Conditioning of transcranial magnetic stimulation: Evidence of sensory-induced responding and prepulse inhibition
Received 28 March 2009; received in revised form 16 August 2009; accepted 17 August 2009. published online 18 September 2009.
Background
Transcranial magnetic stimulation (TMS) is a non-invasive method for stimulating the human cortex. Classical conditioning is a phenomenon of developed associations between stimuli. Our primary objective was to determine whether TMS effects could be conditioned. Prepulse inhibition represents another relationship between two stimuli, and a secondary assessment was performed to explore this relationship.
Methods
An auditory-visual conditioning stimulus (CS) was paired with the TMS unconditioned stimulus (US) over motor cortex producing a motor-evoked potential (MEP) unconditioned response (UR). Two versions of the CS-US pairing paradigms were tested, one with a short intertrial interval (ITI) and another with a long ITI. The short ITI paradigm had more CS-US pairings and shorter session duration than the long ITI paradigm. Tests for conditioned responses (CRs) were performed following CS-US pairing (CS+/US+), by presenting the CS alone (CS+/US−). Reverse testing was also performed after CS-US pairing (CS+/US+) in separate sessions, by presenting the US alone (CS−/US+).
Results
Evidence for CRs was found only with the short ITI paradigm. The magnitudes of CRs were smaller than TMS-induced MEPs, and the CRs were found only in a percentage of tests. Prepulse inhibition was robustly evident for the long ITI paradigm, but not for the short ITI paradigm.
Conclusions
We have found evidence that classical conditioning principles can be applied to brain stimulation in humans. These findings provide a method for exploring brain and behavioral relationships in humans, as well as suggesting approaches to enhance therapeutic uses of TMS or other forms of brain stimulation.
aDepartments of Neuroscience and Psychiatry, Medical University of South Carolina, Charleston, South Carolina
bDepartment of Psychology, University of South Carolina, Charleston, South Carolina
cShirley L. Buchanan Neuroscience Laboratory, Dorn VA Medical Center, Columbia, South Carolina
dDepartment of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas
eDepartment of Biostatistics, Bioinformatics, and Epidemiology, Medical University of South Carolina, Charleston, South Carolina
fDepartments of Psychiatry, Radiology, and Neurology, Medical University of South Carolina, Charleston, South Carolina
Correspondence: Kevin A. Johnson, Medical University of South Carolina, Brain Stimulation Laboratory, 67 President Street, Room 502N, Charleston, SC 29425.
This work was developed as part of the K.A.J. dissertation research and was presented at the American College of Neuropsychopharmacology.
The views expressed herein are those of the authors and do not necessarily reflect the views of the US Department of Veterans Affairs or the Veterans Administration.
ABSTRACT