There has never been a study of the relation between the emergence of a day-night rhythm and the mental leaps. We do know that children begin to form a day-night rhythm between two and three months, but that rhythm is still shifting a little. Your baby starts to sleep well all through the night, but does not fall asleep at the same time and does not yet awake at the same time. By the time your baby is 15 weeks old, you'll notice that there is a more stable pattern in his day-night rhythm.

The day-and night rhythm is also called the circadian rhythm. You can assist your baby in finding this rhythm by ensuring that the difference between day and night is very clear. During the night it is dark and you do not turn on a lamp as he cries and you go to feed or comfort him. You speak softly when he wakes up. By giving these visual and auditory signals, you make the differences between day and night more clear to your baby, and this will help him develop a better circadian rhythm.