Genetic schemes and schemata in neurophysiology.

Information in nervous systems is often carried by neural ensembles--groups of neurons in transient functional linkage--and written in a code that involves the spatial locations of active neurons or synapses and the times at which activity occurs. Even in favorable neuroanatomical circumstances, studying neural ensemble function presents a serious experimental challenge. One recent strategy to overcome this challenge relies on protein-based sensors that provide direct optical images of neural activity, and on protein-based effectors that interfere with it. Because these molecules are encodable in DNA, they can be introduced into intact animals by genetic manipulation, and their expression pattern can be tailored to include--exclusively and at the same time comprehensively--the neurons of interest. Circumscribed populations of neurons can thus be studied in virtual isolation at defined stages of intact neural pathways.