Palmar grasp reflex (or grasp reflex) is a primitive and involuntary reflex found in infants of humans and most primates. When an object, such as an adult finger, is placed in an infant's palm, the infant's fingers reflexively grasp the object. Placement of the object triggers a spinal reflex, resulting from stimulation of tendons in the palm, that gets transmitted through

motor neurons A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly ...

in the median and ulnar sensory nerves. The reverse motion can be induced by stroking the back or side of the hand. A

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...

exhibits the reflex ''in utero'' by 28 weeks into gestation (sometimes, as early as 16 weeks), and persists until development of rudimentary fine motor skills between two to six months of age.

Evolutionary significance

Biologists have found that the reflex is significantly more frequent in infants of fur carrying primate species. It is theorized that the grasping reflex evolved as it is essential to survival in species, usually primates, where the young are carried in the fur. The infant's ability to grasp onto a mother's fur allows the mother to keep the infant with her while foraging for food or moving from one place to another. This is beneficial to the mother because she does not lose function of her limbs or mouth (as she would from oral carrying). Carrying the infant with the mother also gives a degree of safety to the infant, which it would not have if it were left in a nest or other location away from the mother. The grasp reflex also allows young individuals to have more developed food manipulation and dexterity skills. This suggests that the grasping reflex is

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

in humans and in other non-fur carrying primates. The reflex is also suggested to create a basis for which the voluntary grasping action originates. This comes from the maturation of higher motor centers, allowing a child to exert more control over the body.

Clinical significance

In humans, absence of the palmar grasp reflex or persistence of the reflex can both be indicators of neurodevelopmental abnormalities. In a normal infant, the palmar grasp reflex is present during the first three months of age and disappears by six months of age. Disappearance of the reflex has been attributed to conscious and voluntary hand use. Based on collected evidence, there is no significant difference between the reflexes of normal-term and pre-term infants. Absence of the grasp reflex could indicate a neural communication error with the spinal cord. In other words, signals from the stimulation of tendons in the palm are being interrupted before they have a chance to make it to the spinal cord, resulting in a lack of the reflex. Absence of the grasp reflex could also be an indicator of

peripheral nerve injury Nerve injury is an injury to nervous tissue. There is no single classification system that can describe all the many variations of nerve injuries. In 1941, Seddon introduced a classification of nerve injuries based on three main types of nerve f ...

or injury to the spinal cord. Persistence of the grasp reflex could be an indication of brain

lesions A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...

cerebral palsy Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, stiff muscles, weak muscles, and tremors. There may be problems with sens ...

. Presence of the reflex in infants older than four months could be an indicator of damage to the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

. This damage could be a result of neural degeneration, lack of oxygen in the brain, or other genetic factors. Any abnormal response for this reflex could produce suspicion for an underlying disease that would need to be addressed. That is why the elicitation of this grasp reflex is part of neurological examinations for newborns.

References

{{Reflex Reflexes Neonatology