Stimulus Frequency Processing in Awake Rat Barrel Cortex

Abstract

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 Յ9 apps, cortical neurons responded with one to two spikes per stimulus, whereas at Ͼ9 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 Ͼ9 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.

Pathway-Specific Variations in Neurovascular and Neurometabolic Coupling in Rat Primary Somatosensory Cortex

“…IO stimulation at high intensity (20 and 30 Hz) resulted in no detectable activation of cortical neurons using c-Fos as a marker, a finding that correlated with the absence of tpO 2 dip and LFP responses, and the IO stimulation plots of synaptic activity with CBF and CMRO 2 displaying bell-shaped curves with very low responses at 30 Hz. They also agree with the reported decrement in the spiking rate of layers III and IV barrel neurons with increased stimulus frequency (Melzer et al, 2006). Our findings can well be explained by the frequency-dependent adaptation of cortical neurons, which occurs rapidly such that above 1 Hz, many cortical neurons cease firing after the first few deflections (Melzer et al, 2006).…”

Biomechanics of the Vibrissa Motor Plant in Rat: Rhythmic Whisking Consists of Triphasic Neuromuscular Activity

“…As such, this procedure has enabled other difficult behavioral tasks (Gao et al, 2001;Bermejo et al, 2002;Gao et al, 2003b;Friedman et al, 2006) and intracellular (Crochet and Petersen, 2006) and extracellular (Sachdev et al, 2000;Kleinfeld et al, 2002;Melzer et al, 2006) recording studies. Yet it has been heretofore undocumented how head restraint may alter whisking behavior.…”

State Changes Rapidly Modulate Cortical Neuronal Responsiveness

“…During natural exploration and behavior, rodent whiskers often receive prolonged stimulation (Prigg et al, 2002;Knutsen et al, 2006), and the response properties of somatosensory cortical neurons to such stimulation are markedly different from those associated with brief, punctuate stimuli (Armstrong-James and Fox, 1987;Kleinfeld et al, 2002;Arabzadeh et al, 2004;Knutsen et al, 2006;Melzer et al, 2006). When we examined the effects of changes in cortical network activity on responses to continuous whisker stimulation, we found that cortical networks continued to alternate between Up-like states (i.e., periods of increased multiple-unit activity simultaneous with tonic intracellular depolarization and lasting 200 -1000 ms) and Down-like states (i.e., periods of decreased multiple-unit activity with tonic intracellular hyperpolarization) (supplemental Fig.…”