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The Journal of Neuroscience, May 14, 2008, 28(20):5169-5177; doi:10.1523/JNEUROSCI.0490-08.2008

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Behavioral/Systems/Cognitive
Vibrissal Responses of Thalamic Cells That Project to the Septal Columns of the Barrel Cortex and to the Second Somatosensory Area

Hajnalka Bokor,^1,2 László Acsády,¹ and Martin Deschênes²

¹Institute of Experimental Medicine, National Academy of Sciences, H-1450 Budapest, Hungary, and ²Centre de Recherche Université Laval Robert-Giffard, Laval University, Québec City, Québec, Canada G1J 2G3

Correspondence should be addressed to Dr. Martin Deschênes, Centre de Recherche Université Laval Robert-Giffard, 2601 de la Canardière, Québec City, Québec, Canada G1J 2G3. Email: martin.deschenes{at}crulrg.ulaval.ca

The rodent somatosensory cortex contains barrel-related and septa-related circuits representing two separate streams of vibrissa information processing that differ in their response patterns and anatomical connections. Whereas barrel-related circuits process lemniscal inputs that transit through the thalamic barreloids, septa-related circuits process paralemniscal inputs and inputs that are relayed through the ventral lateral part of the ventral posterior medial nucleus (VPMvl). Septa-projecting thalamic afferents also target the secondary somatosensory cortical area. Although a number of studies have examined response properties in the lemniscal pathway, and demonstrated that barreloids receive feedback from specific sets of corticothalamic and reticular thalamic neurons, such information is currently lacking for the VPMvl. In the present study, we show that in sharp contrast to the relay cells of the barreloids VPMvl neurons exhibit large multiwhisker receptive fields that are independent of input from the principal trigeminal nucleus. Results also suggest that the topography of receptive fields and response properties in VPMvl rely on converging input from neurons of the interpolaris trigeminal nucleus. Tracer injection and single-cell labeling further reveal that the VPMvl receives input from specific populations of reticular thalamic and corticothalamic neurons. Together, these results confirm the status of the VPMvl as a thalamic relay of an independent parallel pathway of vibrissa information processing. They further indicate that a sensory pathway does not merely consist on a three-neuron chain that links the vibrissae to the cerebral cortex, but that it also involves specific sets of topographically related corticothalamic and reticular thalamic projections.

Key words: vibrissa; barrel cortex; trigeminal nuclei; ventral posterior medial nucleus; thalamus; second somatosensory area

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Received Feb. 3, 2008; revised March 10, 2008; accepted March 11, 2008.

Correspondence should be addressed to Dr. Martin Deschênes, Centre de Recherche Université Laval Robert-Giffard, 2601 de la Canardière, Québec City, Québec, Canada G1J 2G3. Email: martin.deschenes{at}crulrg.ulaval.ca

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