A prominent feature of thalamocortical circuitry in sensory systems is the extensive and highly organized feedback projection from the cortex to thalamic neurons that provide input to it. Intriguingly, many corticothalamic (CT) neurons are weakly responsive to peripheral stimuli, or silent altogether. Here using the whisker-to-barrel system, we examine whether the responses of CT neurons and their related thalamic neurons are affected by motor cortex, a prominent source of input to deep layers of the somatosensory cortex. Pharmacological facilitation of motor cortex activity produced using focal, microiontophoresis leads to enhanced whisker-evoked firing of topographically aligned layer 6 neurons, including identified CT cells, and of cells in corresponding regions of the thalamic ventral posterior medial nucleus (VPm barreloids). Together, the findings raise the possibility that cortico-thalamo-cortical circuitry in primary sensory areas is engaged by other functionally related cortical centers, providing a means for context-dependent regulation of information processing within thalamocortical circuits.
We investigated how vMCx influence activity in thalamic VPm nucleus in a freely behaving rat. We examine afferent-evoked thalamic activity in animals that are either alert but voluntarily relatively motionless or actively whisking in the air without object contact. Afferent activity is evoked in VPm by means of electrical microstimulation of a single whisker follicle. In some experiments, neural processing in brainstem trigeminal nuclei was either by-passed by means of medial lemniscus stimulation, or altered by pharmacological intervention. We found that sensory responses during voluntary whisker movements, when motor cortex is likely to be active, are reduced relative to responses that occur during periods of wakeful quiescence. Enhancement of thalamic activity during whisking can be observed, however, when signal processing in sub-thalamic centers is either by-passed or experimentally altered. Findings suggest that during voluntary movement activity within the lemniscal system is globally diminished, perhaps at early, brainstem levels at the same time that activity within specific thalamocortical neuronal populations is facilitated. Though activity levels are reduced system-wide, activity within some local circuits may be subject to less net suppression. This decrease in suppression may occur on a moment-to-moment basis in a context-dependent manner. Thus, during voluntary whisker movement, sensory transmission in thalamocortical circuits may be modulated according to specific activation patterns distributed across the motor map.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-12182007-021405 |
| Date | 19 December 2007 |
| Creators | Lee, SooHyun |
| Contributors | George E. Carvell, Asaf Keller, Peter L. Strick, Karl Kandler, Neeraj J. Gandhi, Daniel J. Simons |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-12182007-021405/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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