The ubiquity of cortico-cortical feedback connections argues strongly for their importance, and theoreticians routinely make use of them in models of cortical function. Despite this, next to nothing is known about their function. Previous studies in which feedback has been manipulated have been performed in anesthetized animals, and our recent studies in alert animals have revealed fundamentally different results. Our major finding from the previous cycle is that feedback from V2 exerts minimal effects on the classically defined receptive field center of V1 neurons: orientation tuning and the center's contrast response function are virtually unaffected. However, larger stimuli that engage the receptive field surround and that normally cause suppression, cause much less suppression when V2 is inactivated. We have further discovered that the influence of feedback is on the spatial extent of the surround, rather than on its gain, and that seemingly higher order properties of surround suppression, such as feature- matched suppression, are more strongly influenced by feedback than is basic normalization. All of these observations are consistent with a theoretical framework of predictive coding, which posits a key computational role for the interaction between feedforward and feedback connections. We now propose to examine specific examples ranging from built-in contextual influences in form and motion perception to the nature of changes that underlie the learning of a perceptual task. Our general approach will be to use causal manipulations-reversible inactivation of cortical areas (V2 and/or MT) that feed back to V1-to test the hypothesized role of top-down influences in perceptual inference. Our studies will shed light on the basic mechanisms of cortical function.
This project aims to understand the functional role of cortico-cortical feedback, a failure of which has been implicated in neuropsychiatric disorders that take an enormous toll on human wellbeing in the United States and throughout the world. For example, there is strong evidence that patients with schizophrenia have specific deficits in FB processing, which may account for auditory hallucinations, in which self-generated, internal language (i.e. thinking) is misattributed to an external source (i.e. 'voices'), as well as for mor directly quantifiable measures of top-down, predictive functions, such as the 'size-weight illusion' and the 'hollow mask illusion'. Patients with schizophrenia have been shown to be impaired in psychophysical correlates of surround suppression; this is particularly relevant, because, as described in the proposal, our lab has shown that feedback connections play a critical role in generating surround suppression in the visual cortex.
| Ponce, Carlos R; Hartmann, Till S; Livingstone, Margaret S (2017) End-Stopping Predicts Curvature Tuning along the Ventral Stream. J Neurosci 37:648-659 |
| Hartmann, Till S; Zirnsak, Marc; Marquis, Michael et al. (2017) Two Types of Receptive Field Dynamics in Area V4 at the Time of Eye Movements? Front Syst Neurosci 11:13 |
| Gómez-Laberge, Camille; Smolyanskaya, Alexandra; Nassi, Jonathan J et al. (2016) Bottom-Up and Top-Down Input Augment the Variability of Cortical Neurons. Neuron 91:540-547 |
| Trott, Alexander R; Born, Richard T (2015) Input-gain control produces feature-specific surround suppression. J Neurosci 35:4973-82 |
| Mundell, Nathan A; Beier, Kevin T; Pan, Y Albert et al. (2015) Vesicular stomatitis virus enables gene transfer and transsynaptic tracing in a wide range of organisms. J Comp Neurol 523:1639-63 |
| Ruff, Douglas A; Born, Richard T (2015) Feature attention for binocular disparity in primate area MT depends on tuning strength. J Neurophysiol 113:1545-55 |
| Born, Richard T; Trott, Alexander R; Hartmann, Till S (2015) Cortical magnification plus cortical plasticity equals vision? Vision Res 111:161-9 |
| Smolyanskaya, Alexandra; Haefner, Ralf M; Lomber, Stephen G et al. (2015) A Modality-Specific Feedforward Component of Choice-Related Activity in MT. Neuron 87:208-19 |
| Nassi, Jonathan J; Gómez-Laberge, Camille; Kreiman, Gabriel et al. (2014) Corticocortical feedback increases the spatial extent of normalization. Front Syst Neurosci 8:105 |
| Smolyanskaya, Alexandra; Ruff, Douglas A; Born, Richard T (2013) Joint tuning for direction of motion and binocular disparity in macaque MT is largely separable. J Neurophysiol 110:2806-16 |
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