The annual Cosyne meeting provides an inclusive forum for the exchange of experimental and theoretical/computational approaches to problems in systems neuroscience.
Title: A Dendritic Mechanism for Dynamic Routing and Control in the Thalamus
Authors: Subutai Ahmad, Carmen Varela
A prevalent hypothesis about the thalamus is that thalamocortical cells (TC) function as ‘gated relays’, switching between two different modes of response (burst and tonic) controlled by modulators such as the corticothalamic input from layer 6 (L6). Predictive theories of perception and cognition model neocortical feedback as carrying expectations generated by learned models of the world. However, few predictive coding hypotheses consider the implications of corticothalamic (CT) feedback to thalamus, despite the fact that this is an integral component of the neocortical circuit, and despite the fact that the number of feedback CT axons is an order of magnitude greater than feedforward TC axons. Here we propose a dendritic mechanism by which L6 corticothalamic cells could exert precise contextual modulatory control over thalamic activity. A calcium mediated plasticity rule enables TC cells to detect precise sparse codes from L6 on dendrites in a branch specific manner. We describe how the dendrite specific mechanism enables TC cells to act as a flexible multiplexer, a shifter, or a contextual filter. If L6 feedback encodes a location signal, the thalamic circuit can implement spatial and contextual selective attention mechanisms. The proposed mechanism closely matches the detailed anatomy and physiology of thalamocortical circuits, and leads to specific experimentally testable hypotheses. We suggest that L6 corticothalamic feedback enables the thalamus to support complex routing operations that are far more powerful than traditionally assumed.