Dominant limb motor impersistence associated with callosal disconnection

Bringing order to higher order motor disorders

Majority of movements in everyday situations are complex and involve volition, planning of the movement and selection of the motor programme, all occurring before movement execution. Higher order motor disorders may be defined as abnormal motor behaviours resulting from disruption of any of the cortical processes that precede execution of the motor act. They are common in patients with neurodegenerative disorders, psychiatric diseases and structural brain lesions. These abnormal behaviours may be overlooked in the clinic, unless specifically evoked by the examiner. We discuss clinical and pathophysiological aspects of higher order motor disorders including: (1) disorders of disinhibition, such as grasp reflex and grasping behaviour, utilisation and imitation behaviour, motor preservations and paratonia; (2) disorders of motor intention such as motor neglect and motor impersistence; (3) alien limb syndrome; and (4) motor overflow phenomena, such as mirror movements and synkinesias. A video illustration of each phenomenon is provided. We place the findings from recent neurophysiological studies within the framework of theories of motor control to provide better insight into pathophysiology of different disorders.

Callosal Motor Impersistence: A Novel Disconnection Syndrome

Motor impersistence, an inability to sustain a certain position or movement, is a motor-intentional disorder, caused more often by right than left hemisphere lesions. Since the right hemisphere is dominant for mediating motor persistence, callosal lesions that disconnect the left hemisphere from the right may induce impersistence of the right upper and lower limbs. After an undiagnosed left callosal infarction, a 65-year-old right-handed man suddenly developed a transient loss of volitional movement of his left leg. Five days after onset, he was admitted to our hospital with signs of callosal disconnection: left-hand agraphia and apraxia, left-hand tactile anomia, failures on cross-replication of hand postures, and intermanual conflict. He had neither weakness nor ataxia of his upper or lower extremities, but when asked to keep his arms or legs extended he could not maintain his right arm and leg in the extended position, suggesting motor impersistence in his dominant limbs. When we examined him 3 months after onset, the motor impersistence had disappeared. In conclusion, motor impersistence of dominant limbs can result from isolated callosal injury that disconnects the left hemisphere from the right hemisphere's frontal-subcortical networks.

Effects of aging on action-intentional programming

BACKGROUND

Action-intentional programs control "when" we initiate, inhibit, continue, and stop motor actions. The purpose of this study was to learn if there are changes in the action-intentional system with healthy aging, and if these changes are asymmetrical (right versus left upper limb) or related to impaired interhemispheric communication.

METHODS

We administered tests of action-intention to 41 middle-aged and older adults (61.9 ± 12.3 years).

RESULTS

Regression analyses revealed that older age predicted a decrement in performance for tests of crossed motor response inhibition as well as slower motor initiation with the left hand.

CONCLUSION

Changes in action-intention with aging appear to be related to alterations of interhemispheric communication and/or age-related right hemisphere dysfunction; however, further research is needed to identify the mechanisms for age-related changes in the brain networks that mediate action-intention.

Dominance specific visual extinction associated with callosal disconnection

Callosal disconnection signs are closely related to asymmetric hemispheric specialization of cognitive functions. Although extinction is more commonly associated with the right parietotemporal lesion, it may occur following lesions of the corpus callosum. After an infarction involving the left splenium, a 58-year-old right-handed man had no disconnection symptoms that had been reported earlier, but showed visual extinction with left or right visual hemifield dominant stimuli. Our results suggest that dominance specific visual extinction might be another disconnection sign associated with splenial lesion.