Review
Plasticity and stability of somatosensory maps in thalamus and cortex

https://doi.org/10.1016/S0959-4388(00)00112-4Get rights and content

Abstract

Work on elucidating the mechanisms of plasticity in somatosensory maps continues apace. Recent work has focused on both the nature of the thalamocortical interactions that determine plasticity, and on the differences between plasticity induced by nerve block or damage versus that induced by experience. Recordings from awake behaving animals have thrown light on the thalamocortical circuit mechanisms that underlie map plasticity; meanwhile, intracellular recordings from cortical slices have thrown light on the precise synaptic mechanisms underlying plasticity.

Introduction

Somatosensory maps are often studied both as a means of understanding how information is processed between cortical columns and as a means of measuring plasticity. The monkey hand representation (in the primary somatosensory cortex) and the rat whisker representation (in the barrel cortex) have received much attention in recent years. Both contain unitary representations of body locations: digits in the first case and whiskers in the second. The mapping of adjacent body areas presumably confers some computational advantage on the system, and yet the map is plastic enough to alter these relationships in response to changes in sensory experience or to nerve damage.

In this review, we focus on a number of recent papers concerned with the somatosensory map and plasticity of the somatosensory system. Although lesion-induced plasticity differs in many respects from experience-dependent plasticity, and neonatal plasticity may differ from that found in the adult, we have tended to be inclusive in this review in order to cover work published during the past year. We have split the reports into three sections. The first section concerns plasticity of a single whisker’s cortical representation, assessed by intrinsic signal imaging. The second section covers recent results on the location of plasticity within the somatosensory neuraxis, as assessed by single- and multi-electrode recording. In the third section, we review evidence on some of the cellular mechanisms that might underlie map plasticity in the cortex, such as coincidence detection of presynaptic and postsynaptic action potentials (or spikes).

Section snippets

Functional imaging of whisker representation

It has previously been found that stimulation of a single whisker elicits a response within the posterior medial barrel subfield that covers an area of approximately 2 mm2 as assessed with optical imaging of the intrinsic signal 1, 2. An area of 2 mm2 is roughly equivalent to the principal barrel-column for the stimulated whisker plus all of the surrounding barrels (8 or 9, depending on the location). This finding is consistent with the fact that neurones in the principal barrel-column plus all

The locus of sensory map plasticity

When changes in cortical somatosensory map representation were described in 1983 by Merzenich et al. [8] for adult animals, it was natural to assume that the changes described originated in the cortex. Subsequent work has shown that this certainly can be the case if plasticity is induced by changes in sensory experience. For example, a period of single-whisker experience leads to cortical expression of plasticity that depends on intracortical connections [9] but that is not accompanied by

Coincidence detection as a mechanism for map plasticity

Substantial progress has been made recently toward uncovering cellular mechanisms for experience-dependent plasticity in the barrel cortex [19••]. Experiments in two-week-old rat brain slices, using dual recordings from interconnected intrabarrel spiny stellate neurones, show that transmission between these neurones can be downregulated by pairing presynaptic and postsynaptic spike activity. Moreover, this form of LTD can be evoked only if presynaptic and postsynaptic spiking occur within a 10

Conclusions

The multiplicity of techniques being brought to bear on somatosensory cortex, from multi-electrode recording and intrinsic imaging through to dual intracellular recording in slices, is yielding a greater wealth of information on plasticity in this area than ever before. Recent studies on plasticity induced by nerve damage or nerve block show that the cortex is involved in changing subcortical representations. The exact nature of the thalamocortical interaction will need to be studied further in

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

  • • of special interest

  • •• of outstanding interest

References (21)

  • D.B. Polley et al.

    Two directions of plasticity in the sensory-deprived adult cortex

    Neuron

    (1999)
  • M.M. Merzenich et al.

    Topographic reorganization of somatosensory cortical areas 3b and 1 in adult monkeys following restricted deafferentation

    Neuroscience

    (1983)
  • S.A. Masino et al.

    Quantitative long-term imaging of the functional representation of a whisker in the rat barrel cortex

    Proc Natl Acad Sci USA

    (1996)
  • R. Bhavin et al.

    Temporal modulation of spatial borders in rat barrel cortex

    J Neurophysiol

    (1998)
  • M. Armstrong-James et al.

    Spatiotemporal convergence and divergence in rat SI ‘barrel’ cortex

    J Comp Neurol

    (1987)
  • S. Glazewski et al.

    The time course of experience-dependent synaptic potentiation and depression in barrel cortex of adolescent rats

    J Neurophysiol

    (1996)
  • M. Kossut et al.

    Single vibrissal cortical column in SI cortex of rats and its alterations in neonatal and adult vibrissa-deafferented animals: a quantitative 2DG study

    J Neurosci

    (1988)
  • S. Glazewski et al.

    Experience-dependent depression of vibrissae responses in rat barrel cortex

    Eur J Neurosci

    (1998)
  • K. Fox

    The cortical component of experience-dependent synaptic plasticity in the barrel cortex

    J Neurosci

    (1994)
  • H. Wallace et al.

    Local cortical interactions determine the form of cortical plasticity

    J Neurobiol

    (1999)
There are more references available in the full text version of this article.

Cited by (42)

  • Hebbian and Homeostatic Plasticity Mechanisms in Regular Spiking and Intrinsic Bursting Cells of Cortical Layer 5

    2015, Neuron
    Citation Excerpt :

    The cerebral cortex shows a remarkable capacity for functional plasticity (Feldman, 2009; Fox et al., 2000; Fox and Wong, 2005).

  • Tactile representation in somatosensory thalamus (VPL) and cortex (S1) of awake primate and the plasticity induced by VPL neuroprosthetic stimulation

    2015, Brain Research
    Citation Excerpt :

    For instance, cortical synaptic proliferation was observed after four days of VPL stimulation (Keller et al., 1992a). Thus, where plasticity is initiated is still controversial (Kaas, 1999; Fox et al., 2000). Additionally, there are no adequate data showing how it affects sensory encoding and whether or not it is suitable for somatosensory prosthetic application.

  • Sensitive and critical periods during neurotypical and aberrant neurodevelopment: A framework for neurodevelopmental disorders

    2015, Neuroscience and Biobehavioral Reviews
    Citation Excerpt :

    Critical periods are limited during a specific time window and after their closure, the phenotype is classically thought not to be malleable – but see, e.g. (Oberlaender et al., 2012; Pizzorusso et al., 2002) for somatosensory and visual manipulations in adulthood. The distinction between critical and sensitive periods can be subtle: Historically, critical periods have been used to describe brain circuit-based phenotypes including ocular dominance in the visual system or synaptic plasticity in the developing somatosensory cortex (Fox et al., 2000; Hensch, 2004). Sensitive periods, on the other hand, are often referred to as time windows during which exposure of the organism to external factors or experience modulates the emergence of specific behaviours.

  • Animal Models of Focal Dystonia

    2015, Movement Disorders: Genetics and Models: Second Edition
View all citing articles on Scopus
View full text