Sensory Systems · Unit 2: Touch

Where Touch Is First Processed: Dorsal Horn and Dorsal Column Nuclei

The textbook draws the dorsal column as a cable that carries touch spikes from the skin to the brainstem. In mice, a dense layer of spinal interneurons and two kinds of inhibition reshape those signals first, and the brainstem receives both a direct and a processed copy. You will be able to describe the recipient zone for low-threshold mechanoreceptors, say what each of three recent papers did and did not show, and compute the latency gap between the two routes.

Watch first Two Copies of One Touch · 2:60

When the skin of a mouse’s hindpaw is indented, the spikes that climb the dorsal column are not all copies of what the skin sent. Some are. Others have already been through the circuitry of the spinal cord. This lesson follows three mouse studies, from 2017 and 2022, that show what that circuitry is, what it does to the signal, and how the brainstem receives both versions.

Every result here is from mice, and the ages matter. The 2017 study used fixed tissue mostly from mice aged 30 to 35 days, spinal slices from mice aged 13 to 21 days, and behaviour in males aged 7 to 12 weeks. In the two 2022 studies the dorsal horn and gracile nucleus were recorded in adult mice under urethane anaesthesia; Chirila and colleagues also recorded primary somatosensory cortex in awake mice. There are no human data in this lesson.

The textbook relay and its missing branch

Touch and pain draws the dorsal column-medial lemniscus pathway: the first-order axon ascends on the same side, synapses in the gracile or cuneate nucleus (together, the dorsal column nuclei, DCN), and the second-order axon crosses in the medulla and reaches the ventral posterolateral thalamus (VPL). That route is correct. This lesson starts below the drawing, in the cord.

The drawing hides two things. First, the touch afferents (low-threshold mechanoreceptors, LTMRs, sorted in the LTMR lesson) end in a layered region of the dorsal horn, and what happens there is a circuit, not a handoff. Second, the dorsal column carries more than primary afferents. Postsynaptic dorsal column (PSDC) neurons are spinal neurons that receive input in the dorsal horn and send an axon up the dorsal column to the DCN. So the brainstem can get a touch signal directly or after spinal processing. Think of a live feed and a mixed recording of the same concert reaching one listener. The anterolateral system is a separate output route and is not covered here.

An atlas of the LTMR recipient zone

LTMR terminals overlap in laminae IIiv to IV of the dorsal horn (laminae are the layers numbered from the surface). The upper border is marked by IB4, a stain for a set of nociceptor terminals. In the mouse lumbar cord, the LTMR recipient zone (LTMR-RZ) was sampled from that border to about 250 µm below it.

Abraira and colleagues (Cell, 2017) described seven excitatory and four inhibitory interneuron populations there. A reporter-defined population is one marked in a mouse line by a gene it expresses, which is a molecular label, not proof of a single cell type (genetic access is covered in tools for development). The excitatory populations were PKCγ, Cbln2, NeuroD4, PVe, CCK, 5HTr6 and Igfbp5. The inhibitory ones were PVi, Kcnip2, Rorβ and Cdh3. Parvalbumin is not an inhibitory marker by default here: PVe is excitatory and PVi is inhibitory.

Three numbers set the scale. The reporter lines together covered an estimated 71 to 82 percent of LTMR-RZ neurons, so the atlas is incomplete. About 70 percent of the neurons intrinsic to the zone were excitatory and about 30 percent inhibitory. And the populations were not private lines. By counting pre- and postsynaptic marker apposition, the authors found that the LTMR subtypes they assayed formed contacts onto between four and eleven interneuron subtypes, and each interneuron subtype sampled input from at least one to three LTMR classes. The interneurons also received descending corticospinal input, and PSDC neurons received their excitatory input mainly from local interneurons of the zone.

In spinal slices, the populations fired differently when current was injected. Cbln2 neurons burst at the start and PKCγ neurons spiked after a delay. Among inhibitory neurons, PVi cells fired tonically, Kcnip2 and Rorβ cells after a delay, and Cdh3 cells with gaps. PVi and Cdh3 neurons formed axo-axonic contacts (synapses onto another neuron’s axon terminal) on sensory terminals, consistent with presynaptic inhibition of the afferents, the mechanism of synaptic integration.

Did any of it matter for behaviour? The authors silenced spinal CCK or Rorβ lineages in mice and tested a texture version of the novel object recognition test (NORT), in which a mouse that remembers an object explores a new one more. Both silenced groups lost the preference for the newly textured object, and kept the preference when objects differed in colour and shape. Read this carefully. A lineage includes every cell that ever expressed the marker, so the silencing is not acute and not one pure type. It shows these lineages contribute to the task, not that each subtype is needed.

