Sensory Afferents Use Different Coding Strategies for Heat and Cold

Area of Science:

• Neuroscience
• Sensory Biology

Background:

• Primary afferents convert environmental stimuli into electrical signals for sensation.
• Understanding how these afferent populations encode somatosensory information is crucial but largely unknown.

Purpose of the Study:

• To investigate the encoding mechanisms of different somatosensory inputs by dorsal root ganglion (DRG) neurons.
• To differentiate how thermal and mechanical stimuli are represented at the neural population level.

Main Methods:

• Utilized two-photon calcium imaging to monitor activity from thousands of DRG neurons in anesthetized mice.
• Applied controlled mechanical and thermal stimuli to the hind paws of the mice during imaging.

Main Results:

• Approximately 50% of DRG neurons were found to be polymodal, responding to multiple stimulus types.
• Heat and cold stimuli are encoded distinctly: heat elicits graded responses at both single-neuron and population levels.
• Cold stimuli are primarily encoded through combinatorial activation of cooling-sensitive neurons, not graded responses.

Conclusions:

• Somatosensory input is encoded by distinct combinations of diversely tuned neurons, enabling rich population-level coding.
• Neural coding for temperature differs significantly between heating and cooling stimuli.
• Polymodal neurons play a significant role in integrating diverse sensory information.