Rhythm is determined solely by the relationship between the time intervals of a series of events. Psychological studies have proposed two types of rhythm representation depending on the interval ratio of the rhythm: metrical and nonmetrical representation for rhythms formed with small integer ratios and noninteger ratios, respectively. We used functional magnetic resonance imaging to test whether there are two neural representations of rhythm depending on the interval ratio. The subjects performed a short-term memory task for a seven-tone rhythm sequence, which was formed with 1:2:4, 1:2:3, or 1:2.5:3.5 ratios. The brain activities during the memory delay period were measured and compared with those during the retention of a control tone sequence, which had constant intertone intervals. The results showed two patterns of brain activations; the left premotor and parietal areas and right cerebellar anterior lobe were active for 1:2:4 and 1:2:3 rhythms, whereas the right prefrontal, premotor, and parietal areas together with the bilateral cerebellar posterior lobe were active for 1:2.5:3.5 rhythm. Analysis on individual subjects revealed that these activation patterns depended on the ratio of the rhythms that were produced by the subjects rather than the ratio of the presented rhythms, suggesting that the observed activations reflected the internal representation of rhythm. These results suggested that there are two neural representations for rhythm depending on the interval ratio, which correspond to metrical and nonmetrical representations.

Paired-pulse magnetic stimulation techniques have been used to study the intracortical circuitry of the motor cortex in humans. There are several paired stimulation methods. Two of them have been used for studying inhibitory and facilitatory connections in the motor cortex at short interstimulus intervals (ISIs). When the first stimulus (S1) is subthreshold and the second (S2) suprathreshold, electromyographic (EMG) responses to both stimuli are smaller than the responses to S2 alone at short ISIs (1-5 ms; intracortical inhibition) and larger at longer ISIs (Kujirai et al. 1993). In contrast, when S1 is suprathreshold and S2 subthreshold, EMG responses to both stimuli can be larger than the control responses at ISIs of 1.3, 2.6 and 4.0 ms (Tokimura et al. 1996; Nakamura et al. 1997b; Ziemann et al. 1998;Rothwell, 1999). These two effects were not observed when S2 was a low intensity anodal electrical stimulus, which tends to evoke D-waves (direct waves: descending volleys produced by direct activation of pyramidal tract neurones), but were very clear when S2 was a magnetic stimulus that elicited I-waves (indirect waves: descending volleys produced by indirect activation of pyramidal tract neurones via presynaptic neurones). Based on these results, both effects were considered to be produced at the motor cortex. The latter effect has been termed 'intracortical I-wave facilitation ' (Ziemann et al. 1998).Several studies have shown that later I-waves are more affected by intracortical inhibition than early I-waves (Nakamura et al. 1997a; Hanajima et al. 1998; Di Lazzaro et al. 1998). I3-waves appear to be particularly susceptible to intracortical inhibition, whereas I1-waves are little affected (Hanajima et al. 1998). However, it remains to be determined whether there are differences in intracortical I-wave facilitation among different I-waves. In this paper, in order to clarify details of this effect, we studied intracortical I-wave facilitation of I1-and I3-waves using both single motor unit and surface EMG recordings. METHODS SubjectsTen healthy volunteers (8 men and 2 women; 28-46 years old; height, 143-180 cm; weight, 45-95 kg) were studied. Written informed consent was obtained from all the subjects. Surface EMG recordings were done in all subjects. Single motor unit studies were performed in nine subjects, one subject (a In order to elucidate the mechanisms underlying intracortical I-wave facilitation elicited by pairedpulse magnetic stimulation, we compared intracortical facilitation of I1-waves with that of I3-waves using single motor unit and surface electromyographic (EMG) recordings from the first dorsal interosseous muscle (FDI). We used a suprathreshold first stimulus (S1) and a subthreshold second stimulus (S2). In most experiments, both stimuli induced currents in the same direction. In others, S1 induced posteriorly directed currents and S2 induced anteriorly directed currents. When both stimuli induced anteriorly directed currents (I1-wave effects), an interstimulus interval (ISI) of 1.5 ms res...

CAM includes clinicohistopathologically heterogeneous disease entities. Among CAM entities, anti-TIF1-γ-Ab(+) CAM has characteristically shown a close temporal association with cancer detection and the histopathologic findings of dC5b-9 and VFs, and CAM with NAM is a subset of anti-TIF1-γ-Ab(-) CAM.

Primary lateral sclerosis is a sporadic disorder characterized by slowly progressive corticospinal dysfunction. Primary lateral sclerosis differs from amyotrophic lateral sclerosis by its lack of lower motor neuron signs and long survival. Few pathological studies have been carried out on patients with primary lateral sclerosis, and the relationship between primary lateral sclerosis and amyotrophic lateral sclerosis remains uncertain. To detect in vivo structural differences between the two disorders, diffusion tensor imaging of white matter tracts was carried out in 19 patients with primary lateral sclerosis, 18 patients with amyotrophic lateral sclerosis and 19 age-matched controls. Fibre tracking was used to reconstruct the intracranial portion of the corticospinal tract and three regions of the corpus callosum: the genu, splenium and callosal fibres connecting the motor cortices. Both patient groups had reduced fractional anisotropy, a measure associated with axonal organization, and increased mean diffusivity of the reconstructed corticospinal and callosal motor fibres compared with controls, without changes in the genu or splenium. Voxelwise comparison of the whole brain white matter using tract-based spatial statistics confirmed the differences between patients and controls in the diffusion properties of the corticospinal tracts and motor fibres of the callosum. This analysis further revealed differences in the regional distribution of white matter alterations between the patient groups. In patients with amyotrophic lateral sclerosis, the greatest reduction in fractional anisotropy occurred in the distal portions of the intracranial corticospinal tract, consistent with a distal axonal degeneration. In patients with primary lateral sclerosis, the greatest loss of fractional anisotropy and mean diffusivity occurred in the subcortical white matter underlying the motor cortex, with reduced volume, suggesting tissue loss. Clinical measures of upper motor neuron dysfunction correlated with reductions in fractional anisotropy in the corticospinal tract in patients with amyotrophic lateral sclerosis and increased mean diffusivity and volume loss of the corticospinal tract in patients with primary lateral sclerosis. Changes in the diffusion properties of the motor fibres of the corpus callosum were strongly correlated with changes in corticospinal fibres in patients, but not in controls. These findings indicate that degeneration is not selective for corticospinal neurons, but affects callosal neurons within the motor cortex in motor neuron disorders.