The plantar reflex is the foot’s involuntary response when the sole is stroked firmly from heel to toe, and it is one of the oldest and most widely used tests in neurology. In a healthy adult, the toes curl downward. When the big toe extends upward instead, the response is called the Babinski sign, and it has served as a red flag for damage to the nerve pathways running from the brain down the spinal cord since Joseph Babinski first described it in 1896. Despite being over a century old, this simple bedside test remains a routine part of neurological examinations around the world, though the science behind it is more complicated than most people realize.
What Happens During a Normal Plantar Response
To perform the test, a clinician draws a blunt instrument, often the handle of a reflex hammer or a key, along the outer edge of the sole from the heel toward the little toe, then curves it inward across the ball of the foot. This stimulation activates sensory nerves in the skin, which relay signals up to the spinal cord and brain. The normal adult response is plantar flexion: the toes bend downward, and the foot may pull slightly away from the stimulus. This downgoing toe movement is sometimes called a “flexor” plantar response, even though the toes are technically extending at one joint and flexing at another. The naming convention can be confusing, but the key point is that toes curling under is normal.
The normal plantar reflex is not a single, clean movement. Research has shown that it involves the integration of both flexor and extensor reflex components at the spinal level. In a healthy nervous system, the brain’s descending pathways suppress the extensor component and allow the flexor response to dominate. That suppression is what makes the direction of the big toe so diagnostically useful: when the brain’s control over the spinal cord is interrupted, the suppression lifts, and a different pattern emerges.
The Babinski Sign and What It Reveals
When the big toe extends upward and the smaller toes fan outward in response to sole stimulation, this is the Babinski sign, also called an extensor plantar response. In 1896, Babinski reported that this upgoing toe was a consistent finding among patients with lesions of the pyramidal tract, the nerve pathway responsible for voluntary movement, whether those lesions occurred in the brain’s cortex, subcortex, brainstem, or spinal cord.1PubMed. History of the extensor plantar response: Babinski and Chaddock signs The discovery was a landmark because, for the first time, a clinician had a simple physical test that could distinguish organic neurological disease from functional symptoms.
Electromyographic studies later confirmed that the upgoing toe is produced by a specific muscle: the extensor hallucis longus, a long muscle running along the front of the shin. In patients with a true Babinski sign, stimulating the sole activates this muscle in a way it does not in healthy controls.2PubMed. Babinski response: stimulus and effector The same study found that the type of stimulus matters: electrical stimulation of the sole can sometimes trigger the extensor hallucis longus even in normal subjects, and conversely may fail to activate it in patients who have a clear Babinski sign when tested with a mechanical stroke. This means the traditional stroke along the sole is not interchangeable with an electrical prod, a detail that matters in research settings where standardization is the goal.
Why Babies Have an Upgoing Toe
If an upgoing big toe signals brain or spinal cord trouble in adults, it is reasonable to wonder why the same response is perfectly normal in infants. The answer lies in how the nervous system matures. At birth, the corticospinal tract, the long nerve highway connecting the brain’s motor cortex to the spinal cord, is not yet fully myelinated. Myelin is the insulating sheath that allows nerve signals to travel quickly and precisely. Without full myelination, the brain cannot exert the top-down control needed to suppress the spinal cord’s built-in extensor reflex. The result is that healthy newborns and infants routinely show an upgoing toe when the sole is stroked.
As myelination progresses over the first one to two years of life, the brain gradually gains control over the spinal circuits, and the plantar response flips to the adult pattern of downgoing toes. The timing varies from child to child, but by roughly age two the Babinski sign should have disappeared. When it persists beyond that age, or when it reappears in someone who previously had a normal response, it suggests that something has disrupted the corticospinal tract. Some researchers have drawn a connection between this infantile reflex and primitive grasping reflexes seen in other primates, viewing the Babinski response as an evolutionary relic.3PubMed Central. The Phylogenetic Significance of the Plantar Response in Man
How Reliable Is the Test, Really?
The plantar reflex holds an almost sacred status in clinical neurology, yet the evidence on its reliability is sobering. When researchers have studied how well different examiners agree on what they see, the numbers are consistently low. One study found that the reliability of the Babinski sign was only fair, with a kappa value of 0.30, meaning that two examiners looking at the same patient often disagreed about whether the toe went up or down. By comparison, a simple task like foot tapping had much higher agreement, with a kappa of 0.73.4PubMed. Should the Babinski sign be part of the routine neurologic examination? Agreement with known weakness, used as a proxy for whether the test correctly identified pathology, was only about 56% for the Babinski sign compared with 85% for foot tapping.
