The laminar organization of dorsal horn and effects of descending impulses.

1. An examination of the physiological properties of cells in cat lumbar dorsal horn shows that there are three horizontal laminae which correspond approximately to Rexed (1952) laminae 4, 5, and 6.2. A summary diagram (Fig. 9) suggests the relation of the laminae to each other and to afferent and descending fibres. All three laminae respond to cutaneous stimulation but only lamina 6 responds to movement. By comparing responses of cells in decerebrate and spinal preparations, it is shown that the brain stem inhibits cutaneous responses and enhances movement responses. Pyramidal tract stimulation affects cells in laminae 4, 5, and 6.3. Cells in lamina 4 have small cutaneous receptive fields and respond as though many different types of specific cutaneous afferents converge on them. Cells in lamina 5 respond as though many cells of lamina 4 converge on them. In the decerebrate animal the responses of lamina 5 cells habituate to repeated light pressure stimuli but the cells remain responsive to new stimuli in other parts of their receptive field. Impulses descending from the brain stem can switch the modality of lamina 6 cells from cutaneous to proprioceptive.