160
Electromagnetic Fields in Biological Systems
both. In particular, using LF-rTMS the authors found the impaired inhibitory mechanisms in motor cortex of patients with PD. Previously, Filipović et al. (2009) examined
the effects of LF-rTMS (1 Hz, 1800 pulses) on dyskinesia in PD. The stimulator intensity was set individually to just below the aMT. The LF-rTMS was applied twice over
the motor cortex for four consecutive days; once real stimuli were used and once sham
stimulation was used. Evaluations were done at the baseline and one day after the end
of each treatment series. Filipović, Rothwell, and Bhatia (2010) further evaluated the
delayed (24-hour) effects of LF-rTMS treatment on physiological measures of excitability
of the motor cortex in the same patients. The authors found that LF-rTMS delivered over
several consecutive days changes the excitability of the motor cortex by increasing the
excitability of inhibitory circuits. The effects persist for at least a day after rTMS.
Shirota et al. (2010) evaluated cerebellar function using TMS to determine whether
subclinical cerebellar involvement is present in progressive supranuclear palsy (PSP)
patients. The authors studied 11 patients with PSP, 11 patients with PD, and 10 agematched controls. Motor-evoked potentials were recorded from the hand muscle.
Cerebellar function was evaluated using suppressive effects of TMS over the cerebellum
on MEP elicited by TMS over the contralateral motor cortex, which is called cerebellar
inhibition (CBI). Interstimulus intervals of 4–8 milliseconds were used, and the time
course of CBI was analyzed. The CBI was found to be reduced in PSP patients. By contrast, the CBI was normal in PD patients in their on state (phases with good response
to medication and few symptoms). Although the CBI in their off state (phases with no
response to medication and more severe symptoms) should be examined in future studies, the results suggested that Purkinje cells or the dentatothalamocortical pathway
assessed by CBI is involved in PSP. These results are compatible with the pathological
findings showing severe dentate nucleus degeneration in PSP patients.
Hiscock et al. (2008) reviewed evidence regarding the effect of rTMS on corticospinal
pathway excitability and motor function in healthy adults and in people in the aftermath
of stroke. After stroke there was a trend for MEP recovery (i.e., presence of MEP) after
10 daily sessions of 3 Hz rTMS (one study). Motor function in healthy adults might be
adversely affected by 1 Hz rTMS (two studies), whereas combined frequency rTMS was
found to have no effect on motor function (one study). The authors concluded that there
is as yet insufficient published evidence to guide the dosage of rTMS to the lesioned
hemisphere after stroke to improve recovery of a paretic limb. Moreover, apparently
there is variability in response to rTMS in healthy adults.
Contralesional dorsal premotor cortex (cPMd) may support residual motor function
following stroke. Using TMS-fMRI, Bestmann et al. (2010) performed two complementary experiments to explore how cPMd might perform this role in a group of chronic
stroke patients. First, they used paired-coil TMS (11 Hz) to establish the physiological
influence of cPMd on ipsilesional primary motor cortex (iM1) at rest. They found that
this influence became less inhibitory/more facilitatory in patients with greater clinical
impairment. Second, they applied TMS over cPMd during fMRI (1.5 T) in these patients
to examine the causal influence of cPMd TMS on the whole network of surviving cortical motor areas in both hemispheres and to check whether these influences could change
during movement of the affected hand after stroke. The authors confirmed that hand
grip–related activation in cPMd was greater in more impaired patients. Furthermore,
Electromagnetic Fields in Biological Systems
both. In particular, using LF-rTMS the authors found the impaired inhibitory mechanisms in motor cortex of patients with PD. Previously, Filipović et al. (2009) examined
the effects of LF-rTMS (1 Hz, 1800 pulses) on dyskinesia in PD. The stimulator intensity was set individually to just below the aMT. The LF-rTMS was applied twice over
the motor cortex for four consecutive days; once real stimuli were used and once sham
stimulation was used. Evaluations were done at the baseline and one day after the end
of each treatment series. Filipović, Rothwell, and Bhatia (2010) further evaluated the
delayed (24-hour) effects of LF-rTMS treatment on physiological measures of excitability
of the motor cortex in the same patients. The authors found that LF-rTMS delivered over
several consecutive days changes the excitability of the motor cortex by increasing the
excitability of inhibitory circuits. The effects persist for at least a day after rTMS.
Shirota et al. (2010) evaluated cerebellar function using TMS to determine whether
subclinical cerebellar involvement is present in progressive supranuclear palsy (PSP)
patients. The authors studied 11 patients with PSP, 11 patients with PD, and 10 agematched controls. Motor-evoked potentials were recorded from the hand muscle.
Cerebellar function was evaluated using suppressive effects of TMS over the cerebellum
on MEP elicited by TMS over the contralateral motor cortex, which is called cerebellar
inhibition (CBI). Interstimulus intervals of 4–8 milliseconds were used, and the time
course of CBI was analyzed. The CBI was found to be reduced in PSP patients. By contrast, the CBI was normal in PD patients in their on state (phases with good response
to medication and few symptoms). Although the CBI in their off state (phases with no
response to medication and more severe symptoms) should be examined in future studies, the results suggested that Purkinje cells or the dentatothalamocortical pathway
assessed by CBI is involved in PSP. These results are compatible with the pathological
findings showing severe dentate nucleus degeneration in PSP patients.
Hiscock et al. (2008) reviewed evidence regarding the effect of rTMS on corticospinal
pathway excitability and motor function in healthy adults and in people in the aftermath
of stroke. After stroke there was a trend for MEP recovery (i.e., presence of MEP) after
10 daily sessions of 3 Hz rTMS (one study). Motor function in healthy adults might be
adversely affected by 1 Hz rTMS (two studies), whereas combined frequency rTMS was
found to have no effect on motor function (one study). The authors concluded that there
is as yet insufficient published evidence to guide the dosage of rTMS to the lesioned
hemisphere after stroke to improve recovery of a paretic limb. Moreover, apparently
there is variability in response to rTMS in healthy adults.
Contralesional dorsal premotor cortex (cPMd) may support residual motor function
following stroke. Using TMS-fMRI, Bestmann et al. (2010) performed two complementary experiments to explore how cPMd might perform this role in a group of chronic
stroke patients. First, they used paired-coil TMS (11 Hz) to establish the physiological
influence of cPMd on ipsilesional primary motor cortex (iM1) at rest. They found that
this influence became less inhibitory/more facilitatory in patients with greater clinical
impairment. Second, they applied TMS over cPMd during fMRI (1.5 T) in these patients
to examine the causal influence of cPMd TMS on the whole network of surviving cortical motor areas in both hemispheres and to check whether these influences could change
during movement of the affected hand after stroke. The authors confirmed that hand
grip–related activation in cPMd was greater in more impaired patients. Furthermore,