Prefrontal TMS produces smaller EEG responses than motor-cortex TMS: implications for rTMS treatment in depression

RationaleThe stimulus intensity of prefrontal repetitive transcranial magnetic stimulation (rTMS) during depression treatment is usually determined by adjusting it with respect to the motor threshold (MT). There is some evidence that reactivity of the prefrontal cortex to transcranial magnetic stimulation (TMS) is lower than that of the motor cortex at MT stimulation. However, it is unknown whether this is true when other stimulus intensities are used. We investigated whether the magnitude and shape of the overall TMS-evoked electroencephalographic (EEG) responses differ between prefrontal and motor cortices.MethodsMagnetic pulses to the left motor and prefrontal cortices (the middle frontal gyrus identified from magnetic resonance images) were delivered at four intensities (60, 80, 100, and 120% of MT of the right abductor digiti minimi muscle) for six subjects. Simultaneously, EEG was recorded with 60 scalp electrodes.ResultsGlobal mean-field amplitudes (GMFAs) reflecting overall cortical activity were significantly smaller after prefrontal- than after motor-cortex TMS. A significant positive correlation (rs=0.84, p<0.01) was found between GMFAs of motor- and prefrontal-cortex TMS across the experiments. However, when correlation between the responses of motor and prefrontal cortices was examined, significant positive correlations were found at 80 and 100% intensities only.ConclusionsThis study provides further evidence that the prefrontal and motor cortices have different reactivity to TMS, but the MT may be used for determining the stimulus intensity of prefrontal rTMS treatment in depression, at least at motor threshold intensities or near to it.

[1]  Frank Padberg,et al.  Plasma Concentrations of Neuroactive Steroids before and after Repetitive Transcranial Magnetic Stimulation (rTMS) in Major Depression , 2002, Neuropsychopharmacology.

[2]  Risto J. Ilmoniemi,et al.  Distinct differences in cortical reactivity of motor and prefrontal cortices to magnetic stimulation , 2004, Clinical Neurophysiology.

[3]  F. Holsboer,et al.  Transcranial magnetic stimulation as a therapeutic tool in psychiatry: what do we know about the neurobiological mechanisms? , 2001, European Psychiatry.

[4]  R. J. Ilmoniemi,et al.  Prefrontal transcranial magnetic stimulation produces intensity-dependent EEG responses in humans , 2005, NeuroImage.

[5]  M. Hallett,et al.  Optimal Focal Transcranial Magnetic Activation of the Human Motor Cortex: Effects of Coil Orientation, Shape of the Induced Current Pulse, and Stimulus Intensity , 1992, Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society.

[6]  R. J. Ilmoniemi,et al.  Instrumentation for the measurement of electric brain responses to transcranial magnetic stimulation , 1999, Medical & Biological Engineering & Computing.

[7]  H. Möller,et al.  Repetitive Transcranial Magnetic Stimulation (rTMS) in Major Depression: Relation between Efficacy and Stimulation Intensity , 2002, Neuropsychopharmacology.

[8]  Seppo Kähkönen,et al.  The effect of stimulus intensity on brain responses evoked by transcranial magnetic stimulation , 2004, Human brain mapping.

[9]  S Kähkönen,et al.  The functional connectivity of the prefrontal cortex studied by combined TMS with EEG , 2001 .

[10]  Frank Padberg,et al.  Transcranial magnetic stimulation in therapy studies: examination of the reliability of “standard” coil positioning by neuronavigation , 2001, Biological Psychiatry.

[11]  N. Petersen,et al.  On the comparability of H-reflexes and MEPs. , 1999, Electroencephalography and clinical neurophysiology. Supplement.

[12]  B. Meyer,et al.  Evaluation of cortical excitability by motor and phosphene thresholds in transcranial magnetic stimulation , 2003, Journal of the Neurological Sciences.

[13]  W. H. Howell,et al.  A TEXTBOOK OF PHYSIOLOGY , 1934 .

[14]  P. Rossini,et al.  Non-invasive electrical and magnetic stimulation of the brain, spinal cord and roots: basic principles and procedures for routine clinical application. Report of an IFCN committee. , 1994, Electroencephalography and clinical neurophysiology.

[15]  S. Gandevia,et al.  Double-blind controlled investigation of transcranial magnetic stimulation for the treatment of resistant major depression. , 1999, The American journal of psychiatry.

[16]  J. Nielsen,et al.  Recruitment of extensor-carpi-radialis motor units by transcranial magnetic stimulation and radial-nerve stimulation in human subjects , 1999, Experimental Brain Research.

[17]  J. Rothwell,et al.  Motor and phosphene thresholds: a transcranial magnetic stimulation correlation study , 2001, Neuropsychologia.

[18]  Seppo Kähkönen,et al.  Alcohol Reduces Prefrontal Cortical Excitability in Humans: A Combined TMS and EEG Study , 2003, Neuropsychopharmacology.

[19]  Á. Pascual-Leone,et al.  Rapid-rate transcranial magnetic stimulation of left dorsolateral prefrontal cortex in drug-resistant depression , 1996, The Lancet.

[20]  Klaus P. Ebmeier,et al.  Reduced cortical excitability in depression , 1999, British Journal of Psychiatry.

[21]  J. Lorberbaum,et al.  The transcranial magnetic stimulation motor threshold depends on the distance from coil to underlying cortex: a replication in healthy adults comparing two methods of assessing the distance to cortex , 2001, Biological Psychiatry.

[22]  E. Fetz Fetz Motor Functions of Cerebral Cortex , 2007 .

[23]  Á. Pascual-Leone,et al.  Interhemispheric asymmetry of motor cortical excitability in major depression as measured by transcranial magnetic stimulation , 2000, British Journal of Psychiatry.

[24]  Henrik Foltys,et al.  Visual and motor cortex excitability: a transcranial magnetic stimulation study , 2002, Clinical Neurophysiology.

[25]  Sauli Savolainen,et al.  Ipsi- and contralateral EEG reactions to transcranial magnetic stimulation , 2002, Clinical Neurophysiology.

[26]  A. Gershon,et al.  Transcranial magnetic stimulation in the treatment of depression. , 2003, The American journal of psychiatry.

[27]  M I Mendel,et al.  Audiometric comparison of the middle and late components of the adult auditory evoked potentials awake and asleep. , 1975, Electroencephalography and clinical neurophysiology.

[28]  J. Mann,et al.  The functional neuroanatomy of mood disorders. , 1997, Journal of psychiatric research.

[29]  J. Lorberbaum,et al.  How coil-cortex distance relates to age, motor threshold, and antidepressant response to repetitive transcranial magnetic stimulation. , 2000, The Journal of neuropsychiatry and clinical neurosciences.