In vivo brain imaging techniques such as positron emission tomography and functional magnetic resonance imaging, which are associated with changes in cerebral blood flow (CBF), are widely used for the diagnosis and/or treatment of cerebral vascular impairments and neural disorders. Understanding cerebrovascular regulatory mechanisms is important matter to make effective use of brain imaging techniques in medicine. Animal studies of hemodynamics using rats and mice play an important role in clarifying the regulatory mechanisms of CBF at the microvascular level. Previously, most animal experiments used anesthesia for avoidance of pain and inhibition of motion artifacts caused by movements of the animal. However, anesthesia significantly affects the animal’s physiological condition, for example, by lowering respiratory and cardiac rates along with body temperature. We recently developed a new measuring technique that allows accurate assessment and determination of hemodynamic changes in conscious animals under maintenance of their physiological conditions. In the present paper, we will review the cerebrovascular regulatory mechanisms and discuss these mechanisms as revealed by our new measurement technique.

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Since the volitional movements are impaired in the subjects with a variety of basal ganglia or frontal lobe dysfunctions, the signals from the basal ganglia through the thalamus to the frontal cortex might be essential for the generation of these movements. Recently, we performed some experiments in Japanese monkeys, Macaca fuscata, and showed a couple of evidence that the basal ganglia-thalamocortical loop plays a role in the generation of volitional saccade eye movements. First, the time courses of preparatory activity in the thalamus and dorsomedial frontal cortex were different depending on the timing of self-initiated saccades. Furthermore, both inactivation and stimulation experiments indicated that these signals played a causal role. Second, we used the anti-saccade task to examine the neural mechanisms of self-controlled behavior. In this task, monkeys were instructed to suppress reflexive saccades to peripheral visual stimuli (pro-saccade), and instead make a saccade in the opposite direction (anti-saccade). The neuronal modulation in the basal ganglia and the motor thalamus was greater during anti-saccades than pro-saccades, and inactivation of these areas solely impaired anti-saccades. These results showed that the signals in the basal ganglia-thalamocortical pathways regulate the voluntary control of eye movements such as self-initiation and reflex suppression. This neural mechanism could be generalized to other motor systems and cognitive functions that are also regulated by the signals through the basal ganglia-thalamocortical pathways.

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[in Japanese]

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