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The Journal of Neuroscience, November 22, 2006, 26(47):12198-12205; doi:10.1523/JNEUROSCI.2620-06.2006
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Behavioral/Systems/Cognitive
Stimulus Frequency Processing in Awake Rat Barrel Cortex
Peter Melzer, Robert N. S. Sachdev, Ned Jenkinson, andFord F. Ebner Department of Psychology, Vanderbilt University, Nashville, Tennessee 37203
Correspondence should be addressed to Peter Melzer, Department of Psychology, Vanderbilt University, 301 Wilson Hall, 111 21st Avenue South, Nashville, TN 37203. Email: peter.melzer{at}vanderbilt.edu
In awake rats, we examined the relationship between neural spiking activity in primary somatic sensory cortex and the frequency of whisker stimulation. Neural responses were recorded extracellularly in barrel cortex while single whiskers were deflected with 0.5–18 air puffs per second (apps), a range that includes the whisk rates observed when rats explore their environment and discriminate surfaces with their whiskers. Twenty-nine neurons in layers III and IV were isolated in three rats (23 in barrel columns and 6 in septum columns). At
9 apps, cortical neurons responded with one to two spikes per stimulus, whereas at >9 apps, the response efficacy was reduced to only 0.2–0.4 spikes per stimulus. Several mechanisms are discussed that could account for the decrement in responsiveness. Despite this adaptation, neural spike rates increased in direct proportion with stimulus frequency when cast on logarithmic scales. At >9 apps, however, this relationship deteriorated in barrel columns in which the response approximately halved. In contrast, septum column cells continued to increase their spike rates linearly up to 18 apps, although they responded at lower magnitude than the barrel column cells. Our findings suggest that septum column neurons are potential candidates to encode stimulus frequency using spike rate across the entire frequency range relevant to rats' whisking behavior.
Key words: depression; excitation; inhibition; vibrissa; rat; somatosensory cortex
Received June 21, 2006; revised Sept. 21, 2006; accepted Oct. 11, 2006.
Correspondence should be addressed to Peter Melzer, Department of Psychology, Vanderbilt University, 301 Wilson Hall, 111 21st Avenue South, Nashville, TN 37203. Email: peter.melzer{at}vanderbilt.edu
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