Cortical Barrels: Maps and Plasticity

Abstract

The somatosensory cortex of rodents contains clusters of neurons called ‘barrels’ that are related in a one‐to‐one manner to individual mystacial vibrissae on the contralateral face. Signals from the sensory periphery influence the establishment of the system's distinctive anatomical organization during development and regulate the functional properties of cortical neurons throughout the animal's life.

Keywords: somatosensory; vibrissae; topography; tactile; neuronal circuits

Figure 1.

Anatomical basis for the ‘one barrel–one vibrissa’ hypothesis. Each peripheral axon in the trigeminal nerve innervates one whisker follicle. Centrally the axons are aggregated in whisker‐related bundles that terminate in several nuclei in the brainstem. Illustrated from top to bottom these are: principal sensory nucleus and spinal trigeminal complex subnuclei oralis, interpolaris and caudalis. Barrelettes are present in all but the subnucleus oralis. Whisker‐related aggregations of afferent fibres and cell bodies are also observed in the contralateral thalamus and cerebral cortex. Inset: Cauterization of the middle row of whiskers on the day of birth (postnatal day (PND) 0) leads to an abnormal cortical barrel field.

Figure 2.

Information processing in the whisker–barrel cortex. Each thalamic barreloid conveys multi‐whisker information (indicated by colour mixture) to its corresponding cortical barrel where neuronal responses become focused on the barrel's principal whisker (denoted by solid colours). By means of horizontal connections linking neighbouring barrel‐associated columns, single‐whisker information leaving the barrel is combined in supragranular and infragranular layers, creating spatially and temporally complex receptive fields. Supragranular (layer II/III) intercolumnar connections into the central (green) barrel–column are denoted by the horizontal blue and yellow arrows; connections involving the infragranular layers are not shown. Barrels are only sparsely interconnected, indicated by the absence of connecting arrows in layer IV, although neurons in other layers do provide some inputs to them.

Figure 3.

Effects of whisker trimming on cortical receptive fields. In normally reared adult animals, several days of whisker cutting (in this case, of the whisker associated with the yellow barrel in Figure ) leads to a loss of responsiveness in the corresponding barrel and increased responsiveness to the remaining whiskers in the barrels corresponding to neighbouring, intact (nontrimmed) whiskers. Note that neurons in the latter now respond less selectively to green versus blue whiskers (compare with Figure ), possibly as a result of strengthened intercolumnar connections in the supragranular layers. With neonatal whisker trimming followed by regrowth in adulthood of the yellow whisker, neurons in the yellow barrel also become highly responsive to the yellow whisker and to previously trimmed (e.g. green) and nontrimmed whiskers (not shown). These effects, which remain even after months of regrowth, may reflect alterations in barrel circuitry whereby neuronal receptive fields more closely mimic those of the thalamic barreloid neurons.

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References

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Further Reading

Jones EG and Diamond IT (1995) Cerebral Cortex, vol. 11: The Barrel Cortex of Rodents. New York: Plenum Press.

Kandel ER, Schwartz JH and Jessel TM (2000) Touch. In: Principles of Neuroscience, 4th edn, pp. 451–471. New York: McGraw‐Hill.

Killackey HP (1980) Pattern formation in the trigeminal system of the rat. Trends in Neurosciences 3: 303–305.

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White EL (1989) Cortical Circuits: Synaptic Organization of the Cerbral Cortex – Structure, Function and Theory. Boston: Birkhauser.

Woolsey TA (1978) Some anatomical bases of cortical somatotopic organization. Brain, Behavior and Evolution 15: 325–371.

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How to Cite close
Simons, Daniel J, and Land, Peter W(May 2003) Cortical Barrels: Maps and Plasticity. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0000083]