Hyperexcitatory activity in visual cortex in homonymous hemianopia after stroke.
OBJECTIVE
Damage to and destruction of neural afferents result in a disruption of sensory input, which causes reduced activity in the corresponding cortical areas. Conversely, there is also evidence that lesions in the sensory pathway induce changes in the intracortical connectivity resulting in augmented cortical activity due to disinhibition. As disinhibition is assumed 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 visual cortex were studied using magnetoencephalography. In order to compare the neural activity affected by the lesion with the activity associated with 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 activity 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 cortical disinhibition induced by lesions in the visual system. Furthermore, the possible role of cortical disinhibition as a basis for cortical reorganization and as a precondition for the recovery of impaired visual functions is discussed.
Braun
C
C
Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Otfried-Müller-Strasse 47, 72076, Tübingen, Germany. christoph.braun@uni-tuebingen.de
Weber
J
J
Schiefer
U
U
Skalej
M
M
Dietrich
T
T
D006423:Hemianopsia / Q000209:etiology* / Q000503:physiopathology*; D006801:Humans; D015225:Magnetoencephalography; D009433:Neural Inhibition; D010775:Photic Stimulation; D012607:Scotoma / Q000209:etiology / Q000503:physiopathology; D020521:Stroke / Q000150:complications*; D014793:Visual Cortex / Q000503:physiopathology*