TED Summary : The benefits of Bilingual Brain
Knowing and learning other language beside your mother language brings several benefits for our brain. The speaker said that the brain works differently when we speak or learn bilingual (multilingual). Children easily learn other language because they use both of their brain hemisphere while adult only use the left one. Having more than one language also brings some remarkable advantages for both children and adult. The children or adult learning more than one language will have less emotional problems and help them to prevent the brain diseases such as dementia. Although it is not make us smarter, our brain will be more healthy, complex and actively engaged.
Your text will sound much better if you reformulate some of the sentences as follows:
Knowing and Learning [...] a foreign language is believed to be very beneficial for one's brain. The speaker said [...] It is commonly assumed that... or learn bilingual (multilingual) [...] some other language.
hemispheres while adults...(this statement is incorrect).
Having [...]Being fluent in...
children and adults.
The children or adult learning ... [...] Those children and adults who know more than one language will...
and this will help them [...] not to succumb to a number of different neurological diseases, such as dementia.
it is not make us smarter [...]one's proficiency in a foreign language will not make him or her smarter...
I hope this will help. Regards.