Title : Modulation and Transmission of Peripheral Inputs in Monkey Cuneate

22 Somatosensory signals undergo substantial modulation in the dorsal column nuclei. We examined transmission 23 of signals from forelimb afferents in primate cuneate and external cuneate nuclei. In anaesthetised macaque 24 monkeys, the median, ulnar, deep radial and superficial radial nerves were electrically stimulated at 1.5-2x 25 motor threshold with independent Poisson trains whilst extracellular recordings were made from 317 cells. 26 Responses to peripheral stimulation included instances of both brief facilitation and long lasting suppression. A 27 high proportion of cells (87%) responded to stimulation of two or more peripheral nerves, suggesting a large 28 amount of convergence. Facilitated cells showed coherence with the peripheral stimulation across a broad 29 frequency range; coherence was especially high in cells which responded with a burst of action potentials. Cells 30 which responded with suppression also showed significant coherence, but this fell rapidly for frequencies above 31 25 Hz. Similar results were seen in both the main and external cuneate. 32 When stimulation of one nerve was conditioned by a preceding nerve stimulus, the response to the second 33 stimulus was attenuated for around 40 ms. This occurred independently of whether the first stimulus produced 34 an initial facilitation or suppression, or whether the same or a different nerve served as a conditioning stimulus. 35 Mechanical stimulation of a receptive field suppressed responses to a second identical mechanical stimulus over 36 a similar timescale. We conclude that the primate cuneate nucleus is capable of transmitting temporal 37 information about stimuli with high fidelity; stimuli interact both temporally and spatially to modulate the 38 onward transmission of information. 39