title: Displacement of sensory maps and disorganization of motor cortex after targeted stroke in mice.
abstract: OBJECTIVE
  Recovery from stroke is hypothesized to involve the reorganization of surviving cortical areas. To study the functional organization of sensorimotor cortex at multiple time points before and after stroke, we performed longitudinal light-based motor mapping of transgenic mice expressing light-sensitive channelrhodopsin-2 in layer 5 cortical neurons.
  
  
  METHODS
  Pulses of light stimulation were targeted to an array of cortical points, whereas evoked forelimb motor activity was recorded using noninvasive motion sensors. Intrinsic optical signal imaging produced maps of the forelimb somatosensory cortex. The resulting motor and sensory maps were repeatedly generated for weeks before and after small (0.2 mm3) photothrombotic infarcts were targeted to forelimb motor or sensory cortex.
  
  
  RESULTS
  Infarcts targeted to forelimb sensory or motor areas caused decreased motor output in the infarct area and spatial displacement of sensory and motor maps. Strokes in sensory cortex caused the sensory map to move into motor cortex, which adopted a more diffuse structure. Stroke in motor cortex caused a compensatory increase in peri-infarct motor output, but did not affect the position or excitability of sensory maps.
  
  
  CONCLUSIONS
  After stroke in motor cortex, decreased motor output from the infarcted area was offset by peri-infarct excitability. Sensory stroke caused a new sensory map to form in motor cortex, which maintained its center position, despite becoming more diffuse. These data suggest that surviving regions of cortex are able to assume functions from stroke-damaged areas, although this may come at the cost of alterations in map structure.
authors.affiliation: Department of Psychiatry, Brain Research Centre, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Harrison
authors.forename: Gergely
authors.initials: G
authors.lastname: Silasi
authors.forename: Jamie D
authors.initials: JD
authors.lastname: Boyd
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Murphy
mesh_terms: D000818:Animals; D001931:Brain Mapping / Q000295:instrumentation / Q000379:methods*; D000075402:Channelrhodopsins; D005260:Female; D005552:Forelimb / Q000502:physiology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009044:Motor Cortex / Q000473:pathology / Q000503:physiopathology*; D009473:Neuronal Plasticity / Q000502:physiology; D009474:Neurons / Q000648:ultrastructure; D061848:Optical Imaging / Q000379:methods; D012886:Skull / Q000601:surgery; D013003:Somatosensory Cortex / Q000473:pathology / Q000503:physiopathology*; D020521:Stroke / Q000139:chemically induced / Q000473:pathology / Q000503:physiopathology*; D013997:Time Factors
chemical_list: D000075402:Channelrhodopsins
keywords: brain mapping; cerebral cortex; mice; motor cortex; neuronal plasticity; somatosensory cortex