Title: The Role of Feedback in Early Visual Processing
Author: Alessandra Angelucci
Affiliation: University of Utah, USA.
In the primate cortex, information travels along feedforward connections and is in turn modulated by feedback connections from higher- to lower-order areas. Feedback has been implicated in many important functions for vision, yet it remains poorly understood. We have used viral and optogenetic approaches to investigate the anatomy and function of feedback connections between the marmoset monkey V1 and V2. We find evidence for the existence of multiple anatomically and functionally distinct feedback channels. Moreover, our results point to a fundamental role of feedback in early visual processing, regulating the visual system sensitivity to image features, by controlling response gain, its ability to localize them in space, by controlling RF size, and increasing their coding efficiency, by increasing surround suppression.
Title: Complex Visual Processing in Subcortical Visual Pathways
Author: Natalie Zeater
Affiliation: University of Sydney, Australia
It is traditionally thought that complex visual processes (including binocular responses, orientation selectivity and direction selectivity) only begin to emerge at the level of the visual cortex. Here we describe cells recorded in the marmoset lateral geniculate nucleus and other subcortical nuclei showing cortical-like visual responses.
Title: Two-photon Ca Imaging in the Marmoset Cortex
Author: Tetsuo Yamamori
Affiliation: RIKEN Brain Science Institute, Japan.
This presentation will cover the RIKEN-developed approach for two photon Ca imaging in the marmoset cortex using a tTA/Tre amplification system with AAV vectors. It will include recent data in the marmoset visual cortex using 2-photon Ca imaging.
Title: Motion Sensitivity of MT Cells after V1 Lesions
Author: Maureen Hagan
Affiliation: Monash University, Melbourne, Australia.
Damage to the primary visual cortex (V1) results in a scotoma in the corresponding parts of the visual field. However, both humans and monkeys retain some unconscious visual faculties, or “blindsight”, within the scotoma, presumably via pathways that bypass V1. The motion-sensitive, Middle Temporal Area (MT) is thought to mediate blindsight, as MT neurons respond to stimuli inside the scotoma following V1 lesions. Using moving, random dot stimuli, we found that fewer MT cells were direction selective after V1 lesions compared to control subjects. However, a significant proportion of non-direction cells were tuned to the speed of moving stimuli and titrated their firing rates to the coherence of motion, similar to direction selective cells. This suggests that while direction selectivity is impaired after V1 lesions, motion processing is preserved, even in non-direction selective cells. The decreased proportion of directionally selective cells may explain the compromised global motion perception in these same patients. However, the preserved motion sensitivity in some cells suggest that these cells may be recruited through training to recover global motion discrimination inside the scotoma.
Title: Motion Estimation in the Common Marmoset
Author: Jake Yates
Affiliation: University of Rochester, USA.
The middle temporal area (MT) of the primate brain plays a causal role in the perception of motion. Studies of MT in the macaque have advanced our understanding of neural population coding and perceptual decision making, however, due to its location inside a sulcus, MT in the macaque is inaccessible to large-scale array recordings and imaging techniques. The common marmoset is a New World primate that shares similar organization of MT, but due to its smooth cortex it offers unparalleled access to study large populations of neurons. Here I will describe behavioral performance of two marmoset monkeys performing a continuous motion estimation task. Combined with large-scale recording techniques, this behavioral paradigm offers a new means for studying the neural population code that underlies motion perception.