Selective Activation of the Deep Layers of the Human Primary Visual Cortex by Top-Down Feedback

Curr Biol. 2016 Feb 8;26(3):371-6. doi: 10.1016/j.cub.2015.12.038. Epub 2016 Jan 28.


In addition to bottom-up input, the visual cortex receives large amounts of feedback from other cortical areas [1-3]. One compelling example of feedback activation of early visual neurons in the absence of bottom-up input occurs during the famous Kanizsa illusion, where a triangular shape is perceived, even in regions of the image where there is no bottom-up visual evidence for it. This illusion increases the firing activity of neurons in the primary visual cortex with a receptive field on the illusory contour [4]. Feedback signals are largely segregated from feedforward signals within each cortical area, with feedforward signals arriving in the middle layer, while top-down feedback avoids the middle layers and predominantly targets deep and superficial layers [1, 2, 5, 6]. Therefore, the feedback-mediated activity increase in V1 during the perception of illusory shapes should lead to a specific laminar activity profile that is distinct from the activity elicited by bottom-up stimulation. Here, we used fMRI at high field (7 T) to empirically test this hypothesis, by probing the cortical response to illusory figures in human V1 at different cortical depths [7-14]. We found that, whereas bottom-up stimulation activated all cortical layers, feedback activity induced by illusory figures led to a selective activation of the deep layers of V1. These results demonstrate the potential for non-invasive recordings of neural activity with laminar specificity in humans and elucidate the role of top-down signals during perceptual processing.

Keywords: laminar fMRI; perceptual inference; predictive coding; shape perception.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Feedback*
  • Female
  • Humans
  • Magnetic Resonance Imaging
  • Male
  • Visual Cortex / physiology*
  • Young Adult