The Journal of Neuroscience, June 1, 1998, 18(11):4403-4416
Single-Cell Correlates of a Representational Boundary in Rat
Somatosensory Cortex
Peter W.
Hickmott and
Michael M.
Merzenich
Keck Center for Integrative Neuroscience, University of California,
San Francisco, San Francisco, California 94143
In primary somatosensory cortex (S1), the transition from one
representation to the next is typically abrupt when assayed physiologically. However, the extent of anatomical projections to and
within the cortex do not strictly respect these physiologically defined
transitions. Physiological properties, such as synaptic strengths or
intracortical inhibition, have been hypothesized to account for the
functionally defined precision of these representational borders.
Because these representational borders can be translocated across the
cortex by manipulations or behaviors that change the activity patterns
of inputs to the cortex, understanding the physiological mechanisms
that delimit representations is also an important starting point for
understanding cortical plasticity.
A novel in vivo and in vitro preparation
has been developed to examine the cellular and synaptic mechanisms that
underlie representational borders in the rat. In vivo, a
short segment of the border between the forepaw-lower jaw
representations in rat S1 was mapped using standard
electrophysiological methods and was visibly marked using iontophoresis
of pontamine sky blue dye. Slices were then obtained from this marked
region and maintained in vitro. Intracellularly recorded
responses to electrical stimulation of supragranular cortex were
obtained from single neurons near the border in response to stimulation
within the representational zone or across the border. Both excitatory
and inhibitory responses were smaller when evoked by stimuli that
activated projections that crossed borders, as compared with stimuli to
projections that did not. These findings indicate that intracortical
network properties are contributing to the expressions of
representational discontinuities in the cortex.
Key words:
somatosensory cortex; representational boundary; horizontal connections; whole-cell recording; cortical slices; forepaw; lower jaw
Copyright © 1998 Society for Neuroscience 0270-6474/98/18114403-14$05.00/0
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