Which of the following are examples of infant reflexes that disappear as they mature?

III Clinical Significance

74 What are primitive reflexes?

Primitive reflexes are automatisms that are usually triggered by an external stimulus. They are thought to emanate from primitive regions of the central nervous system: the spine, the inner ear labyrinths, and the brainstem. Examples are rooting, which is triggered by touching the corner of the mouth, and the asymmetrical tonic neck reflex (ATNR), which is triggered by rotating the head. Some reflexes (e.g., rooting, sucking, and grasp) have survival value. Others, such as the ATNR or the tonic labyrinthine reflex, have no obvious purpose. Placing and stepping reflexes usually disappear by 2 months. Moro and grasp reflexes and the ATNR usually disappear by 5 months.

Basic Neurological Functions

Basic neurological functions reflect the general integrity of the CNS including the presence of adaptive, healthy functioning and absence of abnormal functions.

Frontal ‘release’ signs

Certain ‘primitive’ reflexes can be released by impairment of frontal lobe function. These include the pout reflex (a pouting movement stimulated by stroking the upper lip or tapping the lips), the grasp reflex (flexion of the patient's hand around the examiner's finger despite a request ‘not to grip’) and the palmomental reflex (puckering of the ipsilateral chin in response to drawing an orange stick briskly across the thenar eminence). These reflexes should be regarded as abnormal in young adult patients, but can return with advancing age. They may accompany the behavioural abnormalities associated with the frontal lobes or their connections.

Pathological reflexes

Pathological or primitive reflexes are typically present early in development of the neurotypical infant and then disappear with maturation. They become potentially relevant to the development of dementia when they reappear during an examination for neurodegenerative disease. The most common pathological reflexes studied have been suck, snout, palmomental, glabellar, and palmar grasp. There is wide disparity of the occurrence of these reflexes among the healthy adult population [165, 166]. But heretofore there has been very little data available concerning the prevalence of pathological reflexes in adults with DS who were being evaluated for dementia. However, a recent investigation at the University of Kentucky (Harp et al., unpublished observations) has found that individual pathological reflexes did not differentiate between demented and nondemented adults with DS. Yet, in aggregate, there were a higher number of these reflexes in demented individuals with DS and they appeared stronger in response to the individual stimulus. Therefore, going forward, it appears reasonable to note how the number and strength of these reflexes correlate with other signs of dementia in DS and change over time.

53.2.8 Primitive reflexes in the elderly and in Parkinson's disease

Grasp and other primitive reflexes seen in childhood are suppressed during development but may re‐emerge in old age (Bennett et al., 1996; Schott and Rossor, 2003). Typically, PD patients have a reduced rate of eye‐blinking, resulting in a ‘reptilian stare'. Normally, the glabellar reflex habituates after 2–4 taps. Sustained glabellar reflex was observed in 10% of normal volunteers ages 65–69 years and in 37% of those aged 80 years and older (Jenkyn et al., 1985). In PD, this reflex may persist and in rare cases it may produce blepharospasm. Spontaneous blepharospasm is rare in PD but is more common in progressive supranuclear palsy cases. Repeated blinking after a tap at the bridge of the nose (Myerson's sign) is common in PD. A positive snout reflex correlates with advancing age (Koller et al., 1982). As the primitive reflexes are common in the normal elderly, their presence cannot be used as evidence of PD.

Assessment of Primitive Reflexes

The presence of all PRs during the first weeks of life is indicative of the CNS integrity. They can outlast the usual time, be absent, diminished, or increased in relation to the normal state or disappear when some compromising of the cortical integration occur by pre- or perinatal events. A normal motor development is unlikely with the PR outlasting the usual time, as their disappearance is necessary for the improvement of early voluntary motor activity in childhood.

Studies in an animal model, as those by Sherrington, in 1898, who surgically disconnected the CNS inhibition in order to observe more primitive reflex responses, are in agreement with concepts still used today to explain the outlasting of the PRs or their reappearance in humans with compromised cerebral functions. In these cases, the upper injury liberates the lower centers, more specifically the brainstem, which is the underlying structure of these connections.

