159
Static, Low-Frequency, and Pulsed Magnetic Fields
Strafella, Ko, and Monchi (2006) examined placebo effects on patients with PD using
sham rTMS (placebo-rTMS) alone. The authors measured the changes in striatal [11C]
raclopride binding potentials (BP) together with positron emission tomography (PET).
Placebo-rTMS induced significant bilateral reduction in [ 11 C] raclopride BP in dorsal
and ventral striatum as compared with the baseline condition. This reduction in BP is
indicative of an increase in dopamine neurotransmission. The changes in [ 11 C] raclopride binding were more evident in the hemisphere contralateral to the more affected
side, supporting the hypothesis that the more severe the symptoms the greater the drive
for symptom relief and therefore the placebo response. This is the first study addressing
the placebo contribution during rTMS. Although the results seemed to confirm earlier
evidence that expectation induces dopaminergic placebo effects, they also suggested the
importance of placebo-controlled studies in future clinical trials involving brain stimulation techniques.
Kamida et al. (2007) assessed whether paired-pulse TMS–induced MEP can predict
surgical prognosis in patients with intractable epilepsy. The MEP of unilateral hand
muscles were recorded following paired-pulse TMS of the motor cortex. The authors
concluded that paired-pulse TMS–induced MEP may provide predictive value in terms
of surgical outcomes in patients with intractable epilepsy.
Jung et al. (2008) investigated the changes in cortical excitability of the human motor
cortex induced by rTMS (10 Hz, produced MEP of greater than or equal to 50 μV) of
different stimulation durations (5 and 1.5 seconds) over the motor hot spot for left
FDI muscle. The authors concluded that with different stimulation durations, highfrequency subthreshold rTMS can produce different patterns of long-lasting changes in
corticospinal and intracortical excitability in stimulated and unstimulated motor cortex
in healthy subjects. The results have important implications for the selection of stimulation parameters other than the frequency of rTMS.
Because DLPFC is a common target for rTMS experiments and therapeutic protocols,
Fitzgerald et al. (2009) investigated the optimal method for the localization of DLPFC
for use in these studies. Twelve healthy subjects underwent a structural MRI scan, a
TMS procedure to establish the location of the motor cortex, and a neuronavigational
procedure to assess the relative position of the DLPFC. Several EEG points and a position 5 cm anterior to motor cortex were established. The DLPFC site used was identified as being approximately halfway between the EEG points F3 and AF3. This point is
considerably more anterior than the point identified by measuring 5 cm anterior to the
motor cortex. The authors concluded that EEG points provide a useful way to optimally
identify the DLPFC site.
Metaplasticity refers to activity-dependent changes in neural functions that modulate subsequent synaptic plasticity such as long-term potentiation (LTP) and long-term
depression (LTD) (Abraham 2008). Using rTMS (20 Hz, produced MEP of greater than
or equal to 50 μV), Cohen et al. (2010) investigated whether metaplasticity is dependent
on a particular phase of the normal sleep–wake/circadian cycle. The authors suggested
that the timing of sessions relative to the sleep–wake/circadian cycle may be a critical
factor in the cumulative effect of treatment.
Filipović, Rothwell, and Bhatia (2010) demonstrated that low-frequency (≤1 Hz) rTMS
(LF-rTMS) can reduce excitability in the underlying cortex, promote inhibition, or do
Static, Low-Frequency, and Pulsed Magnetic Fields
Strafella, Ko, and Monchi (2006) examined placebo effects on patients with PD using
sham rTMS (placebo-rTMS) alone. The authors measured the changes in striatal [11C]
raclopride binding potentials (BP) together with positron emission tomography (PET).
Placebo-rTMS induced significant bilateral reduction in [ 11 C] raclopride BP in dorsal
and ventral striatum as compared with the baseline condition. This reduction in BP is
indicative of an increase in dopamine neurotransmission. The changes in [ 11 C] raclopride binding were more evident in the hemisphere contralateral to the more affected
side, supporting the hypothesis that the more severe the symptoms the greater the drive
for symptom relief and therefore the placebo response. This is the first study addressing
the placebo contribution during rTMS. Although the results seemed to confirm earlier
evidence that expectation induces dopaminergic placebo effects, they also suggested the
importance of placebo-controlled studies in future clinical trials involving brain stimulation techniques.
Kamida et al. (2007) assessed whether paired-pulse TMS–induced MEP can predict
surgical prognosis in patients with intractable epilepsy. The MEP of unilateral hand
muscles were recorded following paired-pulse TMS of the motor cortex. The authors
concluded that paired-pulse TMS–induced MEP may provide predictive value in terms
of surgical outcomes in patients with intractable epilepsy.
Jung et al. (2008) investigated the changes in cortical excitability of the human motor
cortex induced by rTMS (10 Hz, produced MEP of greater than or equal to 50 μV) of
different stimulation durations (5 and 1.5 seconds) over the motor hot spot for left
FDI muscle. The authors concluded that with different stimulation durations, highfrequency subthreshold rTMS can produce different patterns of long-lasting changes in
corticospinal and intracortical excitability in stimulated and unstimulated motor cortex
in healthy subjects. The results have important implications for the selection of stimulation parameters other than the frequency of rTMS.
Because DLPFC is a common target for rTMS experiments and therapeutic protocols,
Fitzgerald et al. (2009) investigated the optimal method for the localization of DLPFC
for use in these studies. Twelve healthy subjects underwent a structural MRI scan, a
TMS procedure to establish the location of the motor cortex, and a neuronavigational
procedure to assess the relative position of the DLPFC. Several EEG points and a position 5 cm anterior to motor cortex were established. The DLPFC site used was identified as being approximately halfway between the EEG points F3 and AF3. This point is
considerably more anterior than the point identified by measuring 5 cm anterior to the
motor cortex. The authors concluded that EEG points provide a useful way to optimally
identify the DLPFC site.
Metaplasticity refers to activity-dependent changes in neural functions that modulate subsequent synaptic plasticity such as long-term potentiation (LTP) and long-term
depression (LTD) (Abraham 2008). Using rTMS (20 Hz, produced MEP of greater than
or equal to 50 μV), Cohen et al. (2010) investigated whether metaplasticity is dependent
on a particular phase of the normal sleep–wake/circadian cycle. The authors suggested
that the timing of sessions relative to the sleep–wake/circadian cycle may be a critical
factor in the cumulative effect of treatment.
Filipović, Rothwell, and Bhatia (2010) demonstrated that low-frequency (≤1 Hz) rTMS
(LF-rTMS) can reduce excitability in the underlying cortex, promote inhibition, or do