Primitive Reflexes in Adults: What Causes Their Return?

Primitive reflexes are automatic movement patterns that every human is born with, and while most fade during the first year of life as the brain matures, they can and do reappear in adults. These re-emergent reflexes, sometimes called “frontal release signs,” surface when the higher brain regions that normally keep them in check are weakened by injury, disease, or sometimes just aging. Their presence in an adult is one of the oldest bedside clues in neurology, but interpreting what they actually mean turns out to be far less straightforward than textbooks once suggested.

Why These Reflexes Disappear and Come Back

In infancy, reflexes like grasping, sucking, and the startle-like Moro response serve clear survival purposes. A newborn’s grasp reflex helps it cling; the rooting and sucking reflexes help it feed. As the cerebral cortex develops over the first months of life, these brainstem-driven patterns get suppressed. They do not vanish from the nervous system entirely. The circuits that produce them remain wired in, held in check by inhibitory signals from higher cortical areas, particularly the frontal lobes.

When something damages or degrades those frontal regions, the old circuits can reassert themselves. This is the “release” in “frontal release signs,” meaning the primitive reflex is released from cortical inhibition. Research on conditions like encephalopathies has demonstrated that these reflexes represent exactly that: the emergence of hardwired responses once the cortex can no longer keep them suppressed.¹ A 2026 study in JAMA Network Open described these signs as reflexes that “regress with brain maturation and reappear in the setting of brain injury or neurodegeneration.”²

How Common They Are in Healthy Adults

Here is where intuition gets it wrong. Many people assume that finding a primitive reflex in an adult automatically signals serious brain disease. In reality, a substantial proportion of healthy adults have at least one detectable primitive reflex, and the proportion climbs with age. A population-based study from the Maastricht Aging Study found that roughly half of adults in their twenties through forties already had at least one primitive reflex present. By the time participants were between 65 and 85 years old, about three-quarters showed at least one.³

Critically, in that same study, the presence, strength, and persistence of these reflexes had no relationship to cognitive performance at baseline or over a six-year follow-up period.⁴ A separate study of 68 healthy older volunteers found primitive reflexes in half the group and noted a link to small incidental brain lesions on MRI, but no difference in blood flow, brain shrinkage, or intellectual ability between those with and without the reflexes.⁵

So finding one or even two of these reflexes during a routine exam does not, on its own, mean anything is wrong. Context matters enormously: how many reflexes are present, how strong they are, whether other neurological signs accompany them, and what symptoms the person is experiencing.

The Most Commonly Tested Reflexes

Neurologists typically look for a handful of specific primitive reflexes in adults. Each is elicited in a slightly different way, and each has somewhat different clinical associations.

Glabellar tap (Myerson’s sign): The examiner taps repeatedly between the eyebrows. Normally, a person blinks the first few times and then stops responding. When the blink persists without fading, it is called a “non-habituating” glabellar response. This sign has long been associated with Parkinson’s disease, though its diagnostic accuracy is limited. One study found it had about 78% sensitivity for distinguishing Parkinson’s from essential tremor, but only about 36% specificity, meaning many people without Parkinson’s also test positive.⁶ Video-based research has confirmed that people with Parkinson’s simply do not habituate to the tapping, and dopaminergic medication does not change this.⁷
Palmomental reflex: Scratching the palm of the hand causes a brief twitch of the chin muscle on the same side. This is one of the most commonly found primitive reflexes in healthy adults, which limits its usefulness as a standalone diagnostic sign. However, in people younger than 80, it does appear to be more frequent in Alzheimer’s disease compared to controls, and it may show up as early as two years before diagnosis.⁸
Grasp reflex: Stroking the palm triggers an involuntary gripping response. Among the primitive reflexes, the grasp reflex tends to be the most clinically significant in adults because it is rarely found in healthy people and is strongly associated with frontal lobe damage. Research into its neuroanatomy found that grasping occurred in about 70% of patients with damage to the medial frontal areas, particularly the cingulate gyrus, but only about a quarter of those with damage limited to the lateral motor regions.⁹
Snout and suck reflexes: The snout reflex involves pursing of the lips when the area above the upper lip is tapped; the suck reflex is triggered by touching the lips or mouth. Both are associated with more advanced cognitive impairment when they appear in the context of dementia.

Not all of these reflexes carry equal weight. A lone palmomental reflex in an otherwise healthy 55-year-old is a very different finding from a grasp reflex combined with a suck reflex in someone with memory complaints. Clinicians generally become more concerned when multiple primitive reflexes appear together, when they are strong and reproducible, and when they are accompanied by other signs of neurological decline.

