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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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