Cortico-cortical feedback connections are abundant yet poorly understood. While many theoretical models incorporate feedback to explain cortical processes, and feedback has been implicated in psychiatric disorders such as schizophrenia, few physiological experiments have rigorously tested the functional effects of feedback. The studies to date offer inconsistent results, which include response facilitation or response suppression when feedback was removed. Typically, these studies have treated all cells in a brain area as identical, ignoring vast anatomical and physiological evidence that shows different layers within a single region have different connections and response properties. In my experiments, I will record in the primary visual area (V1) of alert animals, to test whether the different results found are not contradictory but instead can be explained by feedback's distinct effect(s) on separate layers. I will use permanently implanted cooling chips to inactivate the middle temporal area (MT), an area known to process visual motion and have feedback connections with V1. In addition to layer specificity, I will test whether feedback from MT is involved in the suppressive surround of V1 neurons, particularly in direction selective cells. This idea stems from our lab's previous research showing that orientation tuned V1 cells' surrounds are influenced by feedback from the 2nd and 3rd visual areas (V2/V3). Lastly, I will test whether direction-selective end-stopping, which has been proposed to aid in object motion detection, is due to feedback from MT. These experiments will increase our knowledge of the sources of cells' tuning properties and of cortical function in general.
Despite its implicated involvement in psychiatric diseases such as schizophrenia, feedback from one cortical area to the other has received little attention from experimentalists. The goal of the proposed research is to gain a deeper understanding of feedback by reversibly inactivating one higher-tier brain area, which acts as a source of feedback, while rigorously measuring neuronal activity in the feedback recipient brain area. A thorough understanding of the effects of feedback in cortical processing will allow us to better define its role in healthy humans and in patients suffering from neuropsychiatric disease.
| 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 |
