Articles

Cortical theta is increased while thalamocortical coherence is decreased in rat models of acute and chronic pain

LeBlanc, Brian W.¹; Lii, Theresa R.¹; Silverman, Andrew E.; Alleyne, Robert T.; Saab, Carl Y.^*

Department of Neurosurgery, Rhode Island Hospital, and Department of Neuroscience, Brown University, Providence, RI, USA

^* Corresponding author. Address: Department of Neurosurgery, Department of Neuroscience, Brown University, 593 Eddy Street, Aldrich 402, Providence, RI 02903, USA. Tel.: +1 (401) 444 4290; fax: +1 (401) 444 8052.

E-mail address:[email protected]

¹ Brian W. LeBlanc and Theresa R. Lii contributed equally to this work.

Article history:

Received 22 October 2013

Received in revised form 8 January 2014

Accepted 14 January 2014

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.

Pain 155(4):p 773-782, April 2014. | DOI: 10.1016/j.pain.2014.01.013

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Abstract

Summary

Spontaneous pain in animals decreases thalamocortical coherence and increases cortical theta power.

Thalamocortical oscillations are critical for sensory perception. Although pain is known to disrupt synchrony in thalamocortical oscillations, evidence in the literature is controversial. Thalamocortical coherence has been reported to be increased in patients with neurogenic pain but decreased in a rat model of central pain. Moreover, theta (4 to 8 Hz) oscillations in primary somatosensory (S1) cortex are speculated to predict pain in humans. To date, the link between pain and network oscillations in animal models has been understudied. Thus, we tested the hypothesis that pain disrupts thalamocortical coherence and S1 theta power in two rat models of pain. We recorded electrocorticography (ECoG) waveforms over S1 and local field potentials (LFP) within ventral posterolateral thalamus in freely behaving rats under spontaneous (stimulus-independent) pain conditions. Rats received intradermal capsaicin injection (Cap) in the hindpaw, followed hours later by chronic constriction injury (CCI) of the sciatic nerve lasting several days. Our results show that pain decreases coherence between LFP and ECoG waveforms in the 2- to 30-Hz range, and increases ECoG power in the theta range. These changes are short-lasting after Cap and longer-lasting after CCI. These data might be particularly relevant to preclinical correlates of spontaneous pain-like behavior, with potential implications to clinical biomarkers of ongoing pain.