Coordination of Actions and Habits in the Medial Prefrontal Cortex of Rats
Cerebral Cortex. 2003-04-01; 13(4): 400-408
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1. J Neurophysiol. 2014 Nov 15;112(10):2413-22. doi: 10.1152/jn.00476.2014. Epub
2014 Aug 13.
Radial-tangential anisotropy of crowding in the early visual areas.
Kwon M(1), Bao P(2), Millin R(2), Tjan BS(3).
(1)Schepens Eye Research Institute/Massachusetts Eye and Ear Infirmary, Boston,
Massachusetts; and Department of Ophthalmology, Harvard Medical School, Boston,
(2)Neuroscience Graduate Program, University of Southern California, Los Angeles,
(3)Department of Psychology, University of Southern California, Los Angeles,
California; Neuroscience Graduate Program, University of Southern California, Los
Angeles, California; .
Crowding, the inability to recognize an individual object in clutter (Bouma H.
Nature 226: 177-178, 1970), is considered a major impediment to object
recognition in peripheral vision. Despite its significance, the cortical loci of
crowding are not well understood. In particular, the role of the primary visual
cortex (V1) remains unclear. Here we utilize a diagnostic feature of crowding to
identify the earliest cortical locus of crowding. Controlling for other factors,
radially arranged flankers induce more crowding than tangentially arranged ones
(Toet A, Levi DM. Vision Res 32: 1349-1357, 1992). We used functional magnetic
resonance imaging (fMRI) to measure the change in mean blood oxygenation
level-dependent (BOLD) response due to the addition of a middle letter between a
pair of radially or tangentially arranged flankers. Consistent with the previous
finding that crowding is associated with a reduced BOLD response [Millin R, Arman
AC, Chung ST, Tjan BS. Cereb Cortex (July 5, 2013). doi:10.1093/cercor/bht159],
we found that the BOLD signal evoked by the middle letter depended on the
arrangement of the flankers: less BOLD response was associated with adding the
middle letter between radially arranged flankers compared with adding it between
tangentially arranged flankers. This anisotropy in BOLD response was present as
early as V1 and remained significant in downstream areas. The effect was observed
while subjects’ attention was diverted away from the testing stimuli. Contrast
detection threshold for the middle letter was unaffected by flanker arrangement,
ruling out surround suppression of contrast response as a major factor in the
observed BOLD anisotropy. Our findings support the view that V1 contributes to
Copyright © 2014 the American Physiological Society.
PMID: 25122703 [Indexed for MEDLINE]