Summary: Let $(R,\frak {m})$ be a standard graded $K$-algebra over a field $K$. Then $R$ can be written as $S/I$, where $I\subseteq (x_1,\ldots ,x_n)^2$ is a graded ideal of a polynomial ring $S=K[x_1,\ldots ,x_n]$. Assume that $n\geq 3$ and $I$ is a strongly stable monomial ideal. We study the symmetric algebra ${\rm Sym}_R({\rm Syz}_1(\frak {m}))$ of the first syzygy module ${\rm Syz}_1(\frak {m})$ of $\frak {m}$. When the minimal generators of $I$ are all of degree 2, the dimension of ${\rm Sym}_R({\rm Syz}_1(\frak {m}))$ is calculated and a lower bound for its depth is obtained. Under suitable conditions, this lower bound is reached.\looseness -1