Model approach to neurological variants of visuo-spatial neglect.

Neglect is a neurological disorder of spatial attention with reduced awareness of visual stimuli in the hemifield contralateral to an acute temporo-parietal lesion mainly of the right hemisphere. There is a close association of multisensory orientation centers (MSO) and vestibular tonus imbalance. A lesion of the dominant right MSO causes a left-sided neglect due to a lack of ipsilateral activation of the visual cortex, which is further enhanced by increasing inhibition from the contralateral visual cortex. The nondominant MSO in the left hemisphere might be involved in the manifestation of the less frequent and more transient right-sided neglect and in the plastic mechanisms of gradual recovery from left-sided neglect or extinction. There is evidence that a vestibular tonus inbalance due to peripheral or central vestibular pathway lesions may also induce a neglect. In a first model approach using an attractor network and assuming that there is only one MSO in the right hemisphere, it is possible to simulate attentional shifts into a visual hemifield and to induce a neglect. The neural network model consists of four layers of neurons: retina, MSO, visual cortex V1, and superior colliculus. The superior colliculus layer is modeled as a recurrent attractor network with one inhibitory interneuron and synaptic weights chosen to implement a winner-take-all network that centers the hill of activity on the strongest input. We are well aware of the simplifications used in the conceptual drawings and the computational model, but nevertheless hope that they will serve as an inspiration for further modeling and clinical studies.