Why Does Replicating a Primitive Reflex Inhibit the Reflex?

The replication of primitive reflexes is growing in evidence. It has been used effectively in several intervention and laboratory studies in children and adults. At first glance, this is in conflict to various therapies that use normal movement such as the Bobath or NDT approach.

First it is important to understand the difference between the "replication" and the "reproduction" of the primitive reflex (PR).

Replication of the Primitive Reflex

(1) Where appropriate, the sensory stimulus is slowly and passively replicated.

(2) The movement pattern of the PR is cognitively and actively replicated. There is no automatic response of the reflex

Reproduction of the Primitive Reflex

During either the stimulation of the sensory reflex or during the replication of the movement pattern, there is an unconscious reproduction of the primitive reflex. This is non therapeutic and can be harmful to the motor control pattern. It happens more often with reflexes that have a tactile sensory stimulus, during the stimulation of the tactile stimulus (e.g. Babinski, Foot Tendon Guard, Sucking Reflexes). Note: in neurological patients, the reproduction of the PR is frequently seen during functional movements or while using normal movement or postural responses to inhibit the reflex.

These observations likely have contributed to the misconceptions of PR Replication to inhibit the reflexes. It is critical to the therapeutic effect that the PR is not reproduced replicated while it is cognitively being replicated.

The Neurodevelopmental Process

There is a belief that the neurodevelopmental process is a sequential development:

Primitive Reflexes » Sensory Motor » Postural Reflexes » Goal Orientated Movement

Although this is a nice way to explain the process in textbooks, development doesn't occur as simple as this. Development uses each of these processes to "feed off" of each other.  In general terms it could be said that in early development the former may be more dominant (primitive reflexes and sensory motor) and in later development the latter may be more dominant (postural reflexes and goal orientated movement).

For example, an infant is prone and hears a sound. This auditory stimulus  (sensory) facilitates an extensor response and the head and trunk move into extension (primitive reflex). When the head is up (and during) oculomotor is used (sensory) and the vestibular system and kinesthetic system (sensory) is stimulated. The infant may then decide to move (goal orientated movement).  If it is a roll (postural reflex, but can be primitive depending on the time frame), there is lower limb, upper limb and neck "coordination", the vestibular system and kinesthetic systems are stimulated (sensory) and the tactility system is stimulated (sensory).

In gross terms, as the neurodevelopmental process and primitive reflexes are going through their normal developmental timeframe, higher cognitive centers (frontal lobe) are facilitated. The appreciation of this neurodevelopmental principle has helped us understand and develop a hypothesis of why the replication of PR helps inhibit the PR. 

We have now observed three cases in infants which have helped develop and support our hypothesis that it is the cognitive and active replication of the reflex which inhibits the PR.This in turn facilitates specific higher centers which then inhibit the reflex.

The observations were:

1.    In the same setting the infant's reflexes were checked and the infant had a grasp reflex

2.    The infant made a conscious decision to reach for a toy and grasped it fully and then brought it back to their body

3.    The infant's primitive reflex was absent immediately following the activity of making a cognitive decision to reach for the object and achieve the goal of grasping it and bringing it back to their body.

In infants or in adults it may be possible that passively replicating the PR can also have a clinical benefit. This may be through the mirror neuron system. If our hypothesis is correct, we need to take advantage of the cognitive aspect of the process during our clinical application of PR inhibition.

Although we need further clarification and understanding of the central mechanisms, these cases and hypothesis provide a plausible hypothesis to pursue. 

Sean GT Gibbons BSc (Hons) PT, MSc Ergonomics, PhD (c), MCPA

References

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