A separate study examining agreement among neurologists viewing recorded reflex responses found substantially better numbers, with neurologists achieving a kappa of 0.72, though the study also found that neurologists and medical students used somewhat different visual cues to reach their assessments.5PubMed. The Interrater Reliability of Subjective Assessments of the Babinski Reflex The discrepancy between studies likely comes down to testing conditions: watching a video and making a judgment is a more controlled task than performing the stroke yourself on a live patient whose foot might be twitching, ticklish, or voluntarily withdrawing. In a broader study comparing the Babinski test with several of its clinical variants, the sensitivity of the Babinski itself was about 60%, meaning it missed the abnormality roughly four out of ten times in patients known to have pyramidal tract lesions. Its positive predictive value was around 70%.6PubMed Central. The plantar reflex: A study of observer agreement, sensitivity, and observer bias
None of this means the test is useless, but it does mean clinicians should not treat a single negative Babinski result as proof that the corticospinal tract is intact. The test works best as one piece of a larger puzzle rather than a definitive verdict on its own.
Alternative Ways to Provoke the Same Reflex
Because the classic Babinski stroke along the sole does not always produce a clear response, neurologists have developed several alternative maneuvers that stimulate different skin areas but look for the same upgoing big toe. The best known of these are the Chaddock sign (stroking the outer edge of the foot below the ankle), the Oppenheim sign (pressing firmly down the shin), and the Gordon sign (squeezing the calf muscle). All aim to activate the same spinal reflex arc through different sensory inputs.
How do these alternatives compare? In a study of spastic children with cerebral palsy, the classic Babinski was positive in 75% of cases, while the Gonda-Allen sign caught 90% and the Chaddock caught 74%.7PubMed. “Extensor toe sign” by various methods in spastic children with cerebral palsy In adults, a study assessing consistency found that the Chaddock, Oppenheim, and Gordon reflexes had moderate agreement among examiners, and the Babinski combined with the Chaddock was the most reliable pairing.8PubMed. Consistency of the Babinski reflex and its variants The broader observer-agreement study found comparable performance for the Babinski and the Chaddock, with sensitivity around 55-60% for both, while the Oppenheim lagged behind at 30%.9PubMed Central. The plantar reflex: A study of observer agreement, sensitivity, and observer bias
In practice, many neurologists use the Chaddock as a backup when the Babinski result is equivocal or the patient is too ticklish to tolerate sole stimulation. The Oppenheim and Gordon are less commonly used today but remain in the toolkit. The general consensus is that no single variant is dramatically superior, and using two or three in combination gives the best chance of catching a true extensor response.
The Ticklishness Problem and Other Pitfalls
Anyone who has had their foot stroked by a doctor and immediately pulled it away knows the most common obstacle to a clean plantar reflex test: the foot is a sensitive area, and the withdrawal response to tickling can easily be mistaken for an abnormal reflex. A voluntary withdrawal typically involves the entire leg pulling back with a flexion at the hip and knee, which is different from a true Babinski sign where the big toe extends while the foot stays relatively still. But in practice, distinguishing the two is not always straightforward.
Research has confirmed that sensitivity responses contaminate the plantar reflex and can make interpretation difficult. One study found that in subjects who were ticklish on both sides but had a neurological lesion affecting only one side, knowing the sensitivity pattern on the normal foot improved the examiner’s ability to interpret the response on the affected foot.10PubMed. A systematic and quantitative evaluation of plantar stimulation In other words, comparing both feet gives you a built-in control. If the patient flinches the same way on both sides, it is probably ticklishness. If one side behaves differently, the asymmetry itself becomes the finding.
Other pitfalls include testing with too light a touch (which may not trigger the reflex at all), testing with too sharp an instrument (which produces a pain-withdrawal response rather than a plantar reflex), and testing a patient who is anxious and voluntarily curling their toes. Experienced clinicians learn to adjust their technique, but the subjective nature of these adjustments is part of why inter-examiner agreement remains stubbornly moderate.
When an Upgoing Toe Is Temporary
An extensor plantar response does not always mean permanent structural damage to the nervous system. A variety of temporary and reversible conditions can produce a Babinski sign that goes away once the underlying problem resolves. Although the reflex is best known in conjunction with organic disease involving structural injury to the corticospinal tract, it may appear in a range of toxic and metabolic disturbances, and in some cases the reflex reverts to normal once the underlying condition improves.11PubMed. History of the extensor plantar response: Babinski and Chaddock signs These temporary causes include severe hypoglycemia, hepatic encephalopathy, drug overdoses, seizures (during and shortly after), and deep sedation.
General anesthesia is a particularly well-studied setting. In one study of patients waking up from enflurane-based anesthesia, half had upgoing plantar responses during emergence, and about a quarter of those waking from halothane-based anesthesia showed the same sign. Neither occurred after anesthesia using only nitrous oxide with narcotics.12PubMed. Neurologic changes during awakening from anesthesia A follow-up study comparing enflurane and isoflurane found that upgoing toes and intense muscular spasticity were significantly more common after enflurane, though all abnormalities resolved within an hour.13PubMed. Neurological phenomena during emergence from enflurane or isoflurane anaesthesia These abnormalities tended to peak during the groggy period five to twenty minutes after anesthesia stopped, when patients were still poorly responsive to verbal commands.