AI-generated illustration: a top-down mouse arena with two identical-shaped objects, one smooth and one ridged, and a smaller inset arena with a cube and a cylinder that differ in colour and shape. The new object in each is ringed in gold.
Abraira and colleagues tested a texture version of the novel object recognition test, in which a mouse that remembers an object explores a new one more. Mice with CCK or Rorβ lineages silenced lost the preference for the newly textured object but kept it when objects differed in colour and shape.

Convergence and two kinds of inhibition

An atlas lists who is present. Chirila and colleagues (Cell, 2022) asked what the circuit does to a touch signal. They recorded from the dorsal horn of adult, urethane-anaesthetized mice (older than 6 weeks) while the skin was indented, and sorted the responses into six functional profiles. Those are response clusters, not six cell types. Individual neurons received convergent input from low-threshold and high-threshold mechanoreceptors, the latter being afferents that respond only to stronger, often damaging, stimuli.

Two inhibitory motifs shaped the output of PSDC neurons.

  • Feedforward inhibition. The same afferent input that excites a PSDC neuron also excites an interneuron that inhibits it, so excitation is followed by inhibition. Rorβ interneurons supplied glycinergic feedforward inhibition onto PSDC neurons.
  • Presynaptic inhibition. Inhibition is applied to the afferent terminal, scaling down the transmitter it releases. PVi neurons took part in presynaptic inhibition that depended on GABA-A receptors.
AI-generated illustration: two cell-level diagrams. Left, an afferent excites both a gold PSDC neuron and a Rorβ interneuron, which then inhibits the PSDC neuron. Right, a PVi interneuron inhibits the afferent terminal itself through GABA-A receptors, so the afferent's excitatory arrow to the PSDC neuron is thinner.
Feedforward inhibition follows the same afferent input onto the PSDC neuron (Rorβ interneurons, glycinergic), while presynaptic inhibition acts on the afferent terminal and scales down its transmitter release (PVi neurons, GABA-A dependent). Disrupting either enlarged PSDC receptive fields in Chirila and colleagues' mice.

Disrupting either motif enlarged PSDC receptive fields, and loss of presynaptic inhibition produced after-discharge, continued firing after the end of a step indentation. Disrupting feedforward inhibition also changed touch responses in primary somatosensory cortex (S1) of awake mice, and those mice showed tactile over-reactivity and a texture discrimination deficit. The limits are plain: the dorsal horn and PSDC recordings were made in anaesthetized mice, and both disruptions were chronic conditional knockouts (Vgat deleted in Rorβ neurons for feedforward inhibition, and the GABA-A β3 subunit gene deleted in sensory neurons for presynaptic inhibition), which cannot be assumed to isolate acute circuit function. The dorsal column is therefore not a simple relay.

Two routes to the brainstem that meet again

Turecek, Lehnert and Ginty (Nature, 2022) recorded in the hindlimb part of the gracile nucleus of adult, urethane-anaesthetized mice (older than 5 weeks, both sexes). Neurons were identified by antidromic activation, stimulating a projection target and testing for collision, as either VPL-projecting or inferior colliculus-projecting. The direct pathway is primary Aβ-LTMR axons contacting DCN neurons. The indirect pathway reaches the DCN through PSDC neurons.

Direct input conveyed vibration with high temporal precision. Most VPL-projecting neurons entrained to vibration only within a narrow range below 150 Hz, while most neurons that projected to the inferior colliculus phase-locked from 10 to 500 Hz, the highest frequency tested. The indirect input supported coding of sustained contact intensity, extending to high forces, tested with a blunt 1-mm probe from 1 to 300 mN. Both pathways contributed to responses to gentle displacement, so “direct means vibration and indirect means light touch” is too simple. The authors also could not detect a clear core-shell organization in the mouse gracile recordings, so the split here is direct versus indirect route, not a map of submodalities across the nucleus.

To separate the routes, the authors silenced afferent terminals reversibly with the light-gated ACR1, which was validated only for gentle stimuli of about 20 to 30 mN or less, and applied glutamate receptor antagonists to the lumbar cord to suppress the indirect route while the direct axons kept conducting. That drug is not specific to PSDC neurons. Blocking lumbar excitatory transmission almost eliminated sustained indentation firing in most recorded units. And the two routes meet: direct and indirect inputs to single VPL-projecting neurons had highly aligned receptive fields, and these neurons had small excitatory fields surrounded by larger suppressive regions.

