WHAT ARE THE PRIMITIVE REFLEXES OF THE NEWBORN? - NEUROPSYCHOLOGY - 2024

The primitive reflexes of the newborn are the reflexes that neonates perform involuntarily. In the medical literature, in addition to primitive reflex, a great variety of terms have also been used: primary neonatal reflexes, developmental reflexes, infantile reflexes and reactions or automatisms (García-Alix & Quero, 2012).

Some movements are spontaneous, occurring as part of the baby's usual behavioral repertoire. On the other hand, reflexes also occur in response to certain stimuli (University of Rochester Medical Center, 2016).

Reflexes are one of the essential components in physical and neurological examinations, since their abnormal presentation or absence can be an indicator of a possible compromise in the nervous system (University of Rochester Medical Center, 2016).

On the other hand, we must bear in mind that some reflexes have a transient component, some types will only appear in specific periods of child development (University of Rochester Medical Center, 2016).

What are primitive reflexes?

With the term primitive reflex we refer to a set of highly stereotyped motor responses triggered spontaneously or to specific stimuli that are part of the normal motor behavior of babies (García-Alix & Quero, 2012).

Most of these motor responses appear during the second half of the gestation period and will be present in the postnatal stage (García-Alix and Quero, 2012).

All the variety of involuntary movements will allow the baby to: develop the motor system, descend through the birth canal or suck to feed, among other functions (BRMT, 2016).

However, some of them will disappear following a pre-established order during the first year of life (García-Alix and Quero, 2012).

Reflexes are part of the newborn's later motor development and, therefore, their evaluation is part of the neonatal neurological examination. This allows us to assess the general development of the nervous system (García-Alix and Quero, 2012).

When there is some type of deficit at the neurological level, it is possible that some of the primitive reflexes remain active during late stages of development, and will hinder the acquisition of motor skills as well as sensory perception and cognitive development (BRMT, 2016).

When do reflections appear?

Already during the prenatal stage, evidence of primitive reflex activity can be observed (Carlson, 2000; Roselli and Matute, 2010).

Specifically, around the sixth week of gestation, touching the skin around the mouth can cause a contralateral flexion of the neck (Roselli and Matute, 2010).

Between the sixth and eighth week of gestation, reflex responses can be observed when stimulating the skin of the upper chest area, the palms of the hands or the face (Roselli and Matute, 2010).

In the case of the twelfth week of gestation, approximately the entire body surface is sensitive, except for the back or crown. Consequently, the reflex responses become more specific (Roselli and Matute, 2010).

Types of reflexes in the newborn or neonate

Primitive reflexes can be divided into two large groups: primitive postural reflexes and primitive tactile reflexes (García-Alix and Quero, 2012):

• Primitive postural reflexes: they are produced as a consequence of the stimulation of the receptors of the vestibular apparatus by the movement of the head - Moorish reflex. At the neurobiological level, they are mediated at the level of the brainstem.
• Primitive tactile reflexes: they occur as a consequence of tactile stimulation, plantar response, Galant reflex, grasp reflex, etc.). At the neurobiological level, they are mediated at the level of the spinal cord.

Postural reflexes

The most relevant postural reflexes are: Moro reflex, asymmetric tonic cervical reflex and the labyrinthine tonic reflex. Everything except the Moro reflex is characterized by developing with variable and incomplete responses.

This type of postural reflex is only observed during postnatal life, because a suppression occurs during the gestation period so that the fetus does not respond to every movement made by the mother.

- Reflection of Moro

The moro reflex or startle reflex occurs when the baby is startled by a loud sound or movement. In response, the baby moves her head back, extends her arms and legs (University of Rochester Medical Center, 2016).

The Moro reflex can be triggered as a consequence of several stimuli: sudden sound or a sudden movement of the surface where the baby is placed, among some others (García-Alix and Quero, 2012)

When any of the above stimuli appear, a complete opening of the hands occurs in the baby, followed by a flexion of the fingers (forming a 'C' between the thumb and the index finger) (García-Alix and Quero, 2012)

The Moorish reflex has several phases (García-Alix and Quero, 2012):

• First phase: extension of the forearms.
• Second phase: adduction of the arms and flexion of the forearms.
• Final phase: crying or grimacing with anxiety.

- Asymmetric tonic cervical reflex

The asymmetric tonic cervical reflex occurs when the baby is relaxed and lying down and turns the head to one side. The arm on the side towards which the head is positioned is extended away from the body with the open hand and the arm on the opposite side is flexed (National Institutes of Health, 2013).

If the baby turns his head to the contralateral side, the movement pattern is reversed (National Institutes of Health, 2013).

-Labyrinthine tonic reflex

When the baby is in the supine position (the baby is lying on the back on his back with the limbs extended), the extension of the head produces a retraction of the shoulders and extension of the legs (García-Alix and Quero, 2012).

In the prone position (the baby is lying face down with the head on the side), the flexion of the head produces a flexion of the legs (García-Alix and Quero, 2012).

Tactile reflexes

Tactile or cutaneous reflexes are produced as a result of stimulation of the skin in a specific area. This stimulation triggers a motor response that takes place in the same place where the stimulation was applied.

The most important tactile reflexes are: sucking reflex, searching or sniffing reflex, Galant reflex or trunk invurvation, Vollmer reflex and Perez reflex, cross extension reflex, magnet reflex or magnetic reflex, step reflex, automatic gait reflex, positive support reflex (palar pressure, finger extensor, babinski reflex, plantar response).

- Suction reflex

When tactile stimulation of the baby's upper palate or tongue is performed, it begins to suck (University of Rochester Medical Center, 2016).

