The relationship between rCBF at 2.5 min of ischemia and PcomA. Little variability in rCBF was observed in the hemispheres without PcomA, particularly if the contralateral hemisphere lacked PcomA as well. The greatest variability in rCBF was observed among hemispheres with PcomA when the contralateral hemisphere lacked PcomA. PcomA(-/-): PcomA absent in both hemispheres, n = 10; PcomA(-/+): PcomA absent in the ipsilateral hemisphere and present in the contralateral hemisphere, n = 11; PcomA(+/-): PcomA present in the ipsilateral hemisphere and absent in the contralateral hemisphere, n = 11; PcomA(+/+): PcomA present in both hemispheres, n = 8.