The plantar grasp reflex is of great clinical significance, especially in terms of the detection of spasticity. The palmar grasp reflex also has diagnostic significance. This grasp reflex of the hands and feet is mediated by a spinal reflex mechanism, which appears to be under the regulatory control of nonprimary motor areas through the spinal interneurons. This reflex in human infants can be regarded as a rudiment of phylogenetic function. The absence of the Moro reflex during the neonatal period and early infancy is highly diagnostic, indicating a variety of compromised conditions. The center of the reflex is probably in the lower region of the pons to the medulla. The phylogenetic meaning of the reflex remains unclear. However, the hierarchical interrelation among these primitive reflexes seems to be essential for the arboreal life of monkey newborns, and the possible role of the Moro reflex in these newborns was discussed in relation to the interrelationship.
Both the palmar grasp reflex and the plantar grasp reflex are very primitive in the sense that they can be elicited in all normal preterm infants at as early as 25 weeks of postconceptional age (PCA) [
The Moro reflex was first described by Ernst Moro in 1918 [
It is interesting that, in spite of the great difference in the motor behavior, there is a close interrelationship between these primitive reflexes in the responses: the palmar grasp reflex inhibits the Moro reflex [
To elicit the palmar grasp reflex, the examiner inserts his or her index finger into the palm of the infant from the ulnar side and applies light pressure to the palm, with the infant lying on a flat surface in the symmetrical supine position while awake [
The plantar grasp reflex is elicited by pressing a thumb against the sole of a foot just behind the toes [
The grasp reflexes of the hands and feet in normal term infants have been studied by several authors. Their results were fairly consistent regarding the times of the appearance and disappearance of the reflexes. The palmar grasp reflex and the plantar grasp reflex can be elicited in all infants during the first 3 and 6 months of age, respectively. Thereafter they decrease along with the intensity of the responses, usually disappearing by 6 and 12 months of age, respectively [
In contrast to the studies involving term infants, those involving preterm infants have been few. Allen and Capute [
In general, a primitive reflex in infants is regarded as abnormal when it is absent or diminished during the period it should be actively elicitable or lasts beyond the normal age limit for its disappearance. An exaggerated reflex can also be abnormal. The response of the palmar grasp reflex may be less intense during the first and second days after birth [
The clinical value of the plantar grasp reflex in infants has been investigated in more detail than that of the palmar grasp reflex. In 1932, Brain and Curran [
A reduced or negative plantar grasp reflex during early infancy can be a sensitive indicator of later development of spasticity. Of 2267 infants whose plantar grasp reflex had been examined before 1 year of age, we analyzed the neurodevelopmental outcome in 47 infants exhibiting a negative response during the first 6 months of age and in 46 infants exhibiting a significantly reduced response at ages 1 to 4 months [
A high concordance between the side of an abnormal plantar grasp reflex during infancy and the laterality of the disturbance of motor function in children with CP of the spastic type was demonstrated [
Because anencephalic infants demonstrate a positive grasp reflex in both the hands and feet, the cerebral hemispheres are apparently not necessary for the reflexes [
The spinal reflex center, however, is controlled by a higher brain mechanism. The grasp reflexes can be elicited in neonates and early infants as a result of insufficient control of the spinal mechanism by the immature brain, but the reflexes gradually disappear with age, due to the increased inhibition accompanying brain maturation [
Many attempts have been made to determine the pathological site of the grasp reflexes by means of clinical observation or animal experiments [
Nonprimary motor areas play important roles in the planning, preparation, initiation, and execution of motor behavior [
However, the proportion of patients with a lesion of a nonprimary motor area in whom a grasp reflex can be elicited is not necessarily high. In the series of De Renzi and Barbieri [
Clinical studies have revealed that some patients with a frontal lesion exhibit a grasp reflex of the hands or feet, or both [
In normal circumstances, higher brain centers control the spinal mechanism that regulates the coordination among agonists, antagonists, and synergists in an adaptable manner by means of reciprocal innervation. In children with spastic type CP, however, deviation in terms of reciprocal innervation caused by damage to the pyramidal tract leads to excess cocontraction at proximal joints, whereas deviation leads to excess reciprocal inhibition through spastic antagonists at distal joints, inducing weakness of the agonists [
On the other hand, in children with CP of the athetoid type, the deviation of reciprocal innervation always leads to excess reciprocal inhibition. Any attempt at movement produces excessive relaxation of the antagonists, inducing an extreme range of movements [
In infants, the maturation of cortical connections overrides the generators of primitive reflexes in the spinal cord and brain stem with age and eventually leads to the disappearance of the primitive reflexes and the emergence of righting and equilibrium reactions [
In his original method, Moro [
