**2.6 Cortical plasticity**

Repetitive TMS has also been applied to investigate motor cortex plasticity in patients with Becker muscular dystrophy [9]. The rTMS-induced facilitation of MEPs was significantly reduced in mentally retarded or borderline mentally retarded classified BMD patients when compared with BMD patients with normal intelligence and age-matched healthy controls (see **Figure 1a**). The increase in the duration of the cortical silent periods was similar in both patient groups and controls (see **Figure 1b**). These findings suggest an altered cortical short-term synaptic plasticity in glutamate-dependent excitatory circuits within the motor cortex in BMD patients with intellectual disabilities.

**55**

**Figure 1.**

*between patients and controls.*

*Electrophysiological Assessment of CNS Abnormalities in Muscular Dystrophy*

*(a and b) Changes in the size of motor evoked potentials (a) and in the duration of cortical silent period (b) in the FDI muscle during repetitive transcranial magnetic stimulation trains of 10 pulses delivered at 5 Hz in the 6 patients with Becker muscular dystrophy and mental retardation or borderline (BMD-Cog−), the 7 patients with BMD and normal intelligence (BMD-Cog+), and the 10 age-matched healthy subjects (controls). Data are expressed as mean ± SE. Asterisks indicate significant differences (p < 0.05, Bonferroni adjusted)* 

*DOI: http://dx.doi.org/10.5772/intechopen.86256*

*Electrophysiological Assessment of CNS Abnormalities in Muscular Dystrophy DOI: http://dx.doi.org/10.5772/intechopen.86256*

#### **Figure 1.**

*Muscular Dystrophies*

feature of myopathies.

**2.5 TMS and fatigue**

of these patients.

sate for muscle weakness.

**2.6 Cortical plasticity**

in patients in contrast to the healthy controls.

BMD patients with intellectual disabilities.

irrespective of the type of myopathy, a reduced intracortical inhibition was found. Obviously, this neurobiological mechanism of increased motor cortical excitability for compensation of muscle weakness is independent of a particular muscle pathology in myopathies. However, with regard to the available electrophysiological data, there is no sufficient evidence to conclude that cortical disinhibition is a common

In 2004 Di Lazzaro et al. reported significantly reduced SICI in early-onset FSHD patients compared with patients suffering from other muscle diseases (LGMD and polymyositis) and healthy controls. Between polymyositis patients and

During fatiguing muscle exercise, a paired-pulse TMS paradigm can be applied to investigate the central inhibitory and excitatory mechanisms that occur at the motor cortical level. Paired-pulse TMS was already done in patients with multiple sclerosis and in healthy subjects [15, 16]. In a study of Schwenkreis et al., SICI has been applied prior to a fatiguing motor task, immediately post-exercise, and 40 minutes post-exercise in MD patients and patients suffering from fibromyalgia syndrome (FMS) [17]. In the MD and FMS patients, SICI was already reduced pre-exercise. Healthy subjects did not show any pre-exercise SICI decrease but a significant SICI decrease post-exercise. Thus, reduced SICI may be a central compensatory mechanism for peripheral or central fatigue. MD patients may use this neurobiological mechanism of reduced SICI already under baseline conditions, probably due to permanent muscle weakness. Probably due to a ceiling effect, the MD and FMS patients may not be able to further decrease cortical inhibition during the fatiguing exercise. This may be an additional central mechanism to the fatigue in MD and FMS patients. A fatigue syndrome belongs to the typical clinical feature

An altered peripheral nerve excitability and reduced SICI at baseline in patients with MD type 1 (DM1) with impaired myoelectric properties (mean power frequency, muscle fiber conduction velocity) have been demonstrated in a study of Boerio et al. [18]. The remaining excitability parameters did not vary post-exercise

In patients with colchicine myopathy with reported fatigue but no significant muscle weakness, Lin et al. investigated central compensatory mechanisms [19]. The patient and control group did not differ in the results. Obviously, there is no change in motor cortical excitability in acquired myopathy due to colchicine, while central reorganization may occur in patients with hereditary myopathy to compen-

Repetitive TMS has also been applied to investigate motor cortex plasticity in patients with Becker muscular dystrophy [9]. The rTMS-induced facilitation of MEPs was significantly reduced in mentally retarded or borderline mentally retarded classified BMD patients when compared with BMD patients with normal intelligence and age-matched healthy controls (see **Figure 1a**). The increase in the duration of the cortical silent periods was similar in both patient groups and controls (see **Figure 1b**). These findings suggest an altered cortical short-term synaptic plasticity in glutamate-dependent excitatory circuits within the motor cortex in

controls, there was no significant difference in SICI [13].

**54**

*(a and b) Changes in the size of motor evoked potentials (a) and in the duration of cortical silent period (b) in the FDI muscle during repetitive transcranial magnetic stimulation trains of 10 pulses delivered at 5 Hz in the 6 patients with Becker muscular dystrophy and mental retardation or borderline (BMD-Cog−), the 7 patients with BMD and normal intelligence (BMD-Cog+), and the 10 age-matched healthy subjects (controls). Data are expressed as mean ± SE. Asterisks indicate significant differences (p < 0.05, Bonferroni adjusted) between patients and controls.*
