Rate code and temporal code for frequency of whisker stimulation in rat primary and secondary somatic sensory cortex

Area of Science:

• Neuroscience
• Sensory Processing
• Somatosensory Cortex

Background:

• The somatosensory cortex processes tactile information, with whiskers playing a key role in rodent sensory perception.
• Understanding neuronal responses to varying stimulus frequencies is crucial for deciphering sensory coding.

Purpose of the Study:

• To investigate neuronal responses to a range of whisker stimulation frequencies in rat primary (S1) and secondary (S2) somatosensory cortex.
• To identify and characterize neurons that respond across the entire frequency spectrum of whisker stimulation.

Main Methods:

• Recorded responses from 479 neurons in S1 (barrels and septa) and S2 of urethane-anesthetized rats.
• Deflected five whiskers using air puffs at frequencies from 1 to 18 Hz.
• Analyzed neuronal discharge rates and temporal accuracy in response to stimulation.

Main Results:

• Identified "full responders" (5% of neurons) responsive across all tested frequencies.
• 60% of neurons responded only below 6 Hz, and 35% remained subthreshold.
• Full responders showed peak responsiveness at 1 Hz and greatest synchrony at 18 Hz.
• Barrel cells excelled in temporal accuracy between 3-15 Hz; septum cells maintained accuracy across frequencies.
• S2 cells showed lowest temporal accuracy, sensitive only to frequencies below 6 Hz.

Conclusions:

• Full responders in S1 septa are suited for encoding high-frequency whisker stimuli via timing and discharge rate.
• Barrel cells are optimal for mid-range frequency coding, while S2 cells are sensitive to low frequencies.
• Neuronal discharge patterns may explain observed blood flow changes with increasing stimulus frequency.