How do I perform a repeated measures analysis of variance in SPSS?

The key thing here is that each combinatio of the repeated measures factors is represented by a separate column. By contrast, all the levels of a between subject factor are entered in the same column.

For example suppose we wish to compare activity in four areas of the brain - the hippocampus, area 23, areas 29 and 30 and acingulate congulate. Activity in each of these areas is entered in four columns called hippo, a23, a29 and acin respectively.

The syntax below does this by specifying a with subjects factor, region, with four levels made up of each of the four columns. You can also use the repeated measures option in the General Linear Model menu.

If in addition you think that the acingulate congulate will show less activity than the other three areas you can test this using /MMATRIX subcommand. This subcommand is only available using syntax. It specifies contrast coefficients for each of the levels of the repeated measures factor.

filter by group.
GLM
  hippo a23 a29 acin
  /WSFACTOR = region 4 Polynomial
  /METHOD = SSTYPE(3)
  /CRITERIA = ALPHA(.05)
  /MMATRIX "Hip_a23_a29v.acin" all -0.333 -0.333 -0.333 1
  /WSDESIGN = region.

An equivalent form of the /MMATRIX subcommand above is

/MMATRIX "Hip_a23_a29v.acin" hippo -0.333 a23 -0.333 a29 -0.333 acin 1

Note the contrast coefficients sum to zero and specify a paired t-test comparing the activity means of the hippocompus, areas 23, 29/30 with that of the acingulate congulate.