Movement Systems: BBS Special Call for Commentators

Stevan Harnad harnad at phoenix.princeton.edu
Fri Jan 10 12:42:46 EST 1992


Below are the abstracts of 8 forthcoming target articles for a special
issue on Movement Systems that will appear in Behavioral and Brain
Sciences (BBS), an international, interdisciplinary journal that
provides Open Peer Commentary on important and controversial current
research in the biobehavioral and cognitive sciences. This will be the
first in a new series called "Controversies in Neuroscience,"
undertaken in collaboration with Paul Cordo and the RS Dow Neurological
Science Institute.

Commentators must be current BBS Associates or nominated by a current
BBS Associate. To be considered as a commentator on any of these
articles, to suggest other appropriate commentators, or for information
about how to become a BBS Associate, please send email to:

harnad at clarity.princeton.edu  or harnad at pucc.bitnet        or write to:
BBS, 20 Nassau Street, #240, Princeton NJ 08542  [tel: 609-921-7771]

Please specify which article or articles you would like to comment on.
(Commentators will be allotted 1000 words to comment on one of the
articles, 750 words more to comment on two of them, 500 more for three
and then 250 more for each additional one, for a maximum of 3500 words
to comment on all eight target articles.)

To help us put together a balanced list of commentators, please give
some indication of the aspects of the topic on which you would bring
your areas of expertise to bear if you were selected as a commentator.
In the next week or so, electronic drafts of the full text of each
article will be available for inspection by anonymous ftp according to
the instructions that follow after the abstracts. These drafts are for
inspection only; please do not prepare a commentary until you are
formally invited to do so.

____________________________________________________________________

1.  Alexander GE, MR De Long, & MD Crutcher:  DO CORTICAL AND BASAL
    GANGLIONIC MOTOR AREAS USE "MOTOR PROGRAMS" TO CONTROL MOVEMENT?
    bbs.alexander

2.  Bizzi E, N Hogan, FA Mussa-Ivaldi & S Giszter:  DOES THE NERVOUS
    SYSTEM USE EQUILIBRIUM-POINT CONTROL TO GUIDE SINGLE AND MULTIPLE
    JOINT MOVEMENTS? bbs.bizzi

3.  Bloedel JR:  DOES THE ONE-STRUCTURE/ONE-FUNCTION RULE APPLY TO THE
    CEREBELLUM? bbs.bloedel

4.  Fetz EH:  ARE MOVEMENT PARAMETERS RECOGNIZABLY CODED IN SINGLE
    NEURON ACTIVITY? bbs.fetz

5.  Gandevia SC & D Burke:  DOES THE NERVOUS SYSTEM DEPEND ON
    KINESTHETIC INFORMATION TO CONTROL NATURAL LIMB MOVEMENTS?
    bbs.gandevia

6.  McCrea DA:  CAN SENSE BE MADE OF SPINAL INTERNEURON CIRCUITS?
    bbs.mccrea

7.  Robinson DA:  IMPLICATIONS OF NEURAL NETWORKS FOR HOW WE THINK
    ABOUT BRAIN FUNCTION bbs.robinson

8.  Stein JF:  POSTERIOR PARIETAL CORTEX AND EGOCENTRIC SPACE
    bbs.stein

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1. 	DO CORTICAL AND BASAL GANGLIONIC MOTOR AREAS
	USE "MOTOR PROGRAMS" TO CONTROL MOVEMENT?

	Garrett E. Alexander, Mahlon R. De Long, and Michael D. Crutcher
	Department of Neurology
	Emory University School of Medicine
	Atlanta, GA 30322
        gea at vax3200.neuro.emory.edu

KEYWORDS: basal ganglia, cortex, motor system, motor program, motor
control, parallel processing, connectionism, neural network

ABSTRACT: Prevailing engineering-inspired theories of motor control
based on sequential/algorithmic or motor programming models are
difficult to reconcile with what is known about the anatomy and
physiology of the motor areas. This is partly because of certain
problems with the theories themselves and partly because of features of
the cortical and basal ganglionic motor circuits that seem ill-suited
for most engineering analyses of motor control. Recent developments in
computational neuroscience offer more realistic connectionist models of
motor processing. The distributed, highly parallel, and nonalgorithmic
processes in these models are inherently self-organizing and hence more
plausible biologically than their more traditional algorithmic or
motor-programming counterparts. The newer models also have the
potential to explain some of the unique features of natural,
brain-based motor behavior and to avoid some of the computational
dilemmas asscociated with engineering approaches.

-------------------------------------------------------------------
2. 	DOES THE NERVOUS SYSTEM USE EQUILIBRIUM-POINT CONTROL
	TO GUIDE SINGLE AND MULTIPLE JOINT MOVEMENTS?

