Jones E G
Department of Anatomy and Neurobiology, University of California, Irvine 92717.
Ciba Found Symp. 1987;132:21-39. doi: 10.1002/9780470513545.ch3.
Modern anatomical studies show that, contrary to the long-held dogma, there appears to be essentially no convergence of lemniscal, cerebellar, pallidal, or substantial nigral afferents in the thalamus. Each afferent stream defines its own thalamic territory and, through the projection of these thalamic territories to separate cortical territories, the independence of the projections of subcortical motor nuclei upon the cortex is preserved. Only the spinothalamic system appears to gain access to both sensory and motor cortex. A further principle of organization in the sensorimotor thalamus is the presence of individual anatomically and physiologically defined channels, composed of separate afferent inputs and groups of neurons relaying to the cortex. In the somatic sensory relay nuclei the dissociation of cutaneous, deep slowly and rapidly adapting channels is clear-cut in the thalamus and at the input level of the cortex. In the motor system, inputs from each of the deep cerebellar nuclei appear to be dissociated from one another in the thalamus and these in turn from the vestibular and spinothalamic systems. Just as pallidal, nigral and cerebellar pathways are in position to control separate premotor and motor areas of the cortex, so separate channels leading through VLp appear to be in a position to control separate functional units in area 4. Within the cortex itself the absence of corticocortical connections passing from areas 3a and 3b to area 4 appears to indicate that information flow out of these areas is back to areas 1 and 2 for further processing before transmission to area 4 with all the consequences that entails for sensory convergence. Presumably, this route is sufficiently rapid for sensory inputs to reach area 4 at short latency. Although many data are beginning to accrue on the intrinsic structure and connectivity of the sensorimotor cortex, we are still distant from a complete wiring diagram. Circuitry involving thalamic afferents is becoming known slowly and the nature of the cells that are present and their transmitter characteristics are becoming evident from morphological and immunocytochemical studies, along with information on the patterns of axonal ramification of specific cell types, especially of GABAergic cells and of excitatory corticocortical cells.
现代解剖学研究表明，与长期以来的教条相反，丘脑内似乎基本不存在感觉神经、小脑、苍白球或黑质传入纤维的汇聚。每条传入纤维束都界定了自己的丘脑区域，并且通过这些丘脑区域向不同皮质区域的投射，皮质下运动核团向皮质投射的独立性得以保留。只有脊髓丘脑系统似乎能够连接感觉皮质和运动皮质。感觉运动丘脑组织的另一个原则是存在个体在解剖学和生理学上定义的通道，这些通道由单独的传入输入和向皮质中继的神经元群组成。在躯体感觉中继核中，皮肤、深部慢适应和快适应通道在丘脑以及皮质的输入水平上的分离是明确的。在运动系统中，来自每个小脑深部核团的输入在丘脑中似乎相互分离，并且这些输入又与前庭和脊髓丘脑系统分离。正如苍白球、黑质和小脑通路能够控制皮质不同的运动前区和运动区一样，通过腹外侧后核（VLp）的不同通道似乎能够控制4区的不同功能单元。在皮质本身内部，从3a区和3b区到4区不存在皮质-皮质连接，这似乎表明从这些区域流出的信息流会回到1区和2区进行进一步处理，然后再传输到4区，这对感觉汇聚具有所有相关影响。据推测，这条路径足够快，使感觉输入能够在短潜伏期内到达4区。尽管关于感觉运动皮质的内在结构和连接性的许多数据开始积累，但我们距离完整的布线图仍有很大差距。涉及丘脑传入纤维的回路正逐渐为人所知，从形态学和免疫细胞化学研究以及关于特定细胞类型，特别是GABA能细胞和兴奋性皮质-皮质细胞的轴突分支模式的信息中，存在的细胞的性质及其递质特征正变得明显。