The drop of the baby method is an alternative one for eliciting the reflex: the infant is suspended horizontally, as in the head drop method, and then the examiner lowers his or her hands rapidly about 10 to 20 cm and brings them to an abrupt halt. There is no dorsiflexion of the neck with this technique [
The initial phase of the response comprises abduction of the upper limbs at the shoulders and extension of the forearms at the elbows, with slight extension of the spine and retraction of the head. The forearms are supinated and the digits extended, except for the semiflexed index fingers and thumbs, forming the shape of a “C”. There is sometimes a slight tremor or clonus-like rhythmic movements of the limbs. Subsequently the arms adduct at the shoulders and the forearms flex at the elbows: the upper limbs describe an arc-like movement, bringing the hands in front of the body, which finally return to the original position [
The study of the Moro reflex in normal term infants has been undertaken by many authors. The results obtained with the head drop method are well consistent. The reflex can be elicited in all infants during the first 12 weeks of age. After the neonatal period, however, the response becomes increasingly less typical with age, eventually consisting only of abduction and extension of the upper limbs. Beyond 12 weeks of age, the proportion of infants exhibiting a negative response rapidly increases, reaching about 80% at 20 weeks of age [
Based on the findings in normal infants, the absence or diminution of the Moro reflex within 2 to 3 months of age and the persistence of the response beyond 6 months of age can be regarded as abnormal. The absence of the response during the neonatal period and early infancy is of especial clinical significance and may indicate a compromised condition or disorder including birth injury, severe birth asphyxia, intracranial hemorrhage, infection, brain malformation, general muscular weakness of any cause, and CP of the spastic type [
Asymmetry of the response is usually a sign of local injury. Damage to a peripheral nerve or cervical cord or a fracture of the clavicle may inhibit the reflex on the affected side. However, it should be noted that Dubowitz [
Katona [
The origin of afferent pathways for the Moro reflex, whether it is primarily vestibular, proprioceptive, or exteroceptive, has been a main subject of discussion. The head drop, the most common way of eliciting the reflex, stimulates both the vestibular system and the proprioceptive receptors in the neck. Rönnqvist [
On the other hand, Parmelee Jr. [
Although pinching of an infant’s epigastrium has been reported to be effective for eliciting the reflex [
The reflex center probably contains a number of interneurons, because of the relatively long latency. The routes of afferent pathways can be multiple, and the efferent pathways of the response seem to originate in the vestibulospinal and/or reticulospinal neurons, because the response can even be obtained in anencephalic newborns devoid of both corticospinal and rubrospinal neurons [
Although there has been much confusion regarding the Moro response and the startle reaction in the past, most authors agree today that they are different entities [
In 1891, Robinson [
Based on these findings, the grasp reflex of the hands and feet in human infants could be regarded as a rudiment of phylogenetic functions that were once essential for monkey infants in arboreal life and that have lost their usefulness in the human species [
In his original paper, Moro [
Several authors observed in human newborns that the palmar grasp reflex inhibits the Moro reflex [
Based on the findings already mentioned in this paper, the Moro reflex in the young monkey would be elicited when the vestibular system is stimulated with abrupt tilting of the body or head while it is being passively held by its mother without active clinging caused by the palmar grasp reflex. In this situation, the mother would notice her baby was off balance from its exaggerated reflex movement, and she would immediately try to seize the baby to prevent a fall. It might be possible to assume that the Moro reflex in monkey neonates plays a role in such interaction between mother and child for protection against a fall. To clarify the meaning of the Moro reflex, it appears necessary to determine in monkeys in what situation the reflex is elicited and how the response works in the mother and child.
The palmar grasp reflex in infants has diagnostic significance. The absence or a weak response of the reflex during early infancy may reflect peripheral nerve or spinal cord involvement or may predict the development of athetoid type CP, whereas the response may be hyperactive in children with spasticity in their upper limbs. The plantar grasp reflex is also of high clinical significance, especially in terms of the detection of spasticity. No reflex, or a diminished one, during early infancy is often a sensitive predictor of the development of spastic CP. The grasp reflex of the hands and feet is mediated by the spinal reflex mechanism, which, however, appears to be under regulatory control of nonprimary motor areas through the spinal interneurons. The absence of the Moro reflex during the neonatal period and early infancy is highly diagnostic, indicating a variety of compromised conditions. The center of the reflex is probably in the lower region of the pons to the medulla. The grasp reflex of the hands and feet in human infants could be regarded as a rudiment of phylogenetic function, whereas the phylogenetic meaning of the Moro reflex remains unclear. The hierarchical interrelations among the primitive reflexes seem to be essential for monkey newborns for their arboreal life, although it has not been fully elucidated. The possible role of the Moro reflex in these newborns was discussed in relation to the interrelations.