Worked problem, part (a): can the two inputs be told apart by timing? Suppose a gracile neuron receives both inputs from a mouse hindpaw. These are illustrative numbers, not measurements, and the assumptions are constant velocity and conduction plus synaptic delay only (see the action potential lesson).

t = L / v

  • Direct: 0.08 m at 16 m/s = 0.005 s = 5.0 ms.
  • Indirect, paw to lumbar cord: 0.04 m at 16 m/s = 2.5 ms.
  • Indirect, two spinal synapses at an assumed 1 ms each = 2.0 ms.
  • Indirect, PSDC axon: 0.04 m at an assumed 8 m/s = 5.0 ms.
  • Indirect total: 2.5 + 2.0 + 5.0 = 9.5 ms. Difference: 9.5 − 5.0 = 4.5 ms.

The indirect input arrives about 4.5 ms later, a gap large enough to separate the two components in a recording. Lumbar excitatory blockade should remove the indirect input. Turecek and colleagues did not measure latencies this way: they found that blockade nearly abolished sustained-indentation firing in most units and also raised the onset threshold, so the indirect route is not only a late add-on.

Two routes to the gracile nucleus — a latency sketch⚙ original · interactive
Stimulated paw’s side Opposite side Gracile nucleus VPL (thalamus) second-order axon crosses in the medulla to VPL dorsal column LTMR recipient zone (lumbar dorsal horn) antagonists applied direct 0.08 m 5.0 ms PSDC axon 0.04 m 2 synapses 1.0 ms each paw to cord, 0.04 m 2.5 ms dorsal root ganglion Hindpaw (stimulated)

Left and right are the mouse’s own. Everything below the medulla is on the stimulated paw’s side; nothing crosses in the cord. Only the second-order axon crosses, in the medulla. The direct and indirect afferents are drawn as separate lines for clarity.

Direct, t = L / v
Indirect: afferent + synapses + PSDC axon
Indirect minus direct

In this sketch: illustrative lengths and velocities, not measurements; constant speed; conduction plus synaptic delay only; anaesthetized adult mouse logic. The rule to keep is t = L / v for each stage, then add the synaptic delays.

Part (b), real data. Abraira counted 2.9 ± 0.1 (mean ± SEM) axo-axonic inhibitory contacts per sensory terminal in fixed mouse tissue, of which 1.5 ± 0.1 were from PVi neurons. 1.5 / 2.9 = 0.52, so about 52 percent of the contacts. These are contact counts, not conductances, so they do not say PVi neurons supply half of the inhibition.

When inhibition fails

If inhibition holds back touch from other circuits, loss of inhibition could let it reach them. Duan and colleagues (Cell, 2014) tested that in mice, and spinal circuits that gate pain covers the work in full. Ablating somatostatin-lineage excitatory spinal neurons impaired mechanical pain behaviours, and dynorphin-lineage inhibitory neurons gated Aβ input from activating the somatostatin neurons (ablation in vivo; slice recordings from mice aged 23 to 30 days). This is a separate circuit result from the PSDC experiments. An enlarged PSDC receptive field is not allodynia, and the blunt 300 mN indentations did not evoke pain behaviour in awake mice. A later lesson takes touch over-reactivity in autism models further.

Design problem

Chirila and colleagues found that PSDC receptive fields grow when presynaptic inhibition is lost. Design an experiment to show that this matters for perception, and say what would be needed in people.

One way to do it

Silence PVi neurons acutely in adult mice, with a cell-type-restricted tool, not a developmental or germline lineage deletion, which can change the cord’s wiring. Record PSDC neurons in awake mice, not under urethane, to check that the field enlargement survives without anaesthesia. Measure tactile acuity behaviourally, for example discrimination of closely spaced textures, paired with a control that does not depend on texture, like Abraira’s colour and shape object test, so a general change in exploration is not mistaken for a tactile one. Remember that a spinal drug blockade is not PSDC-specific, so a drug result must not be read as one. Finally, mouse data do not transfer by default. In people, you would need psychophysical acuity measures and a way to change spinal inhibition safely, and a result would still be limited to that preparation.

How we measure it

Reporter lines and intersectional silencing

Mouse lines in which a genetic driver switches on a fluorescent reporter label cells that express a marker gene. Combining two drivers restricts the label, or a silencing tool such as tetanus toxin, to cells in the spinal cord. The result tells you which cells have the marker and, for silencing, which behaviours need that lineage, not that the marked cells are one pure cell type.

