study of patients in early, drug-naive stages showed an increase in alpha band (8-10 Hz) cortico-cortical functional connectivity that expanded toward other frequency bands (4-30 Hz range) with increasing disease severity.101 Increased connectivity affected both global and local connections and was associated with motor deficits.100,101 Less clear is whether levodopa administration and deep brain stimulation normalise these abnormalities, as one study showed a normalization of connectivity after intervention in association with motor improvement,100 and another showed a further increase in connectivity.99 In PDD, preliminary studies indicate a different pattern, with decreased functional connectivity reminiscent of the changes in AD.102 In DLB, the most consistent finding is a reduction of global cortico-cortical coherence in the alpha (8-13Hz) frequency band.103-105 A MEG study specifically assessed coherence in long (anterior and posterior) and short (lateral and medial) cortico-cortical connections, reporting more pronounced loss of connectivity in long- than short-distance connections in this frequency band.103 Inconsistent changes have been reported in the delta (0·5-4Hz) frequency range.104,105
