title: Profiling brain function: spatiotemporal characterization of normal and abnormal visual activation.
abstract: OBJECTIVE
  In clinical neuroscience, the utility of evoked and event-related potentials (EPs and ERPs) resides in the temporal information they provide. However, it is largely unknown whether valuable diagnostic information resides within the corresponding spatial patterns. To determine this, the first step involves testing whether "normal" versus "abnormal" EPs/ERPs can be differentiated based on spatial patterns. In the current study, we present a method that characterizes similarities across individual source maps, called the profile algorithm. The profile algorithm was evaluated in terms of its ability to detect spatial activation differences in myopic individuals with corrected and uncorrected vision. This experiment represents a critical test of the method before applying it to the assessment of perceptual/cognitive functions.
  
  
  METHODS
  Visual-evoked potentials (VEPs) were recorded from healthy subjects using checkerboard stimulation. The N75 and P100 were examined in individuals with corrected (20/20) and uncorrected vision (20/40 or worse).
  
  
  CONCLUSIONS
  N75 and P100 amplitudes and latencies were modulated by vision condition. The profile algorithm differentiated successfully between corrected and uncorrected vision. Its discriminatory power outperformed a more traditional method based on ERP peak amplitude. Subsequent correlations revealed significant relationships between visual impairment and both the components and the spatial activation. Overall, the findings suggested that VEP spatial patterns were sensitive to manipulations of visual acuity.
  
  
  CONCLUSIONS
  The findings demonstrate that EP/ERP spatial activation can be evaluated at the individual level and compared against normative data. Ultimately, the method may provide a valuable tool for assessing individual spatial activation changes in perceptual/cognitive functions.
authors.affiliation: National Research Council Canada, Institute for Biodiagnostics (Atlantic), Halifax, NS, Canada.
authors.forename: Vanessa L
authors.initials: VL
authors.lastname: Versteeg
authors.forename: Yannick
authors.initials: Y
authors.lastname: Marchand
authors.forename: Erin L
authors.initials: EL
authors.lastname: Mazerolle
authors.forename: Ryan C N
authors.initials: RC
authors.lastname: D'Arcy
mesh_terms: D000465:Algorithms; D000704:Analysis of Variance; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D005074:Evoked Potentials, Visual; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors; D014786:Vision Disorders / Q000503:physiopathology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult