A palmomental reflex occurs when stroking the palm of the hand (on the ball of the thumb / thenar) causes the ipsilateral mentalis muscle (lower lip muscle on the same side as the hand tested) to contract, elevating the lower lip slightly.The reaction is made possible by the ulnar and median nerves in the arm.
This difficult to elicit and little researched reflex is remarkable because of the distance between the reflexogenic zone and the effector.
The reflex is considered a frontal release sign. At older age it is inhibited by frontal lobe activity in the brain, but can be "released" from inhibition if the frontal lobes are damaged. The reflex is normally present in infancy until about one year of age (the present baby boy is 3 months of age).
By the way, at 0:29 notice the startle reflex in the right arm of the baby after my loud voice.
For more baby reflexes check my playlist:
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