J Psychiatry Neurosci 2014;39(4):232-38
Carmelo M. Vicario, PhD; Naeem Komeilipoor, MS; Paola Cesari, PhD; Robert D. Rafal, MD; Michael A. Nitsche, MD
Vicario — School of Psychology, The University of Queensland, St Lucia, Australia, and International School for Advanced Studies, Trieste, Italy; Komeilipoor, Cesari — Department of Neurological and Movement Sciences, University of Verona, Italy; Rafal — Wolfson Centre for Clinical and Cognitive Neuroscience, School of Psychology, Bangor University, Bangor, United Kingdom; Nitsche — Department of Clinical Neurophysiology, University of Göttingen, Göttingen, Germany
Background: Neuroimaging studies of chronic smokers report altered activity of several neural regions involved in the processing of rewarding outcomes. Neuroanatomical evidence suggests that these regions are directly connected to the tongue muscle through the corticobulbar pathways. Accordingly, we examined whether corticobulbar excitability might be considered a somatic marker for nicotine craving.
Methods: We compared motor-evoked potential (MEP) amplitudes recorded from the tongue and the extensor carpi radialis (control muscle) of chronic smokers under drug withdrawal and intake conditions as well as a nonsmoker group. All participants were tested during passive exposure to pictures showing a smoking cue or a meaningless stimulus. In the intake condition, chronic smokers were asked to smoke a real cigarette (CSn: group 1) or a placebo (CSp: group 2).
Results: Results show that MEP amplitudes recorded from the tongues of participants in the CSn and CSp groups under the withdrawal condition were selectively enhanced during exposure to a smoking cue. However, this effect on tongue MEP amplitudes disappeared in the intake condition for both the CSn and CSp groups.
Limitations: Limitations include the fact that the study was conducted in 2 different laboratories, the small sample size, the absence of data on chronic smoker craving strength and the different tastes of the real and placebo cigarettes.
Conclusion: These results suggest that, in chronic smokers, tongue muscle MEP amplitudes are sensitive to neural processes active under the physiological status of nicotine craving. This finding implicates a possible functional link between neural excitability of the corticobulbar pathway and the reward system in chronic smokers.
Submitted May 15, 2013; Revised Nov. 7, 2013; Accepted Nov. 27, 2013.
Competing interests: None declared.
Contributors: C.M. Vicario, P. Cesari, R.D. Rafal and M.A. Nietsche designed the study. C.M. Vicario and N. Komeilipoor acquired the data, which C.M. Vicario analyzed. All authors wrote and reviewed the article and approved the final version for publication.