title: Brain representation of hemifield stimulation in poststroke visual field defects.
abstract: OBJECTIVE
  Plasticity in extended, parallel, or reciprocal operating networks is well recognized. Changes in neuronal activity after lesions to distinct localized structures, such as the primary visual cortex, are less well characterized. We investigated the cortical reorganization in patients with poststroke visual field defects using blood oxygen level-dependent functional MRI.
  
  
  METHODS
  Brain activation was measured in 7 patients with a single occipital cortical lesion and partially recovered hemianopia and in 7 age-matched control subjects. Differences in activation between rest and visual hemifield stimulation were assessed with statistical parametric mapping (SPM'99).
  
  
  RESULTS
  In normal subjects, significant activation was found in the contralateral primary visual cortex and bilaterally in the extrastriate cortex. During hemifield stimulation of the unaffected side of stroke patients, a similar pattern was found compared with that seen in control subjects. During stimulation of the hemianopic side, bilateral activation was seen within the extrastriate cortex, stronger in the ipsilateral hemisphere. The primary visual cortex was not significantly activated in either hemisphere during stimulation of the hemianopic side.
  
  
  CONCLUSIONS
  Visual field defects after stroke are associated with bilateral activation of the extrastriate visual cortex. This pattern of activation indicates altered neuronal activity in the visual system. Further investigation is necessary to determine the relationship between functional reorganization and recovery of lost visual function after poststroke hemianopia.
authors: Neurologisches Therapiezentrum Essen, University of Essen, Essen, Germany. gereon.nelles@uni-essen.de
authors: Gereon
authors: G
authors: Nelles
authors: Guido
authors: G
authors: Widman
authors: Armin
authors: A
authors: de Greiff
authors: Anette
authors: A
authors: Meistrowitz
authors: Albena
authors: A
authors: Dimitrova
authors: Johannes
authors: J
authors: Weber
authors: Michael
authors: M
authors: Forsting
authors: Joachim
authors: J
authors: Esser
authors: H Christoph
authors: HC
authors: Diener
mesh_terms: D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity; D001921:Brain / Q000098:blood supply* / Q000503:physiopathology*; D001931:Brain Mapping; D002560:Cerebrovascular Circulation; D003626:Data Display; D005260:Female; D005403:Fixation, Ocular; D007839:Functional Laterality; D006423:Hemianopsia / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009778:Occipital Lobe / Q000098:blood supply / Q000503:physiopathology; D010775:Photic Stimulation / Q000295:instrumentation / Q000379:methods; D012016:Reference Values; D012146:Rest; D020521:Stroke / Q000150:complications / Q000175:diagnosis*