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Firing rates were measured from motor units in the wrist extensor muscles at varying levels of voluntary contraction \u226410% maximal force. At each force level, the firing rate was measured with and without added muscle vibration, a maneuver that repetitively activates muscle spindles. In motor units from age-matched control subjects, the firing rate increased with successively stronger contractions as well as with the addition of vibration at each force level. In patients with primary lateral sclerosis, motor-unit firing rates remained stable, or in some cases declined, with progressively stronger contractions or with muscle vibration. We conclude that excitatory inputs produce a blunted response in motor neurons in patients with primary lateral sclerosis compared with age-matched controls. The potential explanations include abnormal activation of voltage-activated channels that produce stable membrane plateaus at low voltages, abnormal recruitment of the motor pool, or tonic inhibition of motor neurons. <\/jats:p>","DOI":"10.1152\/jn.00185.2005","type":"journal-article","created":{"date-parts":[[2005,4,14]],"date-time":"2005-04-14T00:33:46Z","timestamp":1113438826000},"page":"919-927","source":"Crossref","is-referenced-by-count":20,"title":["Motor Neuron Firing Dysfunction in Spastic Patients With Primary Lateral Sclerosis"],"prefix":"10.1152","volume":"94","author":[{"given":"Mary Kay","family":"Floeter","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ping","family":"Zhai","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rajiv","family":"Saigal","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yongkyun","family":"Kim","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jeffrey","family":"Statland","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"24","reference":[{"key":"R1","doi-asserted-by":"publisher","DOI":"10.1212\/WNL.41.2_Part_1.286"},{"key":"R2","doi-asserted-by":"publisher","DOI":"10.1093\/brain\/123.8.1688"},{"key":"R3","doi-asserted-by":"publisher","DOI":"10.1152\/jn.00946.2003"},{"key":"R4","doi-asserted-by":"publisher","DOI":"10.1113\/jphysiol.1976.sp011580"},{"key":"R5","doi-asserted-by":"publisher","DOI":"10.1113\/jphysiol.1973.sp010369"},{"key":"R6","doi-asserted-by":"publisher","DOI":"10.1016\/0168-5597(93)90131-8"},{"key":"R7","doi-asserted-by":"publisher","DOI":"10.1093\/brain\/awf114"},{"key":"R8","doi-asserted-by":"publisher","DOI":"10.1093\/brain\/awg036"},{"key":"R9","doi-asserted-by":"publisher","DOI":"10.1113\/jphysiol.1978.sp012567"},{"key":"R10","unstructured":"Doherty TJ, Chan KM, and Brown WF. 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