Abnormal cortex-muscle interactions in subjects with X-linked Kallmann's syndrome and mirror movements.

X-linked Kallmann's (XKS) subjects, who display mirror movements, have abnormal corticospinal tracts which innervate motoneurons of the left and right distal muscles of the upper limb. The size of the abnormal ipsilateral projection is variable. We have used coherence and cumulant analysis between EEG and first dorsal interosseous muscle (1DI) EMG to explore mechanisms underlying mirror movements in three XKS subjects. Results are compared with those of three normal subjects. We argue that significant coherence is functionally relevant when associated with a negative cumulant at an appropriate lag. Given this, normal subjects showed coherence at approximately 22 Hz between the EEG recorded over the sensori-motor cortex contralateral to the voluntarily moved hand and the 1DI EMG of this hand. No significant coherence was seen between 1DI EMG and the sensori-motor cortex ipsilateral to the muscle activity. In contrast, two of the XKS subjects (K2 and K4) had significant coherence at 22 Hz, together with a negative cumulant at an appropriate lag, between the ipsilateral cortical EEG and the 1DI EMG of the voluntarily activated hand. This implies that activity in the abnormal ipsilateral corticospinal projection can contribute to the voluntary drive. For these two subjects, the ipsilateral corticospinal projection was greater than the contralateral projection, as revealed using magnetic brain stimulation. In one of these subjects, K4, significant 22 Hz coherence and negative cumulant was also seen between the EMG of the voluntarily activated hand and the cortex contralateral to this hand. In the third subject, K4a, coherence and negative cumulant was detected between the EMG of the voluntary side and the cortical activity contralateral to this hand. The contralateral cortico spinal projection of this subject was greater than the ipsilateral projection. Regarding the mirroring hand of the XKS subjects, coherence (with negative cumulant at an appropriate lag) was seen in all three subjects between the EMG recorded from the mirroring hand and cortical EEG ipsilateral to this hand. This provides evidence that activity in the aberrant ipsilateral projection is involved in producing the drive that results in mirror movements. In one subject, K4, coherence and negative cumulant was also seen between the EMG of the mirroring hand and motor cortical activity contralateral to this hand. Thus, in this subject, activity in the corticospinal projection contralateral to the mirroring hand also contributed to the mirror movements. In conclusion, this study has provided further evidence that the 22 Hz coherence seen between EEG and EMG is dependent upon corticospinal activity and has furthered our understanding of mechanisms underlying mirror movements.