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Open Access Highly Accessed Research

Ensemble encoding of nociceptive stimulus intensity in the rat medial and lateral pain systems

Yang Zhang1, Ning Wang2, Jin-Yan Wang2*, Jing-Yu Chang3, Donald J Woodward3 and Fei Luo12*

Author Affiliations

1 Neuroscience Research Institute and Department of Neurobiology, Peking University Health Science Center, Beijing, China

2 Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences, Beijing, China

3 Neuroscience Research Institute of North Carolina, Winston-Salem, NC, USA

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Molecular Pain 2011, 7:64  doi:10.1186/1744-8069-7-64

Published: 24 August 2011

Abstract

Background

The ability to encode noxious stimulus intensity is essential for the neural processing of pain perception. It is well accepted that the intensity information is transmitted within both sensory and affective pathways. However, it remains unclear what the encoding patterns are in the thalamocortical brain regions, and whether the dual pain systems share similar responsibility in intensity coding.

Results

Multichannel single-unit recordings were used to investigate the activity of individual neurons and neuronal ensembles in the rat brain following the application of noxious laser stimuli of increasing intensity to the hindpaw. Four brain regions were monitored, including two within the lateral sensory pain pathway, namely, the ventral posterior lateral thalamic nuclei and the primary somatosensory cortex, and two in the medial pathway, namely, the medial dorsal thalamic nuclei and the anterior cingulate cortex. Neuron number, firing rate, and ensemble spike count codings were examined in this study. Our results showed that the noxious laser stimulation evoked double-peak responses in all recorded brain regions. Significant correlations were found between the laser intensity and the number of responsive neurons, the firing rates, as well as the mass spike counts (MSCs). MSC coding was generally more efficient than the other two methods. Moreover, the coding capacities of neurons in the two pathways were comparable.

Conclusion

This study demonstrated the collective contribution of medial and lateral pathway neurons to the noxious intensity coding. Additionally, we provide evidence that ensemble spike count may be the most reliable method for coding pain intensity in the brain.

Keywords:
Laser; Intensity; Pain; Single unit; Ensemble encoding