Relationship between thalamic and scalp alpha rhythms in man -with cross-spectral analysis-

Thalamic and acalp EEGs were recorded simultaneously during stereotaxic surgery. Thalamic EEGs were recorded from the ventro-lateral (VL) nucleus of the thalamus in 19 patients with parkinsonism, and from the centre median (CM) nucleus in 3 with intractable pain. Scalp EEGs following thalamotomy were also recorded. These EEGs were analyzed quantitatively by means of cross-spectral analysis. The relationships between thalamic and scalp alpha rhythms and postoperative changes of scalp alpha rhythms were studied to investigate the hypothesis that the cortical alpha rhythms are paced by thalamic generators. The results were as follows: 1) The alpha rhythms in the thalamic VL and CM nuclei had the same frequency components as those in the scalp, and were more regular and predominant than those in the scalp. 2) Significant coherences were found between alpha rhythms in the thalamic VL and CM nuclei and those in the bilateral frontal, central and parietal scalp regions. The stronger coherences were found between VL thalamic alpha rhythms and frontal and central ones, and between CM thalamic alpha rhythms and central and parietal ones. 3) Among these alpha rhythms, there were found constant phase relationships that the alpha rhythms from the VL or CM thalamic nucleus were followed, in the order of time lag, by the scalp ones in the frontal, central and then parietal regions without interhemispheric phase lag. Interhemispheric time lag was not found. 4) The alpha-coherences between the contralateral central scalp region and the VL or CM nucleus were apt to be stronger than those between the two hemispheres.5) The alpha-coherences between the central scalp region and the CM nucleus were stronger than those between the central scalp region and the dorsomedial nucleus. 6) Intrathalamic and intrahemispheric alpha-coherences were stronger than those between thalamus and scalp. Intrathalamic alpha-coherences were the strongest and had a broad bandwidth. 7) Following VL or CM thalamotomy, alpha rhythms in the frontal, central and parietal regions slowed and became irregular in frequency, but the phase relationships in these alpha rhythms remained the same as preoperative ones which spread in anteroposterior direction. However, the coherences between the fronto-centro-parietal alpha rhythms and the occipital alpha rhythms became lessened and the phase lag between parietal and occipital alpha rhythms was prolonged. On the basis of these findings, it seems to indicate that the thalamus, with close intrathalamic and internuclear relationships, has an ability to generate more stable and regular alpha rhythms than the cortex, and that the individual thalamic nucleus has the ability to generate intrinsic alpha rhythms and to regulate the alpha rhythms arising in the cortical area which receives projections from the thalamic nucleus. It also suggests that the alpha rhythms in the fronto-centro-parietal cortex, with close relationships with VL and CM nucleus, are different to some degree in synchronization from the occipital alpha rhythms