title: Exploiting individual primary visual cortex geometry to boost steady state visual evoked potentials.
abstract: OBJECTIVE
  The steady-state visual evoked potential (SSVEP) is an electroencephalographic response to flickering stimuli generated partly in primary visual area V1. The typical 'cruciform' geometry and retinotopic organization of V1 is such that certain neighboring visual regions project to neighboring cortical regions of opposite orientation. Here, we explored ways to exploit this organization in order to boost scalp SSVEP amplitude via oscillatory summation.
  
  
  METHODS
  We manipulated flicker-phase offsets among angular segments of a large annular stimulus in three ways, and compared the resultant SSVEP power to a conventional condition with no temporal phase offsets. (1) We divided the annulus into standard octants for all subjects, and flickered upper horizontal octants with opposite temporal phase to the lower horizontal ones, and left vertical octants opposite to the right vertical ones; (2) we individually adjusted the boundaries between the eight contiguous segments of the standard octants condition to coincide with cruciform-consistent, early-latency topographical shifts in pattern-pulse multifocal visual-evoked potentials (PPMVEP) derived for each of 32 equal-sized segments; (3) we assigned phase offsets to stimulus segments following an automatic algorithm based on the relative amplitudes of vertically- and horizontally-oriented PPMVEP components.
  
  
  RESULTS
  The three flicker-phase manipulations resulted in a significant enhancement of normalized SSVEP power of (1) 202%, (2) 383%, and (3) 300%, respectively.
  
  
  CONCLUSIONS
  We have thus demonstrated a means to obtain more reliable measures of visual evoked activity purely through consideration of cortical geometry. This principle stands to impact both basic and clinical research using SSVEPs.
authors.affiliation: Department of Biomedical Engineering, The City College of New York, City University of New York, New York, NY 10031, USA.
authors.forename: M Isabel
authors.initials: MI
authors.lastname: Vanegas
authors.forename: Annabelle
authors.initials: A
authors.lastname: Blangero
authors.forename: Simon P
authors.initials: SP
authors.lastname: Kelly
mesh_terms: D000328:Adult; D000465:Algorithms; D001931:Brain Mapping / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D005425:Flicker Fusion / Q000502:physiology*; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*
references.citation: Clin Neurophysiol. 2011 Jan;122(1):128-33
references.pmid: 20573542
references.citation: J Neurosurg. 1974 Jun;40(6):747-55
references.pmid: 4826600
references.citation: IEEE Trans Biomed Eng. 2005 Sep;52(9):1588-96
references.pmid: 16189972
references.citation: PLoS One. 2012;7(3):e29519
references.pmid: 22412829
references.citation: J Physiol. 1972 Sep;225(2):1P-3P
references.pmid: 5074382
references.citation: Nature. 2003 Jul 17;424(6946):309-12
references.pmid: 12867981
references.citation: Front Hum Neurosci. 2009 Nov 30;3:58
references.pmid: 20011221
references.citation: Clin Neurophysiol. 2008 Feb;119(2):399-408
references.pmid: 18077208
references.citation: Electroencephalogr Clin Neurophysiol. 1979 Apr;46(4):409-15
references.pmid: 85537
references.citation: J Opt Soc Am. 1977 Nov;67(11):1475-89
references.pmid: 411904
references.citation: Neuroimage. 2013 Jan 1;64:703-11
references.pmid: 22982584
references.citation: Exp Brain Res. 1972;16(1):1-21
references.pmid: 4646539
references.citation: J Neurosci Methods. 2004 Mar 15;134(1):9-21
references.pmid: 15102499
references.citation: Expert Rev Med Devices. 2007 Jul;4(4):463-74
references.pmid: 17605682
references.citation: IEEE Trans Neural Syst Rehabil Eng. 2005 Jun;13(2):172-8
references.pmid: 16003896
references.citation: Invest Ophthalmol Vis Sci. 2003 Feb;44(2):879-90
references.pmid: 12556425
references.citation: Hum Brain Mapp. 2007 Apr;28(4):323-34
references.pmid: 16779799
references.citation: Ann Neurol. 2011 Oct;70(4):574-82
references.pmid: 21710621
references.citation: J Vis. 2010 Dec 31;10(14):
references.pmid: 21196511
references.citation: Conf Proc IEEE Eng Med Biol Soc. 2004;2004:4507-10
references.pmid: 17271308
references.citation: Proc Natl Acad Sci U S A. 2010 Aug 3;107(31):13878-82
references.pmid: 20643918
references.citation: Nat Neurosci. 2000 Mar;3(3):259-63
references.pmid: 10700258
references.citation: IEEE Trans Biomed Eng. 1997 Dec;44(12):1243-52
references.pmid: 9401224
references.citation: Nat Neurosci. 2012 Dec;15(12):1729-35
references.pmid: 23103963
references.citation: Clin Neurophysiol. 2002 Jun;113(6):767-91
references.pmid: 12048038
references.citation: Clin Neurophysiol. 2001 Apr;112(4):713-9
references.pmid: 11275545
references.citation: Neuroimage. 2010 Oct 1;52(4):1401-9
references.pmid: 20488247
references.citation: Vis Neurosci. 2009 Mar-Apr;26(2):227-35
references.pmid: 19250600
references.citation: Neuroimage. 2013 Aug 1;76:442-5
references.pmid: 22504764
references.citation: Electroencephalogr Clin Neurophysiol. 1987 Jul;68(4):256-67
references.pmid: 2439305
references.citation: Spat Vis. 1997;10(4):437-42
references.pmid: 9176953
references.citation: Clin Neurophysiol. 1999 Oct;110(10):1793-800
references.pmid: 10574294
references.citation: IEEE Trans Neural Syst Rehabil Eng. 2003 Jun;11(2):137-40
references.pmid: 12899256
references.citation: Clin Neurophysiol. 2010 Dec;121(12):1981-91
references.pmid: 20547470
references.citation: Proc Natl Acad Sci U S A. 1996 May 14;93(10):4770-4
references.pmid: 8643478
references.citation: Spat Vis. 1997;10(4):433-6
references.pmid: 9176952
references.citation: Electroencephalogr Clin Neurophysiol. 1994 Jan;90(1):65-81
references.pmid: 7509275