A MODIFIED VERSION OF THE CENTER-OF-MASS BALANCING HYPOTHESIS
Book review of Roberts on Posture-Locomotion

Abstract

We specifically comment on Roberts' account (1995) of the interaction of vestibular and neck reflexes by contrasting it with an alternative view. While concurring with most of his formal description of the reactions resulting from a variety of experimental manipulations, we try to put the interpretation of these reactions according to our view into a broader systems perspective. According to this view, body stabilization requires two distinct sequences of coordinate transformations: one chains the sensory signals arising in the head "down" to the central representations of the trunk, the legs and, ultimately, to the feet and their support, while the second chain of transformations relays information from the feet back to the legs and trunk representations. Vestibular-neck interaction would reflect but one transformation step of these chains. Our concept of coordinate transformation owes much to recent progress in vestibular psychophysics. We suggest that vestibular psychophysics may indeed fill the gap between the physiological basis (e.g., vestibulo- spinal and cervico-spinal reflexes in the decerebrate cat) on the one hand, and, on the other hand, the complex task of decoding the centrally evoked discharge pattern by naturally occurring stimuli, which may call for a Gestalt recognition mechanism as suggested by Roberts.

Keywords

References

• Anastasopoulos, D. & Mergner, T. (1982) Canal-neck interaction in vestibular nuclear neurons of the cat. Exp. Brain Res., 46: 269-280.
• Boyle, R. & Pompeiano, O. (1981) Convergence and interaction of neck and macular vestibular inputs. J. Neurophysiol., 45.
• Britton T.C., Day B.L., Brown P., Rothwell J.C., Thompson P.D. & Marsden, C.D. (1993) Postural electromyographic responses in the arm and leg following galvanic vestibular stimulation in man. Exp. Brain Res., 94:143-151.
• Coulter, J.D., Mergner, T. & Pompeiano, O. (1976) Effects of static tilt on cervical spinoreticular tract neurons. J. Neurophysiol., 39:45-62.
• Hlavacka, F., Krizkova, M., Bodor, O. & Mergner, T. (1996) Adjustment of equilibrium point in human stance following galvanic vestibular stimulation: Influence of trunk and head position. In: Motor Control VII. Gantchev, G., Gurfinkel, V., Stuart, D. & M. Wiesendanger (eds). Motor Control Press, Tuscon, Arizona, p 289-293.
• Hlavacka, F., Mergner, T., Bolha, B. (1996) Human self-motion perception during translatory vestibular and proprioceptive stimulation. Neurosci. Lett, 210: 83-86.
• Lindsay, K.W., Roberts, T.D. & Rosenberg, J.R. (1976) Asymmetric tonic labyrinth reflexes and their interaction with neck reflexes in the decerebrate cat. J. Physiol. (Lond.) 261:583-601.
• Lund, S. & Broberg, C. (1983) Effects of different head positions on postural sway in man induced by a reproducible vestibular error signal. Acta Physiol. Scand., 117:307-9.
• Manzoni, D., Pompeiano, O., Srivastava, U.C. & Stampacchia, G. (1983) Responses of forelimb extensors to sinusoidal stimulation of macular labyrinth and neck receptors. Arch. Ital. Biol., 121:205-14.
• Maurer, C., Kimmig, H., Trefzer, A.& Mergner, T. (1997) Visual object localization through vestibular and neck inputs. I. Localization with respect to space and relative to the head and trunk mid-saggital planes. J Vestib Res (in press).
• Mergner, T., Becker, W. & Deecke, L. (1985) Canal-neck interaction in vestibular neurons of the cat's cerebral cortex. Exp. Brain Res., 61:94-108.
• Mergner, T., Hlavacka, F. & Schweigart, G. (1993) Interaction of vestibular and proprioceptive inputs. J. Vest. Res., 3:41-57.
