We study the symmetric subquotient decomposition of the associated graded algebras A * of a non-homogeneous commutative Artinian Gorenstein (AG) algebra A. This decomposition arises from the stratification of A * by a sequence of ideals A * = C A (0) ⊃ C A (1) ⊃ • • • whose successive quotients Q(a) = C(a)/C(a + 1) are reflexive A * modules. These were introduced by the first author [I4, I5], developed in the Memoir [I6], and have been used more recently by several groups, especially those interested in short Gorenstein algebras, and in the scheme length (cactus rank) of forms.For us a Gorenstein sequence is an integer sequence H occurring as the Hilbert function H = H(A) for an AG algebra A, that is not necessarily homogeneous. Such a Hilbert function H(A) is the sum of symmetric non-negative sequences H A (a) = H Q A (a) , each having center of symmetry (j − a)/2 where j is the socle degree of A: we call these the symmetry conditions, and the decomposition D(A) = H A (0), H A (1), . . . the symmetric decomposition of H(A).We here study which sequences may occur as the summands H A (a): in particular we construct in a systematic way examples of AG algebras A for which H A (a) can have interior zeroes, as H A (a) = (0, s, 0, . . . , 0, s, 0). We also study the symmetric decomposition sets D(A), and in particular determine which sequences H A (a) can be non-zero when the dual generator is linear in a subset of the variables (Theorem 1.38).Several groups have studied "exotic summands" of the Macaulay dual generator F : these are summands that involve more successive variables than would be expected from