Primitive Reflexes in Dementia

The connection between primitive reflexes and dementia is well documented, though the relationship is more about severity than diagnosis. In both Alzheimer’s disease and vascular dementia, patients show considerably more primitive reflexes than age-matched controls, and the number of reflexes present tracks with how severe the dementia is.¹⁰ Research specifically looking at Alzheimer’s found that lower cognitive test scores correlated with having more primitive reflexes, and the snout, sucking, and grasping reflexes in particular were tied to greater impairment.¹¹

Different types of dementia show different patterns. A study comparing dementia subtypes found that people with dementia with Lewy bodies and Alzheimer’s with cardiovascular disease had more primitive reflexes than those with frontotemporal dementia, an interesting finding given that frontotemporal dementia is by definition a disease of the frontal lobes.¹² Neuroimaging research using PET scans has confirmed that specific reflexes in dementia map onto distinct areas of reduced brain metabolism, supporting the idea that each reflex is “released” by damage to a particular cortical region rather than by some generalized brain deterioration.¹³

Can primitive reflexes help diagnose dementia early? The evidence is mixed. The palmomental reflex appears with greater frequency in Alzheimer’s patients younger than 80 even two years before diagnosis, when it was present in about a quarter of those who would develop the disease versus 7% of controls.¹⁴ When the palmomental reflex was combined with a smell test in patients whose standard cognitive screening looked normal, the two tests together reached about 71% sensitivity and 64% specificity for catching dementia that other tests had missed.¹⁵ These numbers are not strong enough to use as a standalone screening tool, but they suggest that primitive reflexes still have a role as supplementary red flags, especially when they show up alongside other subtle signs.

After Traumatic Brain Injury

Primitive reflexes are not limited to the slow erosion of neurodegenerative disease. They also appear after acute brain injuries, and in that setting they tend to carry fairly direct prognostic meaning. After traumatic brain injury, the presence of frontal release signs like the glabellar, snout, suck, grasp, and palmomental reflexes predicts how well a patient will do on bedside cognitive tests, how functionally independent they will be, and how long they will need inpatient rehabilitation.¹⁶

In the acute setting, these reflexes are useful precisely because they are easy to check without equipment or patient cooperation. A person with severe brain injury may not be able to follow complex instructions for formal neuropsychological testing, but an examiner can still stroke their palm or tap above their eyebrows. The reflexes give clinicians a quick, bedside signal about the extent of frontal lobe involvement and can help guide early rehab planning.

The Problem of Reliability

For something that seems so straightforward, actually detecting and scoring primitive reflexes is surprisingly inconsistent. A study specifically designed to test whether two experienced neurologists could agree on what they found during reflex testing revealed sobering results. When the clinicians used a standard neurological exam approach, their agreement on primitive reflexes was very poor. It improved considerably only after they adopted a much more explicit, standardized protocol that separately rated how strong the reflex was and whether it persisted with repeated testing.¹⁷

This matters because many of the studies on primitive reflexes were done without such standardized approaches. The wide variation in reported prevalence rates across studies likely reflects not just genuine population differences but also differences in how hard the examiner tapped, how they defined a positive response, and how many times they repeated the stimulus. When you see one study reporting that 30% of healthy older adults have a snout reflex and another saying 5%, the gap may say as much about methodology as about the populations studied.

Reproducibility within a single examiner was better. When one investigator tested the same patients twice within two weeks using the standardized protocol, agreement was good to excellent. The take-home: primitive reflexes are a more reliable clinical tool when tested systematically, but in everyday practice, different doctors may reach different conclusions about the same patient.

Primitive Reflexes and Cognitive Decline in Healthy People

One of the more interesting open questions is whether finding primitive reflexes in a cognitively healthy adult predicts anything about their future. The Maastricht Aging Study, as mentioned earlier, found no link between reflexes and cognitive decline over six years. But the JAMA Network Open study from 2026 specifically investigated whether frontal release signs in cognitively intact research participants predicted future decline, describing these signs as markers that reappear with neurodegeneration.¹⁸ The fact that researchers are still actively studying this question in the mid-2020s tells you the evidence has not settled neatly.

Part of the difficulty is that “cognitively intact” and “healthy brain” are not quite the same thing. The study of healthy older volunteers that found primitive reflexes in half the group also found that those with small incidental brain lesions on MRI were more likely to have reflexes, even though their thinking abilities were no different from those without lesions.¹⁹ These small lesions, often called white matter changes or silent infarcts, accumulate with age and vascular risk factors. So primitive reflexes in healthy aging might be picking up early, subclinical brain changes that have not yet caused noticeable problems. Whether those changes eventually progress to something symptomatic in some people is what researchers are still trying to figure out.

