Gain Modulation as a Mechanism for Switching Reference Frames, Tasks, and Targets
In the mammalian brain, gain modulation is a ubiquitous mechanism for integrating information from various sources. When a parameter modulates the gain of a neuron, the cell’s overall response amplitude changes, but the relative effectiveness with which different stimuli are able to excite the cell does not. Thus, modulating the gain of a neuron is akin to turning up or down its “loudness”. A well-known example is that of visually sensitive neurons in parietal cortex, which are gain-modulated by proprioceptive signals such as eye and head position. Theoretical work has shown that, in a network, even relatively weak modulation by a parameter P has an effect that is functionally equivalent to turning on and off different subsets of neurons as a function of P. Equipped with this capacity to switch, a neural circuit can change its functional connectivity very quickly. Gain modulation thus allows an organism to respond in multiple ways to a given stimulus, so it serves as a basis for flexible, nonreflexive behavior. Here we discuss a variety of tasks, and their corresponding neural circuits, in which such flexibility is paramount and where gain modulation could play a key role.
KeywordsFiring Rate Receptive Field Coordinate Transformation Hand Position Stimulus Location
Research was partially supported by grant NS044894 from the National Institute of Neurological Disorders and Stroke.
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