Primitive reflexes are involuntary motor responses originating in the brainstem. These reflexes are present at birth to aid in survival, movement, and the development of higher brain function. The Moro reflex, frequently called the “startle” reflex, is one of the earliest and most well-known of these patterns. For typical neurological development to proceed, this reflex must integrate within the first few months of life, as its continued presence later in life is considered atypical.
The Moro Reflex: A Primer
The Moro reflex is a protective, involuntary motor response to a sudden change in sensory input, such as a loud noise, bright light, or the sensation of falling. When triggered in an infant, the response occurs in two distinct phases. First, the arms and legs quickly extend outward away from the body in an abduction movement. This is immediately followed by the arms retracting back toward the body in an adduction movement, often with the infant crying.
This reflexive pattern is considered an innate survival mechanism, activating the baby’s vestibular system to detect changes in balance and signaling the brainstem to initiate a “fight or flight” response. The reflex is typically present in full-term infants and should begin to integrate around two to four months of age, generally disappearing completely by six months. As the central nervous system matures, the Moro reflex is replaced by the more coordinated, voluntary adult startle reflex.
Clinical Assessment in Adults
Testing for a retained Moro reflex in an adult differs from testing in a baby, as a full infant response is not expected. Clinicians instead look for subtle, involuntary muscle tension and compensatory movements. The assessment aims to indirectly trigger the underlying reflex pattern, which is a vestige of the body’s hyper-arousal mechanism. One common method involves postural response tests that challenge the adult’s balance and vestibular system.
A professional may ask the patient to stand with their feet together and eyes closed, then observe them while they tilt their head backward. Excessive swaying, loss of balance, or involuntary tension can suggest a retained reflex. Another approach is the startle sensitivity test, where the clinician observes the individual’s reaction to an unexpected, loud auditory stimulus.
The clinician looks for a disproportionately large physical reaction or an exaggerated jump, where the arms may briefly flail or the torso may jolt. Professionals also observe the immediate psychological and emotional response, such as a strong feeling of agitation or a lingering sense of being jolted. Specialized practitioners use a grading system to determine if the reflex is fully integrated, partially retained, or strongly retained based on the intensity of the observed involuntary reaction.
Manifestations of Retention
When the Moro reflex does not fully integrate, the nervous system remains in a perpetual state of hyper-arousal, leaving the individual stuck in an underlying “fight or flight” mode. This state causes the adult to constantly misinterpret low-level sensory input as a threat, leading to chronic anxiety and an exaggerated stress response. The individual may experience panic attacks or a constant feeling of being “on edge.”
A retained Moro reflex is strongly linked to hypersensitivity across multiple sensory domains. Affected individuals often report being overwhelmed by environments with bright lighting, loud noises, or unexpected touch. Because the nervous system constantly reacts to stimuli, it struggles to filter out irrelevant information, leading to chronic distractibility and attention issues.
This neurological overload also impacts emotional regulation, resulting in increased irritability, mood swings, and difficulty adapting to sudden changes in routine or environment. Physical manifestations include motion sickness, poor balance, and general physical timidity. The constant, subconscious effort required to suppress the active reflex also contributes to chronic fatigue.
Addressing Retention
Retained reflexes can be the result of factors that disrupted the normal developmental process, such as birth trauma, chronic illness in infancy, or a lack of sufficient movement opportunities like tummy time. The therapeutic approach involves Primitive Reflex Integration Therapy. This therapy uses specific, targeted, movement-based exercises designed to mimic the natural developmental motions that should have inhibited the reflex in infancy.
These exercises, often inspired by methods like Rhythmic Movement Training, are performed gently and repetitively to create new neural pathways that bypass the reflex. For example, exercises like the “Starfish” or “Popcorn” involve alternating between a flexed, curled-up position and a rapid extension, which helps the nervous system gain voluntary control over the pattern. The goal is to fully integrate the reflex at the brainstem level, reducing the chronic state of hyper-arousal and alleviating associated physical and emotional symptoms.