Whole-cell patch clamp in spinal slices

A glass pipette records voltage or current from a single labelled neuron in a thin slice of mouse spinal cord. Injecting current shows the cell's firing pattern, such as an initial burst, delayed spiking, tonic firing or gaps. The preparation is from young animals and cut off from most of its inputs, although some slices keep dorsal roots attached so afferents can be stimulated.

In vivo multielectrode recording with antidromic identification

Electrode arrays record spikes in anaesthetized mice while a motorized probe indents or vibrates the skin. Stimulating a neuron's output axon and checking that the spike collides with a spontaneous one proves that the neuron projects there. This labels neurons by target, such as thalamus or inferior colliculus.

Reversible input silencing

A light-gated silencer (ACR1) in afferent terminals, or a glutamate receptor antagonist applied to the lumbar cord, removes one route's contribution to a recorded neuron while leaving the other route in place. Each tool has limits of efficacy and specificity that must be checked before reading the result.

Finish line

Test yourself

8 questions

Practice and MCAT-style, with explained answers.

Next · Lesson 9

Touch Over-reactivity in Autism Models

In one experiment, deleting a gene from peripheral sensory neurons, but not from the brain, was enough to change a mouse's behaviour in anxiety-like and social assays.

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← Lesson 7 · Hairy Skin, Stroking and Affective Touch

Victoria Abraira

Victoria Abraira

First author of the 2017 Cell study that mapped the recipient zone of low-threshold mechanoreceptors in the mouse lumbar dorsal horn into reporter-defined excitatory and inhibitory interneuron populations and tested two of the lineages in a texture task.

The textbook dorsal horn was a relay drawn as a few boxes. Abraira and colleagues set out to count what was inside the part of the dorsal horn where touch afferents end. They worked in the mouse lumbar cord, using reporter lines to label populations by the genes they express, antibodies against pre- and postsynaptic markers to see which terminals touched which cells, and whole-cell recordings in spinal slices to see how the cells fire. The result was seven excitatory and four inhibitory populations that together covered roughly 71 to 82 percent of the neurons in the zone, with the subtypes sampling input from one to three classes of touch afferent. The team then silenced two spinal lineages and tested mice on a task in which they explore objects of different texture. The paper named populations that a recording or a silencing experiment can be aimed at, in place of the zone as a whole.

✓ verbatim Abraira et al., 'The cellular and synaptic architecture of the mechanosensory dorsal horn', Cell, 2017 (online 29 December 2016), doi 10.1016/j.cell.2016.12.010.
Anda Chirila

Anda Chirila

First author of the 2022 Cell study that recorded the mouse dorsal horn in vivo, sorted its responses to skin indentation into six profiles, and tested two inhibitory motifs that shape the output to the brainstem.

An atlas shows who is present; it does not show what they do to a signal. Chirila and colleagues recorded from the dorsal horn of adult, urethane-anaesthetized mice while the skin was indented, and grouped what they saw into six functional response profiles. They found that individual neurons receive signals from both low-threshold and high-threshold mechanoreceptors. They then asked how two inhibitory motifs change the output of postsynaptic dorsal column neurons, the spinal cells that send an axon up toward the brainstem. Interneurons marked by the gene Rorb provided glycinergic feedforward inhibition onto those output cells, and parvalbumin-positive inhibitory interneurons took part in GABA-A receptor dependent presynaptic inhibition of the afferents. Disrupting either motif enlarged receptive fields, and disrupting feedforward inhibition also changed touch responses in primary somatosensory cortex. The paper turned the dorsal horn from a place that holds cell types into a place with measurable computations.

✓ verbatim Chirila et al., 'Mechanoreceptor signal convergence and transformation in the dorsal horn flexibly shape a diversity of outputs to the brain', Cell, 2022, doi 10.1016/j.cell.2022.10.012.
Josef Turecek

Josef Turecek

First author, with Brendan Lehnert and David Ginty, of the 2022 Nature study that separated a direct and an indirect pathway through the dorsal columns to the mouse gracile nucleus and showed that they reconverge on the same output neurons.

