;   Prescott, Steven A.  1, 2, 3    

1.   Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada;    2.   Institute of Biomaterials & Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada;    3.   Department of Physiology, University of Toronto, Toronto, Ontario, Canada  

One of the greatest challenges facing neuroscience is to understand how sensory stimuli are encoded in the brain, resulting in sensory perception. Different spatial and temporal features of neuronal spiking represent sensory information about external stimuli to the brain; however, the extent to which this information is being used by the brain for making perceptual decisions is elusive. When a neuron responds to a sensory stimulus, two fundamental codes may transmit the information: 1) the spike rate defined as the total number of spikes normalized by time; and 2) the spike timing defined as a detailed, millisecond-scale temporal structure of the spike pattern.

For vibrotactile stimulation driven by periodic signals of 100-600 Hz, emerging evidence suggests that spike rate and timing can both be used. Notably, pyramidal neurons in primary somatosensory cortex (S1) fire at rates << 100 Hz; temporal features of the spikes might be combined with spike rate to convey information. However, the presence of background noise is a defining property of cortical neurons. Many studies demonstrated that pyramidal neurons in the cortex are constantly bombarded by synaptic inputs, which can be approximated as colored noise. On one hand, it has been shown that a small perturbation in the background activity could result in the variation in the membrane potential independently from the stimulus and disrupt spike timing. On the other hand, noise has been shown to improve response fidelity. Thus, the extent to which noise might play a beneficial vs. detrimental role in rate and temporal coding of spikes, especially in cortical neurons, is yet to be fully resolved.