The Startle Reflex: The Initial Spark of Freeze–Fight–Flight Activation

The Startle Reflex is the earliest postural motor reaction to sudden sensory input, emerging in utero between 9–12 weeks gestation. It serves as a primitive survival mechanism, activating the reticular brainstem in response to unexpected threat—auditory, tactile, vestibular, or visual. Unlike the Moro Reflex, which follows a full arc of extension and recoil, the Startle reflex is a pure flexor response, rapid, involuntary, and globally defensive.

When triggered, the response begins with a bilateral blink, followed by immediate contraction of the neck, shoulders, diaphragm, and deep core. This sequence occurs within 30–50 milliseconds, bypassing cortical processing. It is not a social or communicative reflex—it is pure brainstem defense, marking the first motor imprint of hypervigilance.

The Fear Paralysis Reflex (FPR): The Primordial Freeze Response

 The Fear Paralysis Reflex (FPR) is the earliest-appearing defensive reflex in fetal development, emerging as early as 5–8 weeks gestation. It precedes all motoric fight-or-flight responses and represents the organism's first organized reaction to threat: tonic immobility. This freeze state is characterized by stillness, bradycardia, breath-holding, and muscular tension throughout the deep core.
Unlike the Startle or Moro reflexes, which produce visible motor output, FPR is a silent, full-body inhibition. Its role is to make the fetus "invisible" in response to intrauterine or environmental threat—predator, vibration, or maternal stress. It is autonomic, vagal-dominant, and deeply subcortical, involving cranial and sacral parasympathetic regulation.

The Moro Reflex: The Core Disruptor of Gut–Brain–Body Integration

The Moro Reflex, distinct from the simpler Startle Reflex, is a higher-order primitive reflex that appears at birth and is typically integrated by 4–6 months of age. It is triggered by a sudden loss of support—as if the infant is falling—and results in a global motor response: the arms and legs shoot outward, hands open wide, then recoil in a grasping motion, often accompanied by crying. This reflex is not a mere startle—it is the first vestibular–sympathetic integration event, combining full-body motor discharge with thoracoabdominal bracing, vocalization, and diaphragmatic lock.

Freeze-Based Reflexes: The Missing Foundation in Primitive Reflex Work

Core Tendon Guard Reflex (CTG): Architectural Overview

Most primitive reflex training programs, particularly those focused on pediatrics, emphasize postural and motor pattern reflexes such as ATNR, STNR, and TLR. Yet many of my early classes omitted the most foundational layer of the reflex hierarchy: the freeze responses.

Startle, Fear Paralysis Reflex (FPR), and Core Tendon Guard Reflex (CTG) all precede the Moro reflex—not just in development, but in function. These are the body’s last line of defense against threat. I first encountered this tier of reflexes through Masgutova’s Neurosensorimotor Reflex Integration (MNRI) work for PTSD. While most pediatric and OT-based programs I have taken did not cover the freeze responses, Masgutova’s system explicitly maps them in the context of trauma and autonomic dysregulation. Dr. Karen Pryor’s neuroplasticity training also explored these reflexes in detail.

Head Righting Reflex

Head Righting Reflexes are a set of midbrain-driven postural responses that begin emerging around 2–3 months of age and remain active throughout life, albeit in a more refined and voluntary form. These reflexes govern the body’s ability to maintain head and eye alignment with the horizon—a prerequisite for balance, coordinated movement, and autonomic regulation.

They are not primitive reflexes in the traditional sense, but rather transitional postural reflexes that replace primitive patterns like TLR, ATNR, and STNR. Their presence indicates maturation of vestibular–ocular–spinal coordination and the emergence of cortical control over postural tone.  

In the last two decades—especially since COVID—we’ve seen a dramatic rise in retained Head Righting reflexes in teens and young adults. Most present with fascial rigidity from T3 upward, compromising cervical rotation, vagal tone, and in severe cases, carotid and sympathetic ganglia function. 

Tonic Labyrinthine Reflex (TLR): Foundational Flexion–Extension Drive and Gravitational Orientation

The Tonic Labyrinthine Reflex (TLR) is one of the earliest reflexes to appear in human development, emerging in utero and typically integrating by 4–6 months of age, though postural traces often persist in clients with dysregulation. It establishes the infant’s first global response to gravitational orientation, mediated not by surface contact but by vestibular input from the otolith system, which senses head position in space. When the infant’s head tilts

forward (into flexion), the body reflexively moves into total flexion; when the head tilts backward (into extension), the body extends. These total-body tone shifts form the first flexor–extensor map across the fascial and muscular systems, organizing anterior–posterior tone in both prone and supine positions.

