Motor deficits in patients with large-fiber sensory neuropathy.

Abstract

The issue of whether brain signals in the absence of peripheral feedback are sufficient to specify accurate movement was evaluated by studying motor performance in patients with loss of somesthetic afferent input as a result of acquired large-fiber sensory neuropathy. With visual guid-ance, movements and postures were impaired relatively little, but when visual guidance was unavailable, the patients exhibited postural drift and gross inaccuracy of movement. Impairments were more apparent for smaller (3°) than for larger (15°) movements. Previous studies that have failed to show major motor impairments in deafferented subjects examined movements involving rather large joint displacements, and this may have been a factor in the failure of these studies to reveal severe deficits. The present results demonstrate a critical role for somesthetic feedback in regulating centrally generated levels of motor output and show that central motor programs deprived of such feedback are unable to subserve accurate motor control.Severe motor impairments in patients with large-fiber sensory neuropathies have been described by clinical neurologists (1-3) and are commonly observed in clinical practice, but results from a number of neuropsychological experiments have raised doubts as to the importance of sensory feedback in active movement (4-7). These "negative" studies revealed only slight motor deficits in deafferented humans, monkeys, cats, and a variety of invertebrates, and it was argued that centrally programmed brain or spinal cord activity could control movement without the need for sensory feedback (8).We reexamined this issue in patients with somesthetic losses due to acquired large-fiber sensory neuropathy, and our results help to resolve the discrepancies between clinical and neuropsychological investigations: whereas motor impairments may seem to be slight when deafferented subjects make relatively large limb displacements, impairments become progressively more apparent as movement size is reduced. Furthermore, somesthetic losses cause profound deficits in the ability of subjects to maintain the steady-state levels of active muscular contraction necessary for postural stability. MATERIALS AND METHODSThe patients who were studied had a peripheral neuropathy with selective involvement of large sensory fibers without clinically evident weakness. Thus, while having excellent muscular strength, the patients exhibited sensory deficits, including absence of position and vibration sense to the level of the most proximal joints; moderate decrease in pinprick, temperature, and light-touch sensation below the shoulders; and absence of deep-tendon reflexes. The loss of inputs fromThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. both cutaneous mechanoreceptors (as shown by deficits in tactile sensitivity) and from muscle receptors (as shown by loss of stretch reflexe...

Kinematics and end-point control of arm movements are modified by unexpected changes in viscous loading

“…According to this notion, an increase of viscosity opposing the movements of both normal and deafferented subjects would alter the intended velocity during movement from the initial to the terminal position, but would have no effect on intended terminal accuracy. These considerations underlie the theoretical implications of recent findings that deafferented humans fail to position a limb accurately after a viscous load is introduced during movement (Day and Marsden, 1982;Rothwell et al, 1982a;Sanes, 1983;Sanes et al, 1985). As mentioned above, if CNS signals in the absence of somesthetic feedback were able to specify movement end-points, then a change of viscous loading would alter movement trajectory but would not affect movement end-point.…”

“…This suggests that triggered muscle responses are compensatory in certain movement situations but disruptive in others. In addition, these findings demonstrated that dynamic loads especially affect the kinematics and end-point control of smaller movements, suggesting that kinesthetic inputs and central motor commands interact so subjects may achieve accurate positioning for certain classes of movements.Several recent studies of motor control in patients with sensory loss have described impairments of movement accuracy as a result of viscous-load changes occurring during movement (Day and Marsden, 1982;Nam et al, 1984;Rothwell et al, 1982a;Sanes et al, 1985). The reason for the use of viscous loads (as compared to springs or weights) in these studies was that viscous loads acted during displacement but not during absence of movement.…”

“…Several recent studies of motor control in patients with sensory loss have described impairments of movement accuracy as a result of viscous-load changes occurring during movement (Day and Marsden, 1982;Nam et al, 1984;Rothwell et al, 1982a;Sanes et al, 1985). The reason for the use of viscous loads (as compared to springs or weights) in these studies was that viscous loads acted during displacement but not during absence of movement.…”

Identification of a forebrain motor programming network for the learned song of zebra finches

“…There is much indirect evidence that the telencephalon participates in "programming" voluntary behavior (Bernstein, 1967;Rothwell et al, 1982Rothwell et al, , 1989Carter and Shapiro, 1984;Marsden et al, 1984;Sanes et al, 1985;Ghez et al, 199 I), including the findings that many different neurons in the telencephalon are more active before and during movement (Evarts, 1968;Brinkman and Porter, 1979;Bock et al, 1987;Humphrey and Freund, 1991;Mushiake et al, 1991;Kalaska et al, 1992). However, little evidence exists that localize a particular motor program to a discrete telencephalic brain area (Alexander et al, 1992).…”

Cutaneous mechanisms of isometric ankle force control

“…The results showed that stimulation decreased cutaneous sensory function as evidenced by increased touch threshold. Absolute dorsiflexion force on visual feedback to maintain accuracy (Rothwell et al 1982;Sanes et al 1984). In order to achieve fine force resolution in finger control, cutaneous feedback must be properly integrated with central motor command (Henningsen et al 1995(Henningsen et al , 1997.…”