MIRROR MOVEMENTS IN X-LINKED KALLMANNS-SYNDROME .1. A NEUROPHYSIOLOGICAL STUDY

Possible mechanisms underlying the pathological mirror movements that are seen in the majority of patients with X-linked Kallmann's syndrome have been investigated using neurophysiological techniques. An EMG wa s recorded from the first dorsal interosseous muscle (1DI) during volu ntary self-paced abduction of one index finger; EMG activity could als o be recorded simultaneously from the contralateral 1DI. There was no significant difference between the time of onset of the bursts of volu ntary and involuntary mirroring EMG. Focal magnetic stimulation of the hand area of the motor cortex revealed the presence of fast conductin g bilateral corticospinal projections from each motor cortex in all su bjects. However, both inter- and intra-subject differences exist when considering the ratio of ipsilaterally to contralaterally projecting a xons. Cross-correlation analysis of multi-unit EMGs recorded during si multaneous voluntary sustained activation of homologous left and right pairs of distal upper limb muscles was performed A short duration cen tral peak was seen in the cross-correlograms indicating the presence o f a common drive to left and right homologous motor neuron pools. This common drive may result from the synchronous activation of intermingl ed ipsilaterally and contralaterally projecting corticospinal neurons in the motor cortex. Cutaneomuscular reflexes were recorded from the 1 DI following stimulation of the digital nerves of the index finger. Ty pically each reflex comprises spinal and longer latency trans-cortical components. In these subjects, the long latency components of the ref lex response could, in addition, be recorded from the 1DI of the non-s timulated side. We conclude that these subjects have a novel ipsilater al corticospinal tract and that activity in this tract is responsible, at least in part, for the pathological mirroring.