The dorsal column holds two kinds of axon: primary afferents that run to the brainstem without a synapse, and axons of spinal neurons that have already processed the signal. Turecek, Lehnert and Ginty recorded in the hindlimb part of the gracile nucleus of adult, urethane-anaesthetized mice, identified which neurons projected to the thalamus or to the inferior colliculus by activating their axons, and used a light-gated silencer on afferent terminals and a drug applied to the lumbar cord to separate the two routes. The direct route carried vibration with precise timing. The indirect route carried sustained indentation up to high forces. Both contributed to gentle displacement, and the two inputs to a single thalamus-projecting neuron had aligned receptive fields. The study replaced a single relay with two complementary inputs, and gave a way to ask what each contributes to what the cortex receives.

✓ verbatim Turecek, Lehnert & Ginty, 'The encoding of touch by somatotopically aligned dorsal column subdivisions', Nature, 2022, doi 10.1038/s41586-022-05470-x.
David Ginty

David Ginty

Named author on all three studies in this lesson, which move from a cell-type map of the dorsal horn, to its computations in vivo, to the two routes into the brainstem.

Read in order, the three papers form one argument made at three scales. The 2017 study asked which cells are in the zone where touch afferents end, and gave named populations with their synaptic partners. The first 2022 study asked what the spinal circuit does to a touch signal while the animal is being stimulated, and found convergence plus two kinds of inhibition that change the size and timing of the output. The second 2022 study asked what the brainstem receives, and found that it receives both the afferent signal and the spinal output, aligned on the same cells. The first 2022 study used genetic tools and methods from the atlas, and the second asked what the spinal output adds to the signal that reaches the brainstem, using its own tools. What the three do not yet supply is a recording of PSDC or gracile neurons in awake animals, or a measurement in people.

✓ verbatim Abraira et al., Cell (2017), doi 10.1016/j.cell.2016.12.010; Chirila et al., Cell (2022), doi 10.1016/j.cell.2022.10.012; Turecek, Lehnert & Ginty, Nature (2022), doi 10.1038/s41586-022-05470-x.
Test yourself
Question 1 of 8 Score 0 / 0

In the dorsal column, which description fits a postsynaptic dorsal column (PSDC) neuron?
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Every structure, slide, simulation, and clip on this page is listed below with the source it came from. None of the 3D structures is drawn by hand or by AI: each one loads by accession ID from RCSB PDB or PubChem. This panel is generated from the lesson's own data file, so what it lists is what the page loads.

Simulations

  • Two routes, two arrival times · Original interactive — Biochemistrypedia (Deppmann Lab).

Scientist profiles & quotes

  • Victoria Abraira — Abraira et al., 'The cellular and synaptic architecture of the mechanosensory dorsal horn', Cell, 2017 (online 29 December 2016), doi 10.1016/j.cell.2016.12.010.
  • Anda Chirila — Chirila et al., 'Mechanoreceptor signal convergence and transformation in the dorsal horn flexibly shape a diversity of outputs to the brain', Cell, 2022, doi 10.1016/j.cell.2022.10.012.
  • Josef Turecek — Turecek, Lehnert & Ginty, 'The encoding of touch by somatotopically aligned dorsal column subdivisions', Nature, 2022, doi 10.1038/s41586-022-05470-x.
  • David Ginty — Abraira et al., Cell (2017), doi 10.1016/j.cell.2016.12.010; Chirila et al., Cell (2022), doi 10.1016/j.cell.2022.10.012; Turecek, Lehnert & Ginty, Nature (2022), doi 10.1038/s41586-022-05470-x.

Quotes are verbatim from the cited source. Profile text is original to this site and was checked against the sources cited.

Animated explainer

Two Copies of One Touch · narration: an AI narrator voice (Gemini, Charon) reading narration written from this lesson's text · animation: AI-generated in code (Manim) by Claude, a schematic with no drawn molecular structures, plots computed from their equations · captions from the narration script.

Images & figures

2 illustrations in this lesson are AI-generated: drawn by an image model from a written spec, then checked by a separate AI judge against the spec and the lesson text. None shows a chemical structure or data.

  • a top-down mouse arena with two identical-shaped objects, one smooth and one ridged, and a smaller inset arena with a cube and a cylinder that differ in colour and shape. The new object in each is ringed in gold.
  • two cell-level diagrams. Left, an afferent excites both a gold PSDC neuron and a Rorβ interneuron, which then inhibits the PSDC neuron. Right, a PVi interneuron inhibits the afferent terminal itself through GABA-A receptors, so the afferent's excitatory arrow to the PSDC neuron is thinner.