• Mergner, T., Huber, W. & Becker, W. (1997) Vestibular-neck interaction and transformations of sensory coordinates. J. Vestib. Res., 7 (in press).
• Mergner, T., Rottler, G., Kimmig, H. & Becker, W. (1992) Role of vestibular and neck inputs for the perception of object motion in space. Exp. Brain Res., 89:655-668.
• Mergner, T., Siebold, C., Schweigart, G. & Becker, W. (1991) Human perception of horizontal head and trunk rotation in space during vestibular and neck stimulation. Exp. Brain Res., 85:389-404.
• Nashner, L.M. & Wolfson, P. (1974) Influence of head position and proprioceptive cues on short latency postural reflexes evoked by galvanic stimulation of the human labyrinth. Brain Res., 67:86-8.
• Peterka, R.J. & Benolken, M.S. (1995) Role of somatosensory and vestibular cues in attenuating visually induced human postural sway. Exp. Brain Res. 105:101-10.
• Roberts, T.D.M. (1978) Neurophysiology of Postural Mechanism (2nd ed.), London: Butterworths.
• Roberts, T.D.M. (1995) Understanding Balance: The Mechanics of Posture and Locomotion. Chapman & Hall.
• Roberts, T.D.M. (1996) Precis of: Understanding Balance: The Mechanics of Posture and Locomotion. PSYCOLOQUY 7(2) posture-locomotion.1.roberts.
• Tokita, T., Ito, Y. & Takagi, K. (1989) Modulation by head and trunk positions of the vestibulo-spinal reflexes evoked by galvanic stimulation of the labyrinth. Observations by labyrinthine evoked EMG. Acta Otololaryngol. (Stockholm)
• von Holst, E. & Mittelstaedt, H. (1950) Das Reafferenzprinzip (Wechselwirkungen zwischen Zetralnervensystem und Peripherie). Naturwissenschaften, 37:464-476.
• FIGURES
• FIGURE 1A:
• ------- | | | @ | @= VEST | | | - v - <--- (b) ----- | ---- \ v / \ | / \ v / \ | / \ v / \| / |v | || O| O= COM / v ^ \ / | | \ / v ^ \ | | | | | v ^ | | | | | | v ^ | | | | | | v ^ | | | | | | v ^ | | | | | |v ^| || || |v ^| - <--- (a) | | | | -v-^--- MMMMMMMMMMMMMMMMMMMMMMMM
• FIGURE 1B:
• VEST.(lambda) ............. . space . . reference . . . ............. | ^ hs|(lambda HS) | | |hs` lambda ht v+ ht |+ --->0 --->0 -| ^+ | | | ts | ts` lambda tl v+ tl |+ --->0 --->0 -| ^+ | | | ls | ls` lambda lf v+ lf |+ --->0 --->0 -| ^+ | | | fs | fs` | | | ---------------------------- | | | ............. | | | | foot . space . | | --->|support re. reference . |----- | . . | | ............. | ----------------------------
• FIGURE 1C:
• PHYSICS . SENSORY AND . CENTRAL PROCESSING .,,,,,,,,,,,,, --------------., Neural ,<----------------- | ., Controller, | | .,,,,,,,,,,,,, | | . | | bio- D I R E C T L O O P | | mecha- . | ext. | nics . ,,|,,, torque v- .,,,,,,,,,,,,, ,+|II, BODY re-->O----.-- ----->, Leg ,--->O------.----->O , FOOT + | BrF ., Prop , ^ | ,+^ , | .,,,,,,,,,,,,, | | ,,|,,, | . Vibrat. | | | . | | | . | | | . | | displacem. V(+) . ,,|,,,, | FOOT ,,,,,,,, BrS.,,,,,,,,,,,,, , v(-), | Supp. ----->,COORD ,---->, Vest ,--->O----->O------ re ,TRANSF, ., System , ^ ,+ I , SPACE ,,,,,,,, .,,,,,,,,,,,,, | ,,,,,,, . Galv. .
• FIGURE LEGEND
• Figures 1A, 1B: Conceptual model of vestibular-proprioceptive interaction for postural stabilization. The down- and up-transformation hypothesis is depicted for a standing subject literally (1A) and in the form of a signal flow diagram (1B; VEST., vestibular system; COM, center of body mass; lambda, vestibular transfer characteristics; HS, head-in-space velocity; hs, ht, ts, tl, lf, ls, and fs, internal velocity signals of head-in- space, head-to-trunk, trunk-in-space, trunk-to-leg, leg- to-foot, leg-in-space, and foot-in-space, respectively).
• Figure 1C: Depiction of the concept in terms of a wiring diagram for a condition in which the subject stabilizes body posture by applying muscle torque across the ankle joints. I, down-transformation. II, up-transformation. For details, see text.