Normally, the concentration of solutes in our brain cells would be the same as the concentration of the cerebrospinal fluid. Thus, they form an isotonic solution.
The volume of a human brain is normally about 1,200cm3. The concentration of solutes in the cerebrospinal fluid (the fluid that surrounds the brain and other parts of the central nervous system) is normally about 300mM.
It would be hypotonic solution as there is less concentration of solute outside than inside.
