Volume 17, Number 23,
Issue of December 1, 1997
pp. 9220-9232
Differential Effects of Abnormal Tactile Experience on Shaping
Representation Patterns in Developing and Adult Motor Cortex
Received July 22, 1997; revised Sept. 22, 1997; accepted Sept. 22, 1997.
George W. Huntley
Fishberg Research Center for Neurobiology, The Mount Sinai School
of Medicine, New York, New York 10029-6574
This study investigates the influence of early somatosensory
experience on shaping movement representation patterns in motor cortex.
Electrical microstimulation was used to map bilaterally the motor
cortices of adult rats subjected to altered tactile experience by
unilateral vibrissa trimming from birth (birth-trimmed group) or for
comparable periods that began in adulthood (adult-trimmed group).
Findings demonstrated that (1) vibrissa trimming from birth, but not
when initiated in adulthood, led to a significantly smaller-sized
primary motor cortex (M1) vibrissa representation in the hemisphere
contralateral to the trimmed vibrissae, with no evidence for
concomitant changes in size of the adjacent forelimb representation or
the representation of the intact vibrissae in the opposite
(ipsilateral) hemisphere; (2) in the contralateral hemispheres of the
birth-trimmed group, an abnormal pattern of evoked vibrissa movement
was evident in which bilateral or ipsilateral (intact) vibrissa
movement predominated; (3) in both hemispheres of the birth-trimmed
group, current thresholds for eliciting movement of the trimmed
vibrissa were significantly lower than normal; and (4) in the
adult-trimmed group, but not in the birth-trimmed group, there was a
decrease bilaterally in the relative frequency of dual
forelimb-vibrissa sites that form the common border between these
representations. These results show that sensory experience early in
life exerts a significant influence in sculpting motor representation
patterns in M1. The mature motor cortex is more resistant to the type
and magnitude of influence that tactile experience has on developing
M1, which may indicate that such an influence is constrained by a
developmentally regulated critical period.
Key words:
motor cortex;
rat;
vibrissa;
plasticity;
development;
intracortical microstimulation