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Linear (F1)NonLinear (F2)
H4405.006
Spatial Phase (Deg)
Firin
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ate
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Nonlinear, non-oriented receptive fields in early visual cortex: Possible precursors to second-order processing
• Neurons selective for the orientation of both luminance (1st order) and contrast (2nd order) boundaries form a considerable proportion in early visual cortex (cat Area 18, macaque V2). • Neural mechanism underlying receptive fields of these neurons is unknown.
• Recent evidence suggests that inputs from LGN Y cells could be pooled together in cortex to build these receptive fields (Rosenberg et al., 2010; Demb et al.,2001). • But nonlinear RFs of Y cells can only signal increase in contrast but not decrease.
• Given this, we hypothesize that there is an intermediate processing stage at the cortical level which provides inhibition to 2nd order responsive neurons.
1Integrated Program Neuroscience, McGill Univ.; 2McGill Vision Res. Unit, Montreal, Canada Amol Gharat1and Curtis Baker2
Methods • Anesthetized, paralyzed cats.
• Extracellular, single-unit recording in Area 18 using 32 channel linear arrays.
• Response measured as average firing frequency for complex cells and 1st & 2nd harmonic modulations for simple cells.
• Manual spike sorting using Plexon Offline Sorter.
Stimulus • Sinusoidal grating.
• Temporal Modulation: Drifting or Contrast reversing.
• .Y like receptive fields of these cortical neurons suggests that they receive input from LGN Y cells. • These neurons could provide an important intermediate stage in building cortical orientation selective second-order neurons
1. Rosenberg et al 2010 2. Demb et al 2001 3. Crook et al 2008
Funded by CIHR grant MA-9685, MOP-119498 to CB. Vanier Canada Graduate Scholarship to AG.
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N = 135
Orientation Bias (OB)
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OB = 0.09 OB = 0.68
H 4303.017 CH 22_1
H 4303.017 CH 31_1
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spontaneous activity
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0.13 cpd
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0.53 cpd
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Fundamental frequency response (4 Hz)
LINEAR (F1)
Frequency doubled response (8 Hz) NON-LINEAR (F2)
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H4505.030 CH28_1
H4505.030 CH21_4
Linear Non-LinearY cell signature
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3707.006
drifting gratingcontrast reversing (F2)Contrast Modulation
Spatial Frequency (cpd)
Firin
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Firing Rate (H
z)
Area 18
Non-Ori
Area 18
Ori
Linear RF Non-Linear RF
Excitatory Inhibitory Excitatory Inhibitory