Responses of rat trigeminal ganglion neurons to movements of vibrissae in different directions.

The response properties of 123 trigeminal ganglion neurons were studied, using controlled whisker deflections in different directions. When the distal end of the whisker was initially displaced 5.7 degrees (1 mm) from its neutral position, 81% of the cells responded with statistically more spikes/stimulus to movements in one to three of eight cardinal (45 degrees increment) directions than to the others. The more directionally selective the cell, the more vigorous was its response. On the basis of statistical criteria, 75% of the cells were classified as slowly adapting, 25% as rapidly adapting. A number of quantitative analyses indicated that slowly adapting units respond more selectively than rapidly adapting cells to the direction of whisker movement. Differences in directional sensitivities of rapidly and slowly adapting cells appear to parallel differences between their putative mechanoreceptive endings and the relationships between those endings and the vibrissa follicle's structure. Comparisons between the response properties of peripheral and central neurons in the vibrissa-lemniscal system indicate that the afferent neural signal is progressively and substantially transformed by mechanisms that function to integrate information from different peripheral receptors and from different, individual vibrissae.