# Roots **URL:** \ **Category:** CSG1998\ **Created:** [March 5, 1998, 2:56am UTC](http://discourse.iapct.org/t/roots/10075 "1998-03-05T02:56:33Z")\ **Posts on this page:** 2\ **Page:** 1

**Author:** ![Fred\_Nickols3](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/f/9de053/32.png) [@Fred\_Nickols3](http://discourse.iapct.org/u/Fred_Nickols3)\ **Post date:** [March 5, 1998, 2:56am UTC](http://discourse.iapct.org/t/roots/10075/1 "1998-03-05T02:56:33Z")

[Fred Nickols (980304.2145 EST)] Bill Powers (980304.0415 MST)-- > When I first learned about negative feedback, I was 18 years old and in the > Navy electronics course. Me, too. > We were learning about negative feedback in > amplifier circuits. Me, too. > Our instructor took us through the feedback equations > and showed that with enough feedback, the input-output function was > determined almost completely by the feedback components, with the forward > vacuum-tube characteristics disappearing from the equations. So we could > get a nice linear response from nonlinear components. > > After this had been clearly demonstrated, the instructor then asked why, if > the vacuum tube's gain and linearity no longer mattered, we couldn't just > pull out the 6L6 vacuum tubes altogether. I promptly forgot all that stuff, although I seem to have a dim recollection of athe 6L6 as a power amplifier, usually the last vacuum tube before the output transformer in old-fashioned stereo systems, for example. By the way, I received my new copy of B:CP today (darned if I can find the one I bought in 1975). It came shrink-wrapped so tightly I had to use a knife to open it (fingernails couldn't get the job done). I'll dive back in once I've worked through B:CP again. Regards, Fred Nickols The Distance Consulting Company nickols@worldnet.att.net [http://home.att.net/~nickols/distance.htm](http://home.att.net/~nickols/distance.htm) ---

**Author:** ![Tom\_BOURBON3](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/t/85e7bf/32.png) [@Tom\_BOURBON3](http://discourse.iapct.org/u/Tom_BOURBON3)\ **Post date:** [May 12, 1993, 5:22pm UTC](http://discourse.iapct.org/t/roots/10075/2 "1993-05-12T17:22:37Z")

> From Tom Bourbon (930512.1050) A few days ago, in his long (but not exhaustive) list of misconceptions about PCT, Rick Marken mentioned the old chestnut in which certain people who should know better (and who probably do) claim that cutting the sensory roots of spinal nerves (rhizotomy, or deafferentation) eliminates all sensory connections to the spinal cord but has no effect on behavior, therefore sensory feedback is not essential to behavior, therefore PCT is a crock. Aside from the indisputable fact that behavior is not the same after deafferentation, there is another interesting problem with that old argument: Cutting the so-called sensory roots of spinal nerves does not eliminate sensory connections to the cord. Just a few days ago, I discovered that my recently nomadic career path has led me to a department chairman (Guy Clifton) who, in spite of looking too young to have dome so, produced some of the physiological data that, along with anatomical observations (some of them very old), comprise the complete refutation of the venerable Bell-Magendie Law (aka the Law of Spinal Roots). That law asserts that the fibers in dorsal roots of spinal nerves are sensory; those in ventral roots, motor. In spite of its near-universal acceptance, the "Law" is false. I will not present all of the details, but for those who have previously expressed interest in this topic (Gary C., I know you have), I will summarize the evidence against Bell-Magendie\Roots and will give a few citations that might be useful the next time a motor-plan\program(me) person tries to back a lone PCTer into the corner and shout, "deafferentation!" First the anatomy. As long ago as 1894, C. S. Sherrington described evidence that there are about 5 to 40 large myelinated sensory fibers in each ventral (putatively motor) root. Not very many, but a start at chipping away at the exclusionary "Law." The count of myelinated sensory fibers in ventral roots has held nearly constant in studies on mammalian species ever since. (Sherrington CS. On the anatomical constitution of nerves of skeletal muscles with remarks on recurrent fibers in the ventral spinal root. Journal of Physiology 1894;17:211-258) (There were similar reports even earlier than Sherrington's.) All through the late 1800s and early 1900s, there were reports of "recurrent" (that is, afferent or sensory) fibers in ventral roots -- a veritable lost literature that refutes the treatment of spinal roots in every text from which I ever studied or taught. (There are many citations of this literature in the more recent references I am about to describe. People interested in this topic should take an afternoon and browse through some of the many citations. It is an eye-opening experience.) By the late 1960s to mid 1970s, the evidence was in that there are far more sensory fibers than Sherrington found. Most of them are small, unmyelinated fibers that were not seen in some of the earlier procedures, or were discounted when they were seen. For over 25 years now, study after study has shown that from 25% to 30% of ventral root neurons are small and unmyelinated and that half of those are sensory. Therefore, about 12% to 15% of ventral root neurons are small, unmyelinated sensory fibers. (And there are the 5 to 40 large myelinated ones.) There is a large (and largely unknown) literature in which people suggest that these ventral root sensory neurons probably explain the common failure of rhizotomy (the cutting of dorsal roots) as a treatment for chronic pain and other disorders. Meanwhile, the cutting continues. By the early to mid 1970s, there were good physiological data that identified the effective stimuli for many ventral sensory neurons, and that mapped out their receptive fields. Many of these neurons serve the connective tissues and the viscera. (So what could they possibly have to do with overt skeletomuscular behavior, your critics will ask? And you will know how to reply.) Guy was a young medical student in those days and worked in a lab at the University of Texas Medical Branch in Galveston, where I recently stopped off for a while in my wanderings. I will give a few citations of their work. They were good scholars -- they included many references to the extensive earlier literature. Clifton GL, Vance WH, Applebaum ML, Coggeshall RE, Willis WD. Responses of unmyelinated afferents in the mammalian ventral root. Brain Research 1974;82:163-167. Coggeshall RE, Clifton GL, Vance WH, Applebaum ML. Unmyelinated axons in the ventral root. Anatomical Record 1975;181:334. Applebaum ML, Clifton GL, Coggeshall RE, Coulter JD, Vance WH, Willis WD. Unmyelinated fibres in the sacral 3 and caudal 1 ventral roots of the cat. Journal of Physiology 1976;256:557-572. Clifton GL, Coggeshall RE, Vance WH, Willis WD. Receptive fields of unmyelinated ventral root afferents in the cat. Journal of Physiology 1976;256:573-600. I stumbled across this literature recently while looking for material to refute some invocations of "The Law" and of deafferentation that some motor-programme people were using to muddy up the neurophysiological literature. My first thought was that it must have been Guy's father. When I asked him if he were old enough to have done the work, he was startled. To paraphrase only lightly, "You mean you read that? I don't think anyone else ever did." Along the line of refuting classic assumptions, someone might want to look in The British Medical Journal for July 17, 1909, pages 125-132. That is the text of an address by Sir Victor Horsley, The Lincare Lecture on The Function of the So-Called Motor Area of the Brain, a lecture delivered before the master and fellows of St. John's College, Cambridge, May 6, 1909. He reports on his work from as early as 1885. I think you can get the general theme from the title. Classic mistakes die hard. Sometimes it seems they never will. Until later, Tom Bourbon