	E. Bizzi, N. Hogan, F.A. Mussa-Ivaldi and S. Giszter
	Department of Brain and Cognitive Sciences and
	Department of Mechanical Engineering
	Massachusetts Institute of Technology
	Cambridge, MA 02139
        emilio at wheaties.ai.mit.edu

KEYWORDS: spinal cord, force field, equilibrium point,
microstimulation, multi-joint coordination, contact tasks, robotics,
inverse dynamics, motor control.

ABSTRACT: The hypothesis that the central nervous system (CNS)
generates movement as a shift of the limb's equilibrium posture has
been corroborated experimentally in single- and multi-joint motions.
Posture may be controlled through the choice of muscle length tension
curves that set agonist-antagonist torque-angle curves determining an
equilibrium position for the limb and the stiffness about the joints.
Arm trajectories seem to be generated through a control signal defining
a series of equilibrium postures.

The equilibrium-point hypothesis drastically simplifies the requisite
computations for multijoint movements and mechanical interactions with
complex dynamic objects in the environment. Because the neuromuscular
system is springlike, the instantaneous difference between the arm's
actual position and the equilibrium position specified by the neural
activity can generate the requisite torques, avoiding the complex
"inverse dynamic" problem of computing the torques at the joints.

The hypothesis provides a simple unified description of posture and
movement as well as performance on contact control tasks, in which the
limb must exert force stably and do work on objects in the environment.
The latter is a surprisingly difficult problem, as robotic experience
has shown.

The prior evidence for the hypothesis came mainly from psychophysical
and behavioral experiments. Our recent work has shown that
microstimulation of the spinal cord's premotoneuronal network produces
leg movements to various positions in the frog's motor space. The
hypothesis can now be investigated in the neurophysiological machinery
of the spinal cord.

--------------------------------------------------------------------
3.  DOES THE ONE-STRUCTURE/ONE-FUNCTION RULE APPLY TO THE CEREBELLUM?

		James R. Bloedel
		Division of Neurobiology
		Barrow Neurological Institute
		Phoenix, AZ 

KEYWORDS: cerebellum; Purkinje cells; mossy fibres; movement;
proprioception; body image; kinesthesis; robotics; posture.

ABSTRACT: The premise explored in this target article is that the
function of the cerebellum can be best understood in terms of the
operation it performs across its structurally homogeneous subdivisions.
The functional heterogeneity sometimes ascribed to these different
regions reflects the many functions of the central targets receiving
the outputs of different cerebellar regions. Recent studies by
ourselves and others suggest that the functional unit of the cerebellum
is its sagittal zone. It is hypothesized that the climbing fiber system
produces a short-lasting modification in the gain of Purkinje cell
responses to its other principle afferent input, the mossy
fiber-granule cell-parallel fiber system. Because the climbing fiber
inputs to sagittally aligned Purkinje cells can be activated under
functionally specific conditions, they could select populations of
Purkinje neurons that were most highly modulated by the distributed
mossy fiber inputs responding to the same conditions. These operations
may be critical for the on-line integration of inputs representing
external target space with features of intended movement,
proprioceptive and kinesthetic cues, and body image.

-----------------------------------------------------------------
4.	ARE MOVEMENT PARAMETERS RECOGNIZABLY CODED
		IN SINGLE NEURON ACTIVITY?

		Eberhard E. Fetz
		Regional Primate Research Center
		University of Washington
		Seattle, WA 98195
                fetz at locke.hs.washington.edu

KEYWORDS: neural coding; representation; neural networks;
cross-correlation; movement parameters; parallel distributed processing

ABSTRACT: To investigate neural mechanisms of movement, physiologists
have analyzed the activity of task-related neurons in behaving animals.
The relative onset latencies of neural activity have been scrutinized
for evidence of a functional hierarchy of sequentially recruited
centers, but activity appears to change largely in parallel. Neurons
whose activity covaries with movement parameters have been sought for
evidence of explicit coding of parameters such as active force, limb
displacement and behavioral set. Neurons with recognizable relations to
the task are typically selected from a larger population, ignoring
unmodulated cells as well as cells whose activity is not related to the
task in a simple, easily recognized way. Selective interpretations are
also used to support the notion that different motor regions perform
different motor functions; again, current evidence suggests that units
with similar properties are widely distributed over different regions.

These coding issues are re-examined for premotoneuronal (PreM) cells,
whose correlational links with motoneurons are revealed by
spike-triggered averages. PreM cells are recruited over long times
relative to their target muscles. They show diverse response patterns
relative to the muscle force they produce; functionally disparate PreM
cells such as afferent fibers and descending corticomotoneuronal and
rubromotoneuronal cells can exhibit similar patterns. Neural mechanisms
have been further elucidated by neural network simulations of
sensorimotor behavior; the pre-output hidden units typically show
diverse responses relative to their targets. Thus, studies in which
both the activity and the connectivity of the same


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