Hyperexcitatory activity in visual cortex in homonymous hemianopia after stroke

Objectives: Damage to and destruction of neural afferents result in a disru ption of sensory input, which causes reduced activity in the corresponding cortical areas. Conversely, there is also evidence that lesions in the sens ory pathway induce changes in the intracortical connectivity resulting in a ugmented cortical activity due to disinhibition. As disinhibition is assume d to be involved in the reconfiguration of neural networks, its appearance after brain lesions might be relevant for the restitution of impaired brain functions. Methods: The effects of lesions in the visual pathway on the activity in vi sual cortex were studied using magnetoencephalography. In order to compare the neural activity affected by the lesion with the activity associated wit h intact visual processing, only patients with unilateral, post-chiasmatic lesions resulting in homonymous hemianopia were examined. Results: Stimulation within the scotoma resulted in reduced magnetic activi ty compared to the stimulation of the intact hemifield. Increased activity was observed when the border region of the scotoma was stimulated. Conclusions: It is concluded that the magnetic hyperactivity reflects corti cal disinhibition induced by lesions in the visual system. Furthermore, the possible role of cortical disinhibition as a basis for cortical reorganiza tion and as a precondition for the recovery of impaired visual functions is discussed. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.