Startle reflex

 
Babies, until the age of 3-4 months will display the startle reflex where they throw out both their arms as if having had a sudden scare.  The presence if this shows a nervous system that is working.   Theoretically, the thought is that when we were cavemen, this reflex was a primitive safety reflex.  Imagine we were a hairy race, I mean long hair all over our bodies.  If someone was holding a baby and for some reason the baby was to fall or be dropped, the reflex would provide a possibility of safety.

Babies also have a strong grasp reflex.  This is when we put our finger in their palm, they will grasp it very tightly. So, in the scenario mentioned, when a baby falls , they will startle, and whatever their palms touch, they will grasp onto.

The startle reflex comes into play with sleep also.  As with a lot of us, when we are going off to sleep, sometimes there is a sense of falling.  That is why  babies will show  the startle reflex when they are going off to sleep.  Often, but not always, this can wake them up, when they were almost off to sleep.

Babies sometimes will startle when they come into a light sleep state  for the same reason.

It is for this reason that we encourage young babies(under 3 months), to be wrapped or swaddled to go off to sleep.  Being swaddled gives them a sense of security when they startle by offering a firm resistance to their arms when they lift them in a startle.

Babies go to sleep easily when being cuddled against your chest  too. They can’t startle because their arms are next to your chest and can’t physically  reach out because your chest is stopping it.

By the way, babies sleep well on their tummies because they can’t startle.  Tummy sleeping is strongly discouraged because of SIDS risks.  This has been proven over years of research from this wonderful organisation.

Primitive cultures also note this. Through research, it has been shown that these cultures instinctively also put their babies to sleep on their backs for the same reason.