The sucking reflex has a main role in survival, since it is essential for the feeding of the newborn (García-Alix and Quero, 2012).

- Search reflex or sniff

When the corner of the mouth or the cheek is stimulated on the surface of the face on one side and then on the other, the child responds by moving the lips and tongue towards the location of the tactile stimulus (García-Alix and Quero, 2012).

- Reflection of Galant

The Galant reflex or trunk bend occurs when the skin along the baby's spine is stimulated while the baby is on his tummy (National Institutes of Health, 2013).

Specifically, this reflex can be produced by brushing the skin on both sides of the spine with the index finger, from the shoulder to the buttocks. tactile (García-Alix and Quero, 2012).

Automatically, after stimulation, the baby curves the spinal column towards the side where the stimulation is taking place (García-Alix and Quero, 2012).

- Reflection of Vollmer and reflection of Pérez

In the Vollmer reflex, when firm pressure is applied along the spine, there is a flexion of the arms and legs with a dorsal extension of the spine and neck (García-Alix & Quero, 2012).

In the Pérez reflex, when firm pressure is applied along the cervico-thoracic spine, there is a flexion of the arms and legs with a dorsal extension of the lower spine (García-Alix & Quero, 2012).

- Cross extension reflex

In the crossed extension reflex, when tactile stimulation is applied to the sole of the foot while keeping the extremity to which it is to be applied is extended, it results in a response composed of three phases (García-Alix and Quero, 2012):

• First phase: spontaneous flexion of the leg that is free.
• Second phase: extension or opening of the toes of the foot on which the stimulation has been performed.
• Third phase: extension and adduction of the free foot towards the stimulated one.

- Magnet reflection or magnetic reflection

When the baby is lying on his back and light pressure is applied with the thumb on the soles of both feet, the baby extends his legs to maintain contact (García-Alix and Quero, 2012).

- Step reflex

The step or positioning reflex occurs when the baby is in an upright position held below the armpits (García-Alix and Quero, 2012).

When stimulation is applied under the dorsum of the foot, the baby responds by raising the foot and placing it on the surface, through a knee and hip flexion with an extension of the foot (García-Alix and Quero, 2012).

- Automatic gear reflex

The automatic gait reflex occurs when the baby is placed in an upright position, placing his feet on a surface (García-Alix and Quero, 2012).

The baby, in this position, responds by straightening the lower limbs and trunk, and performing a succession of steps, synchronizing the flexion of the hip with that of the knees (García-Alix and Quero, 2012).

- Palmar pressure reflex, finger extensor, babinski reflex, plantar response

The surface of the skin of the palm of the hand and the sole of the foot, with one of the skin areas of the body most sensitive to stimulation, so there are several primitive reflexes associated with these:

• Palmar pressure reflex: when we put a finger on the palm of a newborn's hand, it reacts by closing it around the finger. If an attempt is made to withdraw, the neonate squeezes his fingers, exerting force against the tactile stimulus (National Institutes of Health, 2013).
• Extensor finger reflex or digital response: an opening of the fingers of the hand occurs when the surface of the little finger or the back of the hand is repeatedly stimulated (García-Alix & Quero, 2012).
• Babinski reflex: When the surface of the sole of the foot is stroked, the toes fan out (National Institutes of Health, 2013).
• Plantar response: when an intense tactile stimulus is applied to the lateral area of ​​the sole of the foot, from the heel to the thumb, an extensor response is produced in the thumb (García-Alix & Quero, 2012).

What is the temporal evolution of primitive reflexes?

• Moro reflex: it appears well established around week 37 of gestation and disappears approximately between 5-6 months of age.
• Asymmetric tonic cervical reflex: It appears well established around 1-2 months of age and disappears between approximately 6 and 9 months of age.
• Suction reflex: it is well established between weeks 34 and 36 of gestation and disappears at 4 months of age.
• Search reflex: it is well established between weeks 34 and 36 of gestation and disappears after 4 months of age.
• Palmar pressure reflex: it appears well established around week 32 of gestation and disappears between 6 and 9 months of age.
• Galant's reflex: it is present and well established around week 32 of gestation and disappears between the first and second year of life.
• Labyrinthine tonic reflex: it is present approximately between 2 and 4 months of age and disappears between 11 and 24 months of the postnatal stage.
• Localization reflex: it is present and well established around the 40th week of gestation and disappears between the first and second month of life.
• Gait reflex: it is present and well established around week 40 of gestation and disappears between the first and second month of life.
• Extension reflex: it is present and well established around the 40th week of gestation and disappears between the first and third month of life.

Why are reflexes tested in newborns?

As we have pointed out in other sections, there are several reasons to carry out an analysis of primitive reflexes in newborns (García-Alix and Quero, 2012):

• They help us assess the general development of the baby's nervous system.
• They allow us to assess the specific integrity of the central nervous system (CNS).
• In some cases, they may have localization value and therefore help us to identify the possible site of an injury or structural damage.

References

1. BCA. (2013). Infant Reflexes. Obtained from Baby Care Advice: babycareadvice.com
2. García-Alix, A., & Quero, J. (2012). Primitive or developmental reflexes. In A. García-Alix, & J. Quero, Primitive or developmental reflections.
3. Nall, R. (2014). What Are Neonatal Reflexes. Obtained from Healthlilne: healthline.com
4. NIH. (2013). Infant Reflex. Retrieved from MedlinePlus:
5. Roselli, M., & Matute, E. (2010). Cognitive and brain development. In N. d. infantil, Roselli, M.; Matute, E.; Ardila, A.;.
6. UR. (2016). Newborn Reflexes. Retrieved from Univesity of Rochester Medical Center: urmc.rochester.edu