Understanding the normal development of motor functions is possible only when the patterns of PRs are known, which are the precursors to those functions, since they are the best tools to early detect motor disorders in childhood, being one of the early markers for CP. This fact underscores the importance of the assessment of PRs in the newborn and infant, not only for understanding the neuropsychological development of the human being, but also for the neurologic assessment of the child, with the intent to identify possible damage to the CNS in the pre- and perinatal periods. This important semiological tool helps every professional involved in the rehabilitation of children with neurological pathology not only with respect to the prognosis, but also to the planning of more suitable treatment methods. Among these are the therapies based on the Bobath method, which inhibit the PR and stimulate more advanced stages of development.

Primitive reflex activities are closely dependent on the infant’s physiological needs upon stimulation and interact with one another, at times facilitating and at other times inhibiting, as can be observed at the moment of hunger when oral reflexes have already been exacerbated, and an increase in the palmar grasp reflex and movements of general flexion of the body concomitantly occur, associated with a diminution of extensor reflexes such as the Moro, plantar support, and crossed extensor. The elicitation of the palmar grasp reflex normally inhibits the Moro reflex, which can make the infant calm down, while conversely labyrinthine stimuli and/or sudden stimuli in general elicit crying and an unstable attitude which is well characterized in the extensor phase of the Moro reflex; even in this situation the lower limbs tend to a flexor predominance and exacerbation of the plantar grasp reflex.

The techniques of examination of some PRs already had been indicated together with the description of the same ones, and in the diagrams of figures in the item of the classification of reflex.

Primitive Reflexes

A variety of primitive reflexes, some of which can be elicited in the preterm infant, are present for relatively short periods of time after birth, and these mass movements are replaced by volitional, more refined movements (Table 2). The Moro reflex is elicited in the supine infant by raising the infant's head from the bed or examining table to an angle of approximately 30–45° and then suddenly dropping the infant's head while the examiner's hand cushions the head from abruptly hitting the cot surface. The reflex consists of the infant opening the hands with arm extension and abduction, followed by anterior flexion of the arms and sometimes associated with a brief audible cry. The Moro reflex should normally disappear by 3 or 4 months of age; however, if the reflex is notably asymmetric or if there is abduction and extension of one arm only, one should consider the possibility that the infant has hemiplegia, brachial plexus palsy, or a clavicular or humeral fracture on the contralateral side.

Table 2. Primitive (postural) reflexes

The palmar grasp reflex is present at 28 weeks of gestation and becomes more forceful at 32–37 weeks. It becomes less apparent and then disappears after approximately 2 months of age, when voluntary grasping becomes apparent.

The rooting reflex is well established by 32 weeks of gestation and can be elicited by tactile stimulation of the perioral region. If the superior or inferior midline lip is stroked, the infant will move his or her mouth in the direction of that stimulus. This is also true if either the right or the left lateral aspects of the lips are stroked. The infant will follow this tactile stimulus as if in search of the nipple. This reflex is present in the full-term newborn, but it may be difficult to elicit unless it is done so at approximately the normal feeding time of the infant.

The tonic neck reflex is elicited by the rotation of the head of a supine infant to one side followed by extension of the upper limb on the side to which the head is rotated, with associated flexion on the side ipsilateral to the occiput. The reflex is usually rudimentary in normal infants and disappears by 2 or 3 months of age. The reflex is exaggerated in infants who have a static encephalopathy or in those who have sustained some cerebral insult.

The placing and stepping reflex can be elicited by approximately 37 weeks of gestation. It can be provoked by placing the anterior tibia or dorsum of the infant's foot under or against the edge of a table. The infant lifts the leg onto the table, and when holding the infant upright over the table so that the sole presses the table, there is reciprocal flexion and extension of the legs, simulating walking. The reflex disappears in normal infants by approximately 6 weeks of age.

