For animals to survive, they must interact with their environment, taking in sensory information and making appropriate motor responses. Early on during vertebrate evolution, this was accomplished with neural circuits located mostly within the spinal cord and brainstem. As the cerebral cortex evolved, it provided additional and powerful advantages for assessing environmental cues and guiding appropriate responses. Importantly, the cerebral cortex was added onto an already functional nervous system. Moreover, every cortical area, including areas traditionally considered sensory, provides input to the subcortical motor structures that are bottlenecks for driving action. These facts have important ramifications for cognitive aspects of motor control. Here we consider the evolution of cortical mechanisms for attention from the perspective of having to work through these subcortical bottlenecks. From this perspective, many features of attention can be explained, including the preferential engagement of some cortical areas at the cost of disengagement from others to improve appropriate behavioral responses.
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