J.
Neurosci. Table of Contents for 8 September 2004; Vol. 24, No. 36
Ipsilateral Actions of Feline Corticospinal
Tract Neurons on Limb
Motoneurons
S. A. Edgley, E. Jankowska, and
I. Hammar
Contralateral pyramidal tract (PT) neurons
arising in the primary motor cortex are the major route through which
volitional limb movements are controlled. However, the contralateral
hemiparesis that follows PT neuron injury on one side may be counteracted by
ipsilateral of actions of PT neurons from the undamaged side. To investigate
the spinal relays through which PT neurons may influence ipsilateral
motoneurons, we analyzed the synaptic actions evoked by stimulation of the
ipsilateral pyramid on hindlimb motoneurons after transecting the descending
fibers of the contralateral PT at a low thoracic level. The results show that
ipsilateral PT neurons can affect limb motoneurons trisynaptically by
activating contralaterally descending reticulospinal neurons, which in turn
activate spinal commissural interneurons that project back across to
motoneurons ipsilateral to the stimulated pyramidal tract. Stimulation of the
pyramids alone did not evoke synaptic actions in motoneurons but potently
facilitated disynaptic EPSPs and IPSPs evoked by stimulation of reticulospinal
tract fibers in the medial longitudinal fascicle. In parallel with this
double-crossed pathway, corticospinal neurons could also evoke ipsilateral actions
via ipsilateral descending reticulospinal tract fibers, acting through
ipsilaterally located spinal interneurons. Because the actions mediated by
commissural interneurons were found to be stronger than those of ipsilateral
premotor interneurons, the study leads to the conclusion that ipsilateral
actions of corticospinal neurons via commissural interneurons may provide a
better opportunity for recovery of function in hemiparesis produced by
corticospinal tract injury.
J. Neurosci. Table of Contents for 15 September
2004; Vol. 24, No. 37
Is Interlimb Transfer of Force-Field Adaptation
a Cognitive Response to the
Sudden Introduction of Load?
Nicole Malfait and David J. Ostry
Recently, Criscimagna-Hemminger et al. (2003)
reported a pattern of generalization of force-field adaptation between arms
that differs from the pattern that occurs across different configurations of
the same arm. Although the intralimb pattern of generalization points to an
intrinsic encoding of dynamics, the interlimb transfer described by these
authors indicates that information about force is represented in a frame of
reference external to the body. In one condition, the field was introduced
suddenly and produced clear deviations in hand paths; in the second condition,
the field was introduced gradually so that at no point during the adaptation
process could subjects observe or did they have to correct for a substantial
kinematic error. In the first case, a pattern of interlimb transfer consistent
with Criscimagna-Hemminger et al. (2003) was observed, whereas no transfer of
learning between limbs occurred in the second condition. The findings suggest
that there is limited transfer of fine compensatory-force adjustment between
limbs. Transfer, when it does occur, may be primarily the result of a cognitive
strategy that arises as a result of the sudden introduction of load and
associated kinematic error.
PLoS
Biology:
PLoS
Biology Vol 2 Issue 9 Sept 2004 – nothing
J
Motor Behav
J Mot Behav. 2004 Sep;36(3):291-304.
First-trial adaptation to prism exposure: artifact of visual
capture.
Redding GM, Wallace B.
Department of Psychology, Illinois
State University, IL, USA. gredding@ilstu.edu
Terminal target-pointing error on
the 1st trial of exposure to optical displacement is usually less than is
expected from the optical displacement magnitude. The authors confirmed
1st-trial adaptation in the task of pointing toward optically displaced targets
while visual feedback was delayed until movement completion. Measurement of
head-shoulder posture while participants (N = 24) viewed the optically
displaced field revealed that their shoulders felt turned in the direction
opposite to the displacement (visual capture), accounting for all but about 4%
to 10% of 1st-trial adaptation. First-trial adaptation was unrelated to
realignment aftereffects. First-trial adaptation is largely an artifact of the
asymmetry of the structured visual field produced by optical displacement,
which induces a felt body rotation, thereby reducing the effective optical
displacement.