When the normal infant is maintained in ventral suspension by the examiner's hand supporting the infant's abdomen, the head, spine, and legs extend. If the head is pushed downward, the hips, knees, and elbows flex. This Landau reflex is normally present from approximately 3 months of age and becomes increasingly difficult to elicit by 6–12 months. The absence of this reflex in infants older than 3 months is observed in those infants who have a static encephalopathy or motor weakness.

The parachute reflex appears at approximately 6–9 months of age and persists throughout life. To demonstrate its presence, the infant should be held in ventral suspension by supporting the infant under the arms and then suddenly lowering the infant to a bed or table. Normally, the arms extend as if to protect from falling. Infants who have static encephalopathy may demonstrate an asymmetric or absent parachute reflex. The reflex can also be demonstrated by propping the infant in a seated position and if the child feels unstable in this position, the arms will extend on to the appropriate side to prevent falling.

Neonatal Reflexes.

The neonatal or primitive reflexes frequently tested during routine examination of the newborn include the Moro reflex, the asymmetric tonic neck reflex, truncal incurvation (Galant reflex), the palmar and plantar grasp reflexes, the Babinski reflex, and the placing and stepping reflexes.

The Moro reflex can be elicited following the pull-to-sit maneuver, by the lowering of the newborn until there is only a slight space between the neck and bed, and then allowing the newborn to fall back suddenly. Alternatively, the Moro reflex can be elicited by the “drop” method: the examiner lifts the baby completely off the bed, supporting the head and trunk with both hands and keeping the baby supine, and then rapidly lowers the baby by approximately 4–8 inches. The complete Moro reflex involves a quick bilateral abduction of the arms and extension of the forearms with full opening of the hands, followed by smoother and slower return of the hands toward the midline, with curling of the fingers.

The startle reflex is similar to the Moro reflex, but without full extension or hand opening, and may occur spontaneously or may be evoked by a sudden noise or movement.

The asymmetric tonic neck reflex demonstrates how neck position affects the tone of the extremities. This should be kept in mind during observation of the newborn's spontaneous movements, because it can cause a false impression of asymmetry if the position of the neck is not taken into account. To test the asymmetric tonic neck reflex, turn the newborn's head 90 degrees to one side for 15 seconds, keeping the newborn lying on the back with the shoulders horizontal. In a complete response, the ipsilateral arm and leg will extend and the contralateral arm and leg will flex, producing the “fencing” posture. The test is then repeated with the head turned to the other side. Observation of the complete response is reassuring, but its absence is not necessarily abnormal (partial and unidirectional responses are common too). However, an unusually sustained or exaggerated response is abnormal.

The truncal incurvation reflex is elicited with the newborn held in ventral suspension by the examiner stroking lightly down the back on one side and then the other. The normal response is for the newborn to curve the spine strongly, concave toward the stimulated side.

The supporting, placing, and stepping reflexes are elicited with the newborn held upright. The supporting reaction is elicited by the examiner lowering the newborn vertically until both feet touch the surface of the bed or table. A positive response, usually seen after a slight delay, is partial extension at the hips and knees, as though the newborn is attempting to stand and support his or her weight. The stepping reaction is tested by the examiner lowering the newborn so that one foot touches the surface, with the newborn tilted slightly forward. The newborn should flex that leg and extend the other, as though taking a step. The placing reaction is elicited by the examiner lifting the newborn to bring the dorsum of one foot in contact with the underside of a table or bassinet edge. In a positive response, the newborn lifts the foot up and places it on the top surface.

The Babinski reflex consists of dorsal flexion of the big toe and spreading of the other toes in response to stroking of the foot laterally (normally observed in newborns).

Firm pressure on the sole of the foot elicits the plantar reflex.

The deep tendon reflexes are usually not elicited during routine examination of the well newborn, but they are helpful as part of a more complete examination if neurologic abnormalities are suspected. The pectoralis, biceps, brachioradialis, thigh adductor, crossed adductor, knee jerk, and ankle jerk reflexes are the most readily elicited (Volpe, 2008). Ankle clonus may be elicited by quick dorsiflexion of the foot, which in a healthy term newborn should produce no more than approximately five beats of alternating extension and flexion with rapidly decaying intensity.