Magno and parvocellular contributions to the cortical visually evoked response – time-frequency and source considerations
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1
Swinburne University of Technology, Centre for Human Psychopharmacology, Australia
Purpose: The search for cortical evoked responses identifiable as magnocellular (M) or parvocellular (P) in origin is heightened by claims for abnormal magno processing in disorders as disparate as Schizophrenia, Autism, Dyslexia and Dyscalculia. However, in human, the readily available techniques of EEG, MEG, fMRI measure different signals with different technology. Nonlinear Wiener kernel analysis of visual evoked cortical potentials (VEP) and magnetic evoked fields (MEF) offer some distinct advantages in isolating M and P generated activity.
Methods: Contrast responses of VEP kernels recorded with 29 normal young adults were compared with Magnetoencephalographic evoked fields (MEF) generated using a similar pseudorandom stimulus developed using a VPixx/DataPIXX combination recorded through the 306 SQUID sensors of an Elekta TRIUX magnetoencephalograph on a (different) population of 15 normal young adults.
Results: Contrast response functions were extracted from the major first and second order Wiener kernel peaks of the VEP. Naka-Rushton fits enabled contrast gain and semi-saturation contrasts to be elicited for each peak. A short latency second order response with high contrast gain and a saturating contrast response function mimicking primate magnocellular (M) responses was found. A longer latency non-linearity (P) with lower contrast gain and no evidence of contrast saturation across the full range of stimulus contrasts was also found. MEG nonlinear analysis yielded similar responses, with the added source localization capability indicating that the earliest cortical responses (~50ms) occurred simultaneously over the occipital pole and an extrastriate location (MT/V5). Time-Frequency MEG analysis differentiates the slices of the second order response, with the putative magno response of the first slice of the second order response showing heightened gamma band activity, while the second slice (K2.2 - putative parvocellular response) shows strong beta band activation but little gamma.
Conclusion: The cortical VEP and MEF first and second order responses can be decomposed into those with high contrast gain and contrast saturation (M-like) versus those with lower contrast gain and little evidence of saturation (P-like). TF analysis demonstrates higher gamma power in the magno components. The latency of the M-like components is approximately 25 ms less than those of the P-like components. Comparison of MEF with cortical VEP results gives strong confirmation of the M and P origins of the first and second slice major peaks respectively.
Acknowledgements
National Health and Medical Research Council NHMRC (APP1004740)
Keywords:
Magnocellular,
Parvocellular pathway,
nonlinearity,
Magnetoencephalography (MEG),
visual evoked potential (VEP)
Conference:
ACNS-2013 Australasian Cognitive Neuroscience Society Conference, Clayton, Melbourne, Australia, 28 Nov - 1 Dec, 2013.
Presentation Type:
Poster
Topic:
Sensation and Perception
Citation:
Crewther
DP,
Hugrass
L,
Brown
A and
Hollis
C
(2013). Magno and parvocellular contributions to the cortical visually evoked response – time-frequency and source considerations.
Conference Abstract:
ACNS-2013 Australasian Cognitive Neuroscience Society Conference.
doi: 10.3389/conf.fnhum.2013.212.00007
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Received:
15 Oct 2013;
Published Online:
25 Nov 2013.
*
Correspondence:
Prof. David P Crewther, Swinburne University of Technology, Centre for Human Psychopharmacology, Hawthorn, VIC, 3122, Australia, dcrewther@swin.edu.au