The functional role of corticogeniculate feedback in visual perception
Although much is known about transformations in visual information that occur in feedforward circuits connecting the retina to the visual thalamus (the dorsal lateral geniculate nucleus or LGN) to the primary visual cortex (V1), relatively little is known about the functional contributions of the first feedback circuits in the visual system, corticogeniculate circuits. Corticogeniculate neurons provide an anatomically robust, but physiologically weak or modulatory input onto relay neurons in the LGN. In spite of decades of study, the function of corticogeniculate feedback in visual perception has remained a stubborn puzzle. Our goal is to resolve this puzzle using methods to selectively and reversibly manipulate corticogeniculate neurons in highly visual animal models. We have demonstrated that corticogeniculate neurons in carnivores and primates are physiologically and morphologically distinct and organized into parallel processing streams that match the feedforward parallel streams present in these species. Furthermore, using a virus-mediated gene-delivery strategy and optogenetics, we show that corticogeniculate feedback improves the temporal precision of LGN neuronal responses to visual stimuli, as well as the spatial resolution of some LGN neuronal responses, in carnivores and primates. Improvements in temporal precision are accompanied by reductions in LGN neuronal response variability and increases in the information coding capacity of LGN neurons when corticogeniculate feedback is optogenetically enhanced. Our current work is aimed at further examining corticogeniculate influence on LGN activity during visual behavior and employing novel methods such as functional ultrasound imaging combined with optogenetics to explore the influence of corticogeniculate feedback on population responses in the LGN.
Dr. Farran Briggs is a Senior Investigator of the Thalamocortical Visual Processing Section at NIH/NEI.
Dr. William Hodos NACS Seminars are free and open to the public.
