Figure 1.
The paired-pulse transcranial magnetic stimulation protocol.
(A) Motor evoked potentials (¥) were recorded from the abductor pollicis brevis muscle following magnetic stimulation of the motor cortex. The stimulus intensity required to achieve a target response of 0.2 mV, defined as the resting motor threshold (RMT), was determined following a single magnetic stimulus. (B) Pairs of pulses were then delivered; a conditioning impulse with an intensity set at 70% of RMT (*) followed by a test impulse which varied in intensity in order to maintain the target response of 0.2 mV. As the protocol proceeded, the interval between the two stimuli – defined as the interstimulus interval (∂) – was varied from 1–20 ms. SICI was defined as the increase in test impulse intensity (i.e. test - RMT) required to achieve the target response at interstimulus intervals of 1–7 ms, represented as a percentage of RMT. Please note, this figure (A) is simply intended to illustrate how the RMT is determined and the response reproduced here does not necessarily represent an accurate measurement of RMT. Furthermore, the intensities of the stimuli used in A and B differ; therefore the larger amplitude motor response in B does not necessarily reflect intracortical facilitation following the conditioning impulse.
Table 1.
Characteristics of Individual CBS patients.
Table 2.
Clinical Characteristics of CBS patients.
Figure 2.
Cortical hyper-excitability in corticobasal syndrome.
Patients with CBS had evidence of cortical hyper-excitability, with reduced SICI (A), significantly (P<0.05) reduced average SICI (B), and significantly (P<0.05) increased motor evoked potential – expressed as a ratio of compound motor action potential amplitude (C). Abbreviations: CBS = corticobasal syndrome, SICI = short-interval intracortical inhibition, MEP = motor evoked potential, CMAP = compound motor action potential.
Table 3.
Cortical excitability in CBS patients.
Table 4.
Clinical features of CBS patients when grouped according to resting motor threshold.
Figure 3.
Voxel-based morphometry analysis demonstrating brain regions that positively correlate with neurophysiological parameters in CBS patients.
(A) Reduced RMT correlated with atrophy of the primary motor cortex (red circles), thalamus (blue circle) and the anterior temporal lobe (magenta circle). (B) Reduced SICI correlated with atrophy of the primary motor cortex (red circle), thalamus (blue circles), medial frontal cortex (yellow circles) and precuneus (green circles). Clusters are overlaid on the Montreal Neurological Institute standard brain (t>2.41). Colored voxels show regions that were significant in the analyses for P<0.001 uncorrected and a cluster threshold of 20 contiguous voxels. Circled areas indicate: red = primary motor cortex; blue = thalamus; magenta = anterior temporal lobe; yellow = medial frontal cortex; green = precuneus.
Figure 4.
Voxel-based morphometry analysis with the apraxia score as a covariate in CBS patients.
The degree of apraxia (as reflected in an increased apraxia score) correlated with atrophy of the medial frontal cortex (red circles) and the precuneus/posterior cingulate (blue circles). Clusters are overlaid on the Montreal Neurological Institute standard brain (t>2.41). Colored voxels show regions that were significant in the analyses for P<0.001 uncorrected and a cluster threshold of 20 contiguous voxels. Circled areas indicate: red = medial frontal cortex; blue = precuneus/posterior cingulate.