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This Article Full Text Full Text (PDF) All Versions of this Article: 102/1/85    most recent 91113.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Seki, K. Articles by Fetz, E. E. PubMed PubMed Citation Articles by Seki, K. Articles by Fetz, E. E.

Task-Dependent Modulation of Primary Afferent Depolarization in Cervical Spinal Cord of Monkeys Performing an Instructed Delay Task

¹Department of Developmental Physiology, National Institute for Physiological Sciences, Okazaki, Aichi, Japan; and ²Department of Physiology and Biophysics, and Washington National Primate Research Center, University of Washington, Seattle, Washington

Submitted 4 October 2008; accepted in final form 14 April 2009

Task-dependent modulation of primary afferent depolarization (PAD) was studied in the cervical spinal cord of two monkeys performing a wrist flexion and extension task with an instructed delay period. We implanted two nerve cuff electrodes on proximal and distal parts of the superficial radial nerve (SR) and a recording chamber over a hemi-laminectomy in the lower cervical vertebrae. Antidromic volleys (ADVs) in the SR were evoked by intraspinal microstimuli (ISMS, 3–10 Hz, 3–30 µA) applied through a tungsten microelectrode, and the area of each ADV was measured. In total, 434 ADVs were evoked by ISMS in two monkeys, with onset latency consistently shorter in the proximal than distal cuffs. Estimated conduction velocity suggest that most ADVs were caused by action potentials in cutaneous fibers originating from low-threshold tactile receptors. Modulation of the size of ADVs as a function of the task was examined in 281 ADVs induced by ISMS applied at 78 different intraspinal sites. The ADVs were significantly facilitated during active movement in both flexion and extension (P < 0.05), suggesting an epoch-dependent modulation of PAD. This facilitation started 400–900 ms before the onset of EMG activity. Such pre-EMG modulation is hard to explain by movement-induced reafference and probably is associated with descending motor commands.