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The Journal of Neuroscience, January 1, 1998, 18(1):548-558

A Focal Zone of Thalamic Plasticity

Jayson L. Parker^{1, 3}, Michael L. Wood², and Jonathan O. Dostrovsky¹

Departments of ¹ Physiology and ² Medical Imaging, University of Toronto, Toronto, Ontario, Canada M5S-1A8, and ³ Cognitive Neurology Unit, Sunnybrook Hospital, Toronto, Ontario, Canada M4N-3M5

In this study, sensory maps in the thalamus were investigated by examining their volume and shape. We determined the forelimb representation in adult rats after the removal of hindlimb input by nucleus gracilis lesions. Three-dimensional reconstructions of thalamic sensory maps were obtained from a grid of electrode penetrations. We found that the volume of the shoulder sensory map contracted >50% at an acute time interval (n = 6), followed by a robust volumetric sensory map expansion of 25% at 1 week (n = 8) and 1 month (n = 8) after lesion relative to controls (n = 8). The topology of the volumetric increase was scrutinized by slicing functional maps in the coronal, sagittal, and horizontal planes. The equivalence of such slices from each animal was established by virtue of their distance from either a functional or neuroanatomical landmark. Surprisingly, all of the volumetric increase unequivocally occurred in a circumscribed coronal slice 300 µm thick. This focal zone was located toward the rostral pole of the thalamic tactile relay, the ventroposterolateral nucleus. Analysis in the sagittal plane revealed that, unexpectedly, the shoulder map volume expanded by superimposing its representation on that of the forepaw, via an advancement of the shoulder representation by 0.6 mm medially. We propose a "hot spot" hypothesis in which focal zones of plasticity may not be specific to the thalamus but may have manifestations elsewhere in the nervous system, such as the cerebral cortex or dorsal column nuclei.

Key words: hot spot; plasticity; thalamus; receptive field; VPL; somatotopy; lemniscal; nucleus gracilis; visualization; topographic overlap; focal zone

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Copyright © 1998 Society for Neuroscience  0270-6474/98/181548-11$05.00/0

This article has been cited by other articles:

				T. M. Woods, C. G. Cusick, T. P. Pons, E. Taub, and E. G. Jones Progressive Transneuronal Changes in the Brainstem and Thalamus after Long-Term Dorsal Rhizotomies in Adult Macaque Monkeys J. Neurosci., May 15, 2000; 20(10): 3884 - 3899. [Abstract] [Full Text] [PDF]

				J. L. Parker and J. O. Dostrovsky Cortical Involvement in the Induction, But Not Expression, of Thalamic Plasticity J. Neurosci., October 1, 1999; 19(19): 8623 - 8629. [Abstract] [Full Text] [PDF]

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