SI neuron response variability is stimulus tuned and NMDA receptor dependent

Area of Science:

• Neuroscience
• Somatosensory System
• Neural Coding

Background:

• Single skin mechanoreceptive afferents (sMRAs) and anterior parietal cortical (SI) neurons respond to mechanical stimuli.
• Understanding the variability in neural responses is crucial for deciphering sensory information processing.

Purpose of the Study:

• To investigate the characteristics of intertrial response variation in SI neurons.
• To determine the influence of stimulus parameters and N-methyl-D-aspartate (NMDA) receptor activity on this variation.

Main Methods:

• Recorded spike discharge activity from sMRAs and SI neurons in anesthetized monkeys (Macaca fascicularis) using skin brushing stimuli at various velocities and positions.
• Quantified mean firing rate (MFR) and intertrial response variation (CV) for each neuron and stimulus condition.
• Administered phencyclidine (PCP) and ketamine (KET) to block NMDA receptors and assessed their effects on CV and MFR.

Main Results:

• SI neuron responses showed greater intertrial variation (CVSI) compared to sMRAs (CVsMRA).
• CVSI was stimulus-tuned, being lowest when stimuli traversed the receptive field center at optimal velocities (e.g., 10 cm/s).
• NMDA receptor blockade with PCP or KET consistently reduced CVSI, with greater reductions observed for higher baseline CVSI.

Conclusions:

• Intertrial response variation in SI neurons is dependent on stimulus properties, particularly velocity and location within the receptive field.
• NMDA receptor activity plays a significant role in modulating intertrial response variation in the somatosensory cortex.
• Minimizing NMDA receptor contribution reduces response variability, suggesting a mechanism for enhanced sensory coding precision.