Every 3D structure is rendered live from an accession ID, and every plot is drawn from its equation in the browser.

integrity Machines check the mechanics. The build confirms that every local file exists, that every question's answer key points at a real choice, and that any AI-generated scientific figure names the person who checked it; a weekly job re-resolves every accession ID against its database. Questions are original; MCAT-style items are written for this site and are not real AAMC questions. Banned sources (the Tymoczko textbook, publisher decks, copyrighted figures) are not used.

Like I'm five

Touch does not go straight from your skin to your brain like a note passed along a row of desks. Close to the start, in your spinal cord, there is a busy crowd of helper cells. Some of them mix messages from different parts of the skin, and some of them quiet the messages down. A second copy of the message also goes up a faster direct way, and the two copies meet again at the top of the cord.
High school

Nerve cells in the skin that feel gentle touch send their signals into the spinal cord. In mice, the area where they arrive is full of many types of nerve cell, about seven out of ten of them excitatory and the rest inhibitory. These cells combine signals and also turn some of them down, and then send a new version up the spinal cord to the brainstem. A direct copy of the original signal travels up as well. The direct copy is good at fast vibration and the processed copy is good at telling how hard something is pressing. Both arrive at the same brainstem cells and match up to the same patch of skin.
College

In the mouse lumbar dorsal horn, low-threshold mechanoreceptor (LTMR) terminals overlap in a recipient zone about 250 µm deep below the IB4 border. Abraira and colleagues (2017) split its neurons into seven excitatory and four inhibitory reporter-defined populations, about 70 percent of the zone's neurons being excitatory, and found that postsynaptic dorsal column (PSDC) neurons receive most of their counted synaptic input from local interneurons. In anaesthetized adult mice, Chirila and colleagues (2022) showed convergence of LTMR and high-threshold input, glycinergic feedforward inhibition from Rorβ interneurons, and GABA-A dependent presynaptic inhibition involving PVi neurons, all of which shape PSDC output. Turecek, Lehnert and Ginty (2022) showed that the gracile nucleus receives a direct Aβ-LTMR input with precise vibration timing and an indirect PSDC input that carries sustained force, and the two align on thalamus-projecting neurons.
Graduate

The three studies make a stack of claims at different levels of evidence, and the lesson's main discipline is to keep them apart. The atlas has 71 to 82 percent coverage and mixed ages (fixed tissue at P30 to 35, slices at P13 to 21, behaviour at 7 to 12 weeks in males), and its silencing experiments are lineage-wide, so they show contribution to a texture task and not necessity of any single subtype. The Chirila response profiles are functional clusters, not cell types, and the Chirila and Turecek recordings are from urethane-anaesthetized adults, which limits what can be said about awake behaviour (Chirila did record cortex and test behaviour in awake mice, but after chronic knockouts). Turecek's afferent silencing was validated only up to about 20 to 30 mN, and lumbar antagonists are not PSDC-specific. Open question: do acute, cell-type-restricted perturbations of PVi or Rorβ neurons in awake mice change tactile acuity, and how much of the cortical effect seen in S1 is carried by the dorsal column rather than by other spinal outputs?
A control for a lazy mouse

When the spinal CCK or Rorβ lineages were silenced, mice no longer preferred a newly textured object over a familiar one. A deficit like that could mean a failure of touch, or of memory, motivation or movement. The authors tested the same mice on objects that differed in colour and shape instead of texture, and they still preferred the novel one. That control does not say what the lineages compute. It rules out a mouse that has simply stopped exploring, which is why a behavioural result in this field needs a non-tactile twin of the assay.

— Abraira et al., Cell (2017), doi 10.1016/j.cell.2016.12.010.
A force that did not hurt

The indirect route carries sustained indentation up to high forces, which invites the thought that it is a pain pathway. The authors checked. They used a blunt probe 1 mm in diameter, with forces of 1 to 300 mN in the recordings, and in a control assay in awake mice the high-force indentation did not evoke pain-related behaviour. Strong firing at high force is therefore not evidence of pain, and an anaesthetized neuron's spikes cannot tell you what the animal would feel.

— Turecek, Lehnert & Ginty, Nature (2022), doi 10.1038/s41586-022-05470-x.
Eleven populations, not all of them

The atlas reports seven excitatory and four inhibitory populations, and it is tempting to read eleven as the number of cell types in the zone. The paper estimates that the reporter lines together cover 71 to 82 percent of the neurons there. Neurons that no line marks are not counted, and a molecular population is not the same thing as a functional cell type. A count of populations is a count of the genetic handles used, not of the cells there are.

— Abraira et al., Cell (2017), doi 10.1016/j.cell.2016.12.010.

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