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Cerebral Cortex Advance Access published online on September 10, 2009
Cerebral Cortex, doi:10.1093/cercor/bhp185
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© 2009 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Effects of Aging on Paired-Pulse Behavior of Rat Somatosensory Cortical Neurons

Marianne David-Jürgens and Hubert R. Dinse

Institute for Neuroinformatics, Department of Theoretical Biology, Neural Plasticity Laboratory, Ruhr-University Bochum, D-44780 Bochum, Germany

Address correspondence to Marianne David-Jürgens. Email: Marianne.David{at}neuroinformatik.rub.de.

Aging affects all levels of neural processing including changes of intracortical inhibition and cortical excitability. The paired-pulse stimulation protocol, the application of 2 stimuli in close succession, is used to investigate cortical excitability. The paired-pulse behavior is characterized by the fact that the second response is significantly suppressed at short interstimulus intervals (ISIs) but approaches the first response with increasing ISIs. However, there are controversial reports about the influence of age on paired-pulse behavior. We therefore used pairs of tactile stimuli (ISIs from tens to hundreds of milliseconds) to record extracellular responses of somatosensory cortical neurons of young and aged rats. Paired-pulse behavior was quantified as the ratio of the amplitude of the second response divided by the first. For all ISIs, we found significantly higher ratios in the old animals indicating reduced paired-pulse suppression (PPS). Evaluation of the single response components revealed a significant reduction of the response to the first stimulus for old animals but no age-dependent decrement to the second. Changes in PPS are usually mediated by modulating the second response characteristics. Thus, our data demonstrate reduced PPS due to an overall reduction of the first response as a form of modified PPS developing at old age.

Key Words: aging • cortical excitability • intracortical inhibition • rat • somatosensory cortex


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