Scientists have long thought it does this using separate sets of nerve cells.
A new study challenges that idea, finding that most temperature-sensing nerve cells respond to both warming and cooling.
The researchers gently warmed and cooled the mice’s paws while a two-photon microscope tracked each cell’s activity as it changed.
Most cells do both jobsMost cells slowed their activity as the skin warmed, rather than sorting into a clean warm group and a cool group.
Warm and cool cells there even behaved on different clocks – one reacting to absolute temperature and the other to change.
Your skin is constantly monitoring temperature, telling your brain when something feels warm or cool. Scientists have long thought it does this using separate sets of nerve cells.
A new study challenges that idea, finding that most temperature-sensing nerve cells respond to both warming and cooling.
The discovery could reshape how researchers understand nerve disorders that affect sensation.
Watching the nerves
Your skin never stops taking readings. Touch a cold railing or warm water and nerve endings there relay the temperature to your brain within moments.
These cells, called thermoreceptors, have been studied for more than a hundred years, yet how they tell cool from warm stayed unsettled.
Phillip Bokiniec at the University of Queensland (UQ) led a team that imaged hundreds of these cells at once in living mice.
The experiments were run in the lab of James Poulet at the Max Delbrück Center (MDC) in Berlin.
The researchers gently warmed and cooled the mice’s paws while a two-photon microscope tracked each cell’s activity as it changed.
Most cells do both jobs
Most cells slowed their activity as the skin warmed, rather than sorting into a clean warm group and a cool group.
Cells that respond to both warming and cooling were not new to science, but their numbers were a shock.
“Scientists have known about these neurons for years, but they were thought to be relatively rare,” Poulet said.
The imaging showed they make up most of the temperature-sensing population, not a fringe minority.
The same cells also reported the actual temperature of the skin, not merely how fast it was changing.
Warmer skin brought steadily lower activity, and cooler skin steadily higher. The reading was graded, not a simple switch.
That pattern held whether the mice were awake or anesthetized, which ruled out the anesthetic as the cause.
Requiring a single switch
When the researchers blocked TRPM8, the protein long known as the body’s main sensor for cold, the cells stopped responding to cooling. The dampening effect of warmth vanished as well.
TRPM8 had been cast as a dedicated cold detector, one part of a system thought to route warm and cool through different channels. This view has remained widely accepted.
Yet here, a single channel appeared to drive both the increased activity in response to cooling and the decreased activity in response to warming.
One protein, two roles
To test whether one channel really could do both jobs, the team built a computer model of how TRPM8 behaves.
Small changes in the channel’s activity were enough to reproduce the full range of responses seen in the living animals.
The finding supports a form of population coding, where temperature is read from the collective behavior of many cells rather than from separate wires for warm and cool.
“The nervous system appears to use one population of cells that signals both directions of temperature change,” Bokiniec said.
Where signals split
None of this means warm and cool feel the same. The two sensations stay distinct, and the difference appears to be built further along the line, after the first nerves report in.
A separate paper last year traced a dedicated spinal cord circuit that carries cool signals and boosts them on the way to the brain.
In that work, silencing the amplifying cells left mice unable to react to cool, while their responses to warm and to painful cold held steady.
Cool appears to gain its own dedicated pathway somewhere above the skin, even though the sensors in the skin are shared. The same group had already seen this division higher up.
Warm and cool diverge
In an earlier study of the mouse brain, separate cool- and warm-responding neurons were found in a region tied to temperature, along with many neurons that answered to both.
Warm and cool cells there even behaved on different clocks – one reacting to absolute temperature and the other to change.
Put together, the picture is of a sensory system that keeps its options open at the start and commits later.
At the skin, one flexible population registers the full temperature range. The sorting comes later.
Cool and warm pull apart as the signal climbs through the spinal cord and into the brain.
Sensing can often fail
Accurate temperature sensing keeps the body’s core within a safe range, and it falters in a long list of conditions.
Nerve damage from diabetes and chemotherapy, along with multiple sclerosis and spinal cord injury, can distort or dull it, sometimes turning a mild coolness into burning pain.
If one population of cells and one channel carry both cool and warm, a fault in that shared system could unbalance temperature sensing as a whole.
That changes where researchers might look for the breakdown in disorders like diabetic neuropathy.
“Understanding how healthy temperature sensing works is a prerequisite for understanding what goes wrong in disease,” said Clarissa Whitmire.
A shared system at risk
Mapping the healthy system is the step that has to come before any fix. Aging carries a version of the same risk.
Older adults regulate temperature poorly and face real danger in heat waves, and worn thermoreceptor signaling may be part of the reason.
The authors suggest that failing temperature sensation could even act as an early sign of wider nerve decline. What the study establishes is clear.
The skin’s main temperature detectors are generalists, not specialists, and a channel once filed under cold proves to carry warmth as well.
Whether the same rule holds in humans is the next question, along with how these shared signals are sorted in the spinal cord and brain.
The study is published in the journal Neuron.
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