The clinical significance is that a Babinski sign found during the immediate post-operative period, or in a patient who has just had a seizure, or in someone with a severe metabolic derangement, cannot automatically be attributed to a stroke or structural lesion. Context matters enormously. A neurologist evaluating such a patient will usually recheck the plantar response once the confounding condition has cleared before drawing conclusions.
Sedation with propofol tells a somewhat different story. A descriptive study of patients under propofol sedation found that extensor plantar responses were present in about 20% of subjects, while in roughly two-thirds the response was indifferent, meaning neither clearly upgoing nor downgoing.14PubMed. Neurological examination in patients undergoing sedation with propofol: a descriptive study The high rate of indifferent responses underscores how difficult the test can be to interpret when the brain is pharmacologically suppressed rather than damaged.
Conditions That Produce a Persistent Babinski Sign
When the upgoing toe is not temporary, the list of possible causes reads like a survey course in neurological disease. Anything that damages the corticospinal tract from the motor cortex down to the spinal cord can do it. Stroke is the most common acute cause: a clot or bleed in the brain destroys neurons or cuts off blood supply to the motor pathways, and the Babinski sign often appears on the side of the body opposite the brain lesion. Multiple sclerosis produces it when demyelinating plaques form along the corticospinal tract. Brain and spinal cord tumors can compress the pathway. Traumatic brain injuries and spinal cord injuries disrupt it mechanically.
Amyotrophic lateral sclerosis, which destroys both upper and lower motor neurons, is a condition where the Babinski sign plays an interesting diagnostic role. In a study of 130 ALS patients, the Babinski sign was positive in about 49%, while hyperreflexia was present in about 69% and spasticity in only about 17%.15PubMed. Relevance of the pyramidal syndrome in amyotrophic lateral sclerosis The fact that the Babinski sign was absent in roughly half of confirmed ALS patients illustrates a broader point: the test has decent specificity for upper motor neuron disease but limited sensitivity. A negative result does not rule out pathology.
Other structural causes include cervical spondylotic myelopathy, where age-related narrowing of the spinal canal compresses the cord, and vitamin B12 deficiency severe enough to cause subacute combined degeneration of the spinal cord. In these cases the Babinski sign may develop gradually, sometimes before the patient notices any weakness or walking difficulty, making it a useful early warning sign during a routine physical exam.
Spinal Shock and the Reflex’s Return
Spinal cord injury presents a paradox: in the acute phase after severe injury, reflexes below the level of the lesion do not increase but instead vanish completely. This phenomenon, called spinal shock, occurs because the sudden disconnection from the brain leaves the spinal cord temporarily unable to generate its normal reflex activity. All reflexes below the injury, including the plantar reflex, go silent.16PubMed Central. Revisit Spinal Shock: Pattern of Reflex Evolution during Spinal Shock
Over days to months, reflexes gradually return, but the pattern and timing are not straightforward. Different types of reflexes recover at different rates, and there has been long-standing debate about which returning reflex should mark the official “end” of spinal shock. Some clinicians define it by the return of the bulbocavernosus reflex (a pelvic reflex), others by the return of deep tendon reflexes in the legs, and still others by the return of bladder reflex activity. As spinal shock resolves, it typically transitions into spasticity, and the Babinski sign emerges as the spinal cord’s circuits begin firing without the brain’s moderating influence. In this context, the appearance of an upgoing toe is actually a sign of recovery at the spinal level, even though it would be considered pathological in someone who had never been injured.
What Brain Imaging Has Added
Modern neuroimaging has begun to fill in the picture of what happens in the brain during plantar stimulation. A functional MRI study using mechanical stimulation of the sole found that it activated the primary sensorimotor cortex and secondary somatosensory cortex on both sides of the brain. The study also identified activity in the supplementary motor area, a region involved in planning and coordinating movement, which was active both during actual plantar stimulation and during mental imagery of walking.17PubMed Central. Brain Activity during Mental Imagery of Gait Versus Gait-Like Plantar Stimulation: A Novel Combined Functional MRI Paradigm to Better Understand Cerebral Gait Control The overlap between plantar stimulation and gait-related brain activity is intriguing because it hints at why the plantar reflex is so closely tied to walking ability. The same brain areas that help you walk are the ones that respond to stimulation of the sole, which may explain why damage to these circuits produces both gait problems and an abnormal plantar reflex simultaneously.
This line of research remains early, and no one is replacing the bedside plantar reflex test with an MRI scan. But the imaging work has helped validate what clinicians have long observed: the reflex is not just a curiosity of spinal cord wiring. It reflects the integrity of a circuit that extends all the way from the foot’s sensory nerves to the highest levels of the brain’s motor planning areas and back down again. When any link in that chain breaks, the toe goes up.