Retained Primitive Reflexes as a Developmental Concept

A different framing of the same phenomenon has gained traction in some rehabilitation and developmental therapy circles. Rather than focusing on reflexes that re-emerge after brain damage, some practitioners talk about reflexes that never fully integrated during childhood and persist into adulthood. This “retained primitive reflex” framework is applied to conditions ranging from autism spectrum disorder to musculoskeletal problems.

A review published in Frontiers in Neurology found support for a relationship between retained primitive reflexes and cognitive and motor function in autism spectrum disorder, and suggested that interventions targeting reflex inhibition could produce positive changes.²⁰ On the musculoskeletal side, a recent editorial explored how incomplete primitive reflex integration might disrupt motor control and contribute to persistent joint instability, using a case of recurrent shoulder instability as an example.

It is worth being honest about the state of this evidence. The retained-reflex concept is intriguing but sits on a much thinner research base than the well-established neurology of frontal release signs. Many of the intervention studies are small, lack control groups, or rely on subjective outcome measures. The idea that doing specific reflex-integration exercises can improve adult motor control or cognitive function is plausible but far from proven. Clinicians who work within this framework tend to be occupational therapists, developmental optometrists, and certain physical therapists rather than neurologists, and the approach is not yet part of mainstream neurological practice.

When a Doctor Checks for Primitive Reflexes

Understanding the context in which these reflexes get tested can help make sense of what a result means. Neurologists do not typically test for primitive reflexes as part of a routine check-up in a young, healthy person. They pull out these tests when something else has already raised a flag: memory complaints, personality changes, movement abnormalities, or a recent brain injury.

In that clinical context, finding multiple primitive reflexes adds weight to the suspicion that something is affecting the frontal lobes. A strong grasp reflex in a 60-year-old with progressive apathy and disinhibition points toward frontal lobe involvement. A non-habituating glabellar tap in someone with a resting tremor and shuffling gait adds to the clinical picture of parkinsonism. Frontal release signs after a car accident help the rehabilitation team understand how much frontal lobe recovery to expect.

But a single primitive reflex found incidentally during a thorough neurological exam, especially a palmomental reflex or a borderline glabellar response, often means nothing at all. The high prevalence of isolated reflexes in healthy adults makes overinterpretation a real risk, and experienced clinicians know to weigh these findings against the full clinical picture rather than treating any single reflex as an alarm bell.

Why Primitive Reflexes Are Not a Blood Test

There is a temptation to treat primitive reflexes as a simple diagnostic shortcut: reflex present means disease, reflex absent means health. The reality is messier in almost every direction. Sensitivity is often moderate at best, meaning plenty of people with real brain disease will not show the reflex. Specificity is often poor, meaning many healthy people will test positive. The glabellar tap’s roughly 36% specificity for Parkinson’s disease illustrates this perfectly: two-thirds of people who do not have Parkinson’s will still show a positive result.²¹

Add in the reliability problems between different examiners, the influence of how the test is performed, and the high background rate in healthy aging, and you can see why no neurologist would diagnose a condition based on primitive reflexes alone. Their value lies in pattern recognition: they contribute to the overall clinical impression alongside history, imaging, cognitive testing, and other neurological signs. They are a piece of the puzzle, not the whole picture, and understanding that distinction matters if you or someone you care about has these reflexes tested.

Primitive Reflexes and Medications

One question that occasionally comes up is whether medications can bring out or suppress primitive reflexes. The evidence here is thin, but the Parkinson’s disease literature offers one clear data point: dopaminergic medication, the standard treatment for Parkinson’s, does not change the non-habituating glabellar tap response.²² This makes sense when you consider that the reflex is driven by structural brain changes rather than a simple neurotransmitter deficit. Drugs that boost dopamine improve motor symptoms like tremor and stiffness, but they do not restore the cortical inhibition that keeps primitive reflexes suppressed.

Certain sedating medications, heavy alcohol use, and metabolic disturbances like severe liver or kidney failure can temporarily bring out primitive reflexes by impairing cortical function. In those cases, the reflexes may fade once the underlying metabolic problem is corrected or the offending drug is stopped. This transient reappearance is yet another reason that finding a primitive reflex demands interpretation in context rather than jumping to conclusions about permanent brain damage.