The purpose of this study was to clarify the relationships between the distributions and cortical sources of two types of spindles in the magnetoencephalogram (MEG) and how cortical activating areas contribute to the distribution of spindles. Spontaneous activities during sleep stage 2 were recorded from 7 normal subjects by simultaneous EEG and MEG recordings. Two types of spindles with frequency-specific topographic differences (fast spindles and slow spindles) were defined by EEG, and, subsequently, the sources of spindles were estimated as equivalent current dipoles using MEG. Activation centered in four areas, the precentral and postcentral areas in posterior frontal cortex and parietal cortex of each hemisphere. However, these areas were not always activated simultaneously. Fast spindles were associated with more frequent activation of postcentral areas with stronger activation strengths, whereas slow spindles were associated with more frequent activation of precentral areas with stronger activation strengths. When spindles were distributed symmetrically in amplitude between the hemispheres on both EEG and MEG, the four areas were activated equally and simultaneously. When spindles exhibited asymmetric distributions with amplitude differences above 30% between hemispheres, the cortical areas were activated with variable temporal relationships. Two types of spindle oscillations observed in the MEG had a common neural basis at the cortical level, with variability in patterns of activation and activation strengths resulting in the differences in distribution observed on the EEG and MEG. The differences in cortical activation patterns and activation strengths between the two types of spindles suggest that two distinct forms of spindle bursts propagate to cortex through different underlying neuronal circuits. Defining the cortical activating areas for spindles by MEG is valuable to consider the underlying neural basis.

No abstract

Few methods can predict the prognosis and outcome of traumatic brain injury. Electroencephalographic (EEG) examinations have prognostic significance in the acute stage of posttraumatic coma, and some EEG variables have been correlated with outcome. Furthermore, spindle activity and reactivity in the acute stage have been associated with good recovery. Assessments of consciousness based on EEG and magnetoencephalographic (MEG) recordings provide valuable information for evaluating residual function, forming differential diagnoses and estimating prognosis. This study objectively investigated how fast spindles could relate to the recovery of consciousness and cognitive function during the post-acute to chronic stages of diffuse axonal injuries (DAIs). Sleep stage 2 was examined in 7 healthy participants and 8 patients with DAIs. Simultaneous EEG and MEG recordings were performed in the post-acute (mean 80 days) and chronic (mean 151 days) stages of recovery. Magnetoencephalography enabled equivalent current dipole estimates of fast spindle sources. Clinical recovery was evaluated by consciousness, neuropsychological examination, and outcome. Six severe and two moderate injuries were studied in patients with favorable 1-year outcomes. In the sub-acute stage, significant decreases were detected in the frequency, amplitude, and cortical activation source strengths of spindle activities, but these recovered during the chronic stage. In the chronic stage, the Wechsler adult intelligence factor scale and subset patterning revealed significant improvement in cognitive function. These results suggested that spindles may reflect recovery of consciousness and cognitive function following a DAI.

The midline theta rhythm consists of runs of theta waves occurring in the midline, especially in the central and parietal vertex regions. Few reports regarding this uncommon EEG finding have been published. It has been given various names, e.g. theta discharges in the middle-line, theta spindles, etc. Out of the 4,236 patients who were administered EEG examinations during an investigation period of 9 months, the midline theta rhythm, with a frequency in the range of 4-7 Hz, voltage over 50 microV, duration over 3 seconds, and most prominent in the central and parietal vertex areas, was recorded in 35 (0.83%). The age distribution of these patients peaked in two groups, adults aged 21-40 years and elderly patients aged 61-77 years. The waveform of the theta rhythm observed in adults 40 years old and under was often sinusoidal and regular. In this group, the most common clinical disorder was epilepsy. Often, the appearance of the theta rhythm observed in elderly patients was triangular and irregular, and sometimes sharp. In this group, the common clinical symptoms were headaches and dizziness, characterized by diagnoses of organic brain diseases such as cerebrovascular disorders. This study re-examines the clinical significance of the midline theta rhythm, taking into consideration studies that have been published in the past.

This study aimed to determine the relationships between the amplitude and cortical-activating areas in each hemisphere for 14-Hz centro-parietal spindles to clarify the involvement of the cortex in the asymmetry of spindles after hemispheric stroke with putaminal or thalamic hemorrhage using simultaneous recording of the electroencephalogram and magnetoencephalogram. Spontaneous cortical activities during sleep stage 2 (spindles) were simultaneously recorded from 10 patients with putaminal or thalamic hemorrhage with a 60-channel electroencephalogram and a 306-channel whole-head magnetoencephalogram. Based on the frequencies and cortical distributions recorded with electroencephalogram, the 14-Hz centro-parietal and 12-Hz frontal spindles were differentiated. The cortical sources of the 14-Hz centro-parietal spindles were identified with magnetoencephalogram as equivalent current dipoles. Activation centered in four areas, the pre- and postcentral areas in posterior frontal cortex and parietal cortex of each hemisphere. However, these areas were not always activated simultaneously. Reduction of amplitude in the affected hemisphere after hemispheric stroke indicated reduction of areas of activation or activation strengths in the ipsilateral hemisphere. For some spindles, when reduction of amplitude of above 50% occurred in the affected hemisphere compared with the nonaffected hemisphere, no activation occurred in the ipsilateral hemisphere. Reduction of amplitude was related to the reduction of areas of cortical activation and activation strengths. Reduction of amplitude also occurred over the nonaffected hemisphere, and reduction of cortical activating area and activation occurred in the nonaffected hemisphere, suggesting that the cerebral hemispheres are involved in the eneration of spontaneous sleep spindles. The stronger ipsilateral effects of cerebral lesions on spindle oscillations indicated reduction of amplitude of sleep spindles in the ipsilateral hemisphere, as well as reduction of cortical activation of spindle oscillations and underlying corticothalamic projections. Simultaneous electroencephalogram and magnetoencephalogram recordings can yield valuable findings concerning the functional asymmetry between hemispheres after hemispheric stroke from the relationships between the amplitude and patterns of cortical activation associated with spindles.