A loose upper bound on human memory can be established from a simple counting argument. Suppose a brain of mass $m$ fits in a sphere of radius $r$. Then, the mass-energy of the brain is at most: $$ E=mc^{2} $$ Applying Bekenstein's bound, the maximum information in that sphere is: $$ I\leq\frac{2\pi Er}{\hbar c\ln 2} $$ Thus, the brain can have no more than $2^{I}$ distinct states. If a distinct memory minimally requires a distinct state, then the brain can have no more than $2^{I}$ distinct memories. This, for a brain of mass $1.4$ kg that fits in a sphere of radius $0.1$ m, is approximately: $$ 2^{3.6\times 10^{42}} $$