It is present in infancy and disappears as the brain matures during childhood but may reappear due to processes that disrupt the normal cortical inhibitory pathways.
The thenar eminence is stroked briskly with a thin stick, from proximal (edge of wrist) to distal (base of thumb) using moderate pressure.
[1] In their seminal 1920 paper, Gheorghe Marinescu and Anghel Radovici hypothesized that both the afferent (receptive) and efferent (motor) arms of the reflex are on the same side (ipsilateral) to the hand stimulated;[2] this hypothesis remains unsubstantiated.
These include congenital conditions such as Down syndrome, where it is unclear whether the reflex persists throughout life, or disappears and then re-appears in association with the onset of Alzheimer disease pathology.
[1] A study conducted in a neurosurgical in-patient population showed there is no significant association between the side of the reflex and the side of the hemispheric lesion in patients with unilateral (one-sided) reflexes and unilateral (one-sided) lesions.