crying and vegetative sounds are controlled by the brain stem, which matures earlier than the cortex. neurological development of higher brain structures coincides with certain developments in infants’ vocalizations. for example, the onset of cooing at 6 to 8 weeks happens as some areas of the limbic system begin to function. the limbic system is known to be involved in the expression of emotion, and cooing in infants is associated with a feeling of contentedness. further development of the limbic system might be responsible for the onset of laughter around 16 weeks of age. the motor cortex, finally, which develops later than the abovementioned structures may be necessary for canonical babbling, which start around 6 to 9 months of age.