Functional landscapes of the dominant hemisphere

Abstract

There is abundant evidence that in non-anoxic brain tissue the blood flow is controlled mainly by the functional activity of the neurons. This enables the use of regional blood flow measurements for the localization and quantitation of events in the human brain which correlate to normal and abnormal mental activity. Measurements of regional cerebral blood flow (rCBF) by means of the ¹³³Xe clearance technique have demonstrated that the activity distribution in the normal resting brain shows a typical ‘landscape’, with the highest activities in the premotor and frontal regions and the lowest in temporal and parietal ones. The resting pattern is readily changed by voluntary motor activity which gives a rolandic-postrolandic activity peak and by sensory stimulation which activates rolandic and prerolandic structures especially. Speech and reading activate the upper, anterior and posterior speech cortices, as well as the face, tongue and mouth area. Problem solving also activates premotor and frontal regions especially and, if visual activity is involved, the occipital pole is also activated. These normal patterns confirm by and large well known aspects of the functional anatomy of the human dominant hemisphere.

Brain lesions may alter the functional landscape of the dominant hemisphere profoundly. Most brain lesions cause a decrease of the general flow level and focal lesions give focal reductions which may be pronounced. A number of clinical correlations have been demonstrated between rCBF abnormalities and focal brain lesions caused by cerebrovascular disorders, brain trauma, brain tumors, epilepsy, and infectious disorders. In many such disorders, the above mentioned activation patterns are abnormal or absent, a fact often to be expected from the clinical symptomatology.

Finally, it has been found in patients with organic dementia that the flow level of the brain is reduced grossly in proportion to the intellectual deficit and, furthermore, that subsymptoms of the dementia correlate with regional flow abnormalities. Chronic schizophrenia also shows abnormalities of the rCBF landscape in spite of the fact that such patients retain a normal level of total mean cerebral blood flow and oxygen uptake. There appears to be a specific maldistribution of flow (function) in chronic schizophrenia with a low activity in frontal regions and high activity in postcentral ones. This pattern is possibly related to the perceptual and behavioral deficits which characterize this disorder.

The present review supports the notion that the rCBF technique may be used with advantage to localize and to quantify cerebral events which are related to normal and abnormal mental activity.