Zusammenfassung
Higher organisms can establish complex associations between sensory
events and motor responses. More remarkable than their complexity,
however, is that the resulting sensory-motor maps can be selectively
interchanged. For example, a person who speaks English and Spanish
can read aloud "con once, sin once," going effortlessly from one
language to the other. What is the neural basis of this capacity?
Here, a network model is presented in which multiple maps between
sensory stimuli and motor actions are possible, but only one of them,
depending on behavioral context, is implemented at any given time.
The key is a nonlinear representation in which the gain of sensory
responses is regulated by context information. Neuronal responses
can indeed show variations in gain, as has been documented in the
case of proprioceptive signals such as eye and head position, which
can modulate visually triggered activity. However, in contrast to
these, the contextual cues used here need not bear any relationship
to the physical attributes of the stimuli; in particular, spatial
location is irrelevant. The model thus postulates the existence of
sensory neurons that are nonlinearly modulated by arbitrary context
signals, a plausible and testable prediction. The proposed mechanism
allows a network of neurons to effectively change the functional
connectivity between its inputs and outputs and may partially explain
how animals can quickly adapt their behavior to varying environmental
conditions.
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