Landau Reflex: The Postural Bridge Between Core Extension and Spatial Autonomy

The Landau Reflex emerges around 3–4 months of age and typically integrates between 12–24 months, depending on trunk tone maturity and the resolution of earlier primitive reflexes. It appears only after foundational flexor patterns—particularly the Tonic Labyrinthine Reflex (TLR), Asymmetrical Tonic Neck Reflex (ATNR), and residual Moro activity—have begun to recede. This staged emergence reflects the infant’s growing ability to sustain antigravity postural extension.

Symmetrical Tonic Neck Reflex (STNR): The Hinge of Postural Control and Vertical Integration

The Symmetrical Tonic Neck Reflex (STNR) is a developmental reflex that helps a baby organize their posture and movement. It starts to show up between 6–9 months and integrates by 9–11 months. This reflex connects the movement of the head to the movement of the arms and legs in the following way: 

• When the head bends forward (flexion), the arms bend, and the legs straighten.

• When the head bends back (extension), the arms straighten, and the legs bend.

Foot Reflexes: Primitive Patterns Govern Our Connection to Earth

The primitive reflexes of the foot form a tightly interwoven system that anchors the body’s relationship to the ground. These include the Babinski Reflex, Toe Grasp Reflex, Achilles Reflex, and Stepping Reflex—each playing a distinct role in foot–core coordination, pelvic stabilization, and upright extension. While often treated as separate entities, they operate as a developmental unit, with overlapping fascial, neurological, and energetic architectures.

Palmar Grasp Reflex: The Primitive Reach-Hold Pattern of Upper Limb Control

The Palmar Grasp Reflex is a late-appearing, higher-order reflex that emerges around 28 weeks gestation and typically integrates by 4–6 months postnatally. It is triggered when pressure is applied to the palm, producing an involuntary finger flexion. Unlike more primitive trunk-based reflexes, the palmar grasp relies on finer distal coordination and is often delayed in integration if earlier reflexes—such as the FPR, Moro, TLR, or ATNR—remain active.

This reflex is vital for early hand–mouth coordination, tactile exploration, and the development of postural tone in the upper body. As with Toe Grasp, it is replaced by volitional grasp once cortical control matures.

Toe Grasp Reflex: The Primitive Anchor of Plantar Flexion and Core Stability

The Toe Grasp Reflex appears at birth and typically integrates by 9–12 months, in parallel with foot loading, arch development, and upright postural progression. It is elicited by applying gentle pressure to the plantar pads just beneath the toes, triggering an involuntary flexion and grasping of the toes.

Academic Publishing as Extraction: The Hidden Cost of Publishing Real Science

I’ve spent the last few years researching and preparing academic articles that document a neurological, trauma-informed approach to acupuncture. This was due, in large part, to my own journey through neurogenic illness. These aren’t casual musings—they were hard-earned insights shaped by my own trauma recovery, a long term background as a toxicologist, and five years of post-graduate coursework and clinical study in reflex integration and neuroscience. All of this was confirmed in treatment rooms, backed by clinical data, and crafted with care.

Achilles Reflex: The Plantar Rebound for Push-Off and Ground Response

The Achilles Reflex is a primitive freeze-based bracing pattern localized to the posterior ankle and heel. It emerges in utero and becomes structurally active in the later stages of the Core Tendon Guard (CTG) reflex, serving as one of its five primary fascial bracing zones. This reflex activates during threat states by locking the posterior ankle into plantarflexion,
recruiting the gastrocnemius–soleus complex and transmitting tension through the Achilles tendon into the calcaneus and tibial fascial plane.

This is not the Achilles deep tendon reflex (DTR) tested in orthopedic exams. Rather, it is a sustained, fascia-dominant contraction pattern consistent with the immobilization phase of a full-body freeze response. In adult clients, it is nearly always retained alongside Moro, Babinski, or Toe Grasp reflexes, particularly in those with trauma histories, plantar rigidity, or collapsed foot posture.

Asymmetrical Tonic Neck Reflex (ATNR): The Primitive Spiral of Reach and Recoil

Asymmetrical Tonic Neck Reflex (ATNR): The Primitive Spiral of Reach and Recoil

The Asymmetrical Tonic Neck Reflex (ATNR) emerges around 18 weeks gestation and should be fully integrated by 6 months of age. Often called the “fencer’s pose,” ATNR is activated when the infant’s head turns to one side. The result is a distinct asymmetrical pattern: the limbs on the face side extend, while the limbs on the skull side flex. This creates a rotational spiral across the body, preparing for visual–motor mapping, crossing midline, and later voluntary reach.

Spinal Galant Reflex: The Lateral Arc of Trunk Escape and Pelvic Mobility

The Spinal Galant Reflex appears around 20 weeks gestation and typically integrates by 9 months of age.  This reflex is triggered when the skin along the side of the infant's back is stroked, causing the infant to curve their body towards the stimulated side. The Spinal Galant Reflex plays a crucial role in the development of coordination and flexibility in the trunk, which is important for crawling and other early movements. Additionally, this reflex is thought to assist in the birthing process by helping the baby to navigate through the birth canal.