Thalamocortical dysrhythmia: A neurological and neuropsychiatric syndrome characterized by magnetoencephalography

Spontaneous magnetoencephalographic activity was recorded in awake, healthy human controls and in patients suffering from neurogenic pain, tinnitus, P arkinson's disease, or depression. Compared with controls, patients showed increased low-frequency a rhythmicity, in conjunction with a widespread and marked increase of coherence among high- and low-frequency oscillations. T hese data indicate the presence of a thalamocortical dysrhythmia, which we propose is responsible for all the above mentioned conditions. This coheren t a activity, the result of a resonant interaction between thalamus and cor tex, is due to the generation of low-threshold calcium spike bursts by thal amic cells. The presence of these bursts is directly related to thalamic ce ll hyperpolarization, brought about by either excess inhibition or disfacil itation. The emergence of positive clinical symptoms is viewed as resulting from ectopic gamma-band activation, which we refer to as the "edge effect. " This effect is observable as increased coherence between low- and high-fr equency oscillations, probably resulting from inhibitory asymmetry between high- and low-frequency thalamocortical modules at the cortical level.