title: Influence of 'feedback' signals on spatial integration in receptive fields of cat area 17 neurons.
abstract: 'Feedback' signals from mammalian extrastriate visual cortices are reported to exert primarily an excitatory influence on the classical receptive field (CRF) of neurons in the primary visual cortex (V1). However, given the much larger CRFs of neurons in extrastriate visual cortices it is not yet understood how feedback signals influence the spatial integration of visual signals by V1 neurons. To investigate this, we reversibly inactivated one of the 'form-processing' extrastriate visual cortices, the postero-temporal visual (PTV) cortex, and examined changes in responses of V1 neurons to drifting grating patches up to 28 degrees in diameter. We found that during inactivation of PTV cortex the magnitude of the responses to CRF-confined stimuli and that to large stimuli inducing maximum suppression (i.e. minimum responses) was significantly reduced, while the spatial extent of the CRF remained largely unaffected. As a result, the relative strength of the surround suppression increased marginally. This effect was apparent in both simple and complex cells. It was also strong and consistent in cells located in supragranular and infragranular layers. For those cells exhibiting some relief from surround suppression or 'counter-suppression' when large stimuli patches were applied, the effect on counter-suppression was heterogeneous. Overall, the relative integrated responses to the 28 degrees grating patches were also decreased when PTV cortex was inactivated. Thus, a substantial reduction in the CRF response and the largely unaffected spatial extent of the CRF as well as a weak surround effect observed in the present study are consistent with a multiplicative scaling effect.
authors.affiliation: School of Medical Sciences and Bosch Institute, Sydney Node of ARC Centre of Excellence in Vision Science, The University of Sydney, NSW, Australia. chunw@anatomy.usyd.edu.au
authors.forename: Chun
authors.initials: C
authors.lastname: Wang
authors.forename: Jin Yu
authors.initials: JY
authors.lastname: Huang
authors.forename: Cedric
authors.initials: C
authors.lastname: Bardy
authors.forename: Thomas
authors.initials: T
authors.lastname: FitzGibbon
authors.forename: Bogdan
authors.initials: B
authors.lastname: Dreher
mesh_terms: D000818:Animals; D002415:Cats; D025461:Feedback, Physiological / Q000502:physiology*; D005260:Female; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D013028:Space Perception / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*