Akbarian S, Grüsser O J, Guldin W O
Department of Physiology, Freie Universität Berlin, Germany.
J Comp Neurol. 1994 Jan 15;339(3):421-37. doi: 10.1002/cne.903390309.
The distribution of cortical efferent connections to brainstem vestibular nuclei was quantitatively analysed by means of retrograde tracer substances injected into different electrophysiologically identified parts of the brainstem vestibular nuclear complex of five Java monkeys (Macaca fascicularis). Three polysensory vestibular areas were found to have a substantial projection to the vestibular nuclei: area 2v located at the tip of the intraparietal sulcus, the parietoinsular vestibular cortex (PIVC) covering the most occipital part of the granular insula (Ig) and the retroinsular area (Ri or reipt), and the dorsolateral part of the somatosensory area 3a ("area 3aV" neck/trunk region). From physiological recording experiments, these three cortical fields were known to contain many neurons responding to stimulation of semicircular canals as well as to optokinetic (area 2v, PIVC) and somatosensory stimuli (PIVC, area 3a). These three regions form the inner cortical vestibular circuit. Besides these polysensory vestibular cortical fields, three other circumscribed cortical regions of the macaque brain were also found to project directly to the brainstem vestibular nuclei: a circumscribed part of the postarcuate premotor cortex (area 6pa), part of the agranular and the adjacent dysgranular cortex located around the cingulate sulcus (area 6c/23c), and a predominantly visual (optokinetic) association field located at the fundus of the lateral sulcus (area T3). These areas are known to have connections with the structures of the inner cortical vestibular circuit. Only a few efferent connections to the brainstem vestibular nuclei were found for the different parts of cytoarchitectonic area 7. Significant differences were found between the efferent innervation patterns of the axons originating in the six cortical areas mentioned and ending in the various compartments of the vestibular nuclear complex. Vestibular nuclei with a dominant output to the gaze motor system of the brainstem receive efferent connections preferably from the parietoinsular vestibular cortex. Vestibular structures with their primary output to skeletomotor centers, however, receive stronger efferent connections from areas 6pa and 3a. The ventrolateral nucleus, which sends efferent axons to both the oculomotor and skeletomotor systems of the brainstem and the spinal cord, also receives its main cortical efferents from the somatomotor area 6 and from area 3aV. Through these connections the cortical somatomotor system may directly influence vestibuloocular and vestibulocollic reflexes. It is speculated that the corticofugal connections to the vestibular brainstem nuclei are predominantly inhibitory, suppressing vestibular reflexes during cortically controlled goal-directed movements.
通过将逆行示踪剂注入五只爪哇猴（食蟹猴）脑干前庭核复合体不同电生理确定部位，对皮质传出纤维与脑干前庭核的连接分布进行了定量分析。发现三个多感觉前庭区域向前庭核有大量投射：位于顶内沟尖端的2v区、覆盖颗粒岛叶（Ig）最枕部的顶岛前庭皮质（PIVC）和岛后区（Ri或reipt），以及体感区3a的背外侧部分（“3aV区”颈部/躯干区域）。从生理记录实验可知，这三个皮质区域包含许多对半规管刺激、视动刺激（2v区、PIVC）和体感刺激（PIVC、3a区）有反应的神经元。这三个区域构成了皮质内前庭回路。除了这些多感觉前庭皮质区域外，还发现猕猴大脑的其他三个限定皮质区域也直接投射到脑干前庭核：弓形后运动前皮质的一个限定部分（6pa区）、位于扣带沟周围的无颗粒和相邻颗粒减少皮质的一部分（6c/23c区），以及位于外侧沟底部的主要视觉（视动）联合区（T3区）。已知这些区域与皮质内前庭回路的结构有联系。在细胞构筑7区的不同部分，仅发现少数与脑干前庭核的传出连接。在源自上述六个皮质区域并终止于前庭核复合体各个分区的轴突传出支配模式之间发现了显著差异。对脑干凝视运动系统有主要输出的前庭核，优先接受来自顶岛前庭皮质的传出连接。然而，主要输出到骨骼运动中枢的前庭结构，接受来自6pa区和3a区更强的传出连接。腹外侧核向脑干和脊髓的动眼和骨骼运动系统发送传出轴突，其主要皮质传出纤维也来自躯体运动区6和3aV区。通过这些连接，皮质躯体运动系统可能直接影响前庭眼反射和前庭颈反射。据推测，与前庭脑干核的皮质传出连接主要是抑制性的，在皮质控制的目标导向运动期间抑制前庭反射。
