Neurovascular microsurgery: a model for laboratory investigation and the development of technical skills.

An inexpensive and reproducible model to help in developing the technical skills for, and to investigate experimentally, a microvascular anastomosis resembling the superficial temporal-middle cerebral artery bypass is described. The model is used to illustrate the important principles of microvascular surgery. Using a standardized operative technique, we evaluated 50 successive preparations by perfusion; the patency rate was 100%.     

Selective adaptation of “command neurons” in the human motor system

It is proposed that motor activity is largely controlled by a neural hierarchy, with cells at successively higher levels commanding movements which involve increasing numbers of muscles. The existence of cells which command similar action patterns in different muscle groups can account for some types of motor equivalence. To test for the presence of such cells, the psychophysical technique of selective adaptation was applied to movement. Before performing a movement with one arm as often as possible in a fixed period of time, subjects performed either the same or a different movement with the other arm (Experiments I, II, III) or with the same arm (Experiment IV). Performance of repeated movements was worse than performance of different movements. The results are taken as tentative evidence for the existence of command neurons controlling similar movements in different arms and particular movements in each arm.     

Comparative cranial CT enhancement in a primate model of cerebral infarction

The value of various enhancement techniques as opposed to nonenhanced CT scanning was compared in 15 baboons with cerebral infarction secondary to embolization of the left middle cerebral artery. The most prominent CT findings in infarction included an area of low absorption in the opercula--basal ganglia--centrum semiovale region and generalized lateral ventricular enlargement. Intravenous enhancement of the low-density region occurred in 25% of the animals and often obscured the preenhancement abnormality. However, a rapid bolus injection of contrast material followed by immediate consecutive CT scans (computed angiotomography) permitted prominent visualization of early-shunting veins. Delayed scanning following intrathecal enhancement better defined small infarctions that did not exhibit the usual cerebral blush. The CT imaging of inhaled xenon provides a new technique for evaluating subtle abnormalities in cerebral perfusion, even when the routine CT scan shows no abnormality.