Sorry for unearthing an old thread, but some books say that if the lesion is above the red nucleus of the midbrain, and thus preserving the rubrospinal tracts(red nucleus preferentially activates the flexors) then you will see decorticate posturing (flexion). If below the red nucleus, then Rubrospinal tracts are gone, and we have unopposed influence from the much lower vestibular nuclei and vestibulospinal tracts (which preferentially activate ipsilateral extensors), causing limb extension, and decerebrate posturing.

Hope it helps, I love neuroanatomy...

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Ross University School of Medicine, MS4

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