of cell division and labeling, whereas the previously mentioned procedures are only useful for short-term quantification. Viral vectors It has recently become more common to use recombinant viruses to insert the genetic information encoding specific markers (usually protein fluorophores such as GFP) that are only expressed in cells of a certain kind. The marker gene is inserted downstream of a promoter, leading to transcription of that marker only in cells containing the transcription factor(s) that bind to that promoter. For example, a recombinant plasmid may contain the promoter for doublecortin, a protein expressed predominantly by neurons, upstream of a sequence coding for GFP, thereby making infected cells fluoresce green upon exposure to light in the blue to ultraviolet range while leaving non doublecortin expressing cells unaffected, even if they contain the plasmid. Many cells will contain multiple copies of the plasmid and the fluorphore itself, allowing the fluorescent properties to be transferred along an infected cell's lineage. By labeling a cell that gives rise to neurons, such as a neural stem cells or neural precursor cells, one can track the creation, proliferation, and even migration of newly created neurons. It is important to note, however, that while the plasmid is stable for long periods of time, its protein products may have highly variable half lives and their fluorescence may decrease as well as become too diluted to be seen depending on the number of round of replication they have undergone, making this method more useful for tracking self-similar neural precursor or neural stem cells rather than neurons themselves. The insertion of genetic material via a viral vector tends to be sporadic and infrequent relative to the total number of cells in a given region of tissue, making quantification of cell division inaccurate. However, the above method can provide highly accurate data with respect to when a cell was born as well as full cellular morphologies. Methods for inhibiting neurogenesis Many studies analyzing the role of adult neurogenesis utilize a method of inhibiting cell proliferation in specific brain regions, mimicking an inhibition of neurogenesis, to observe the effects on behavior. Pharmacological inhibition Pharmacological inhibition is widely used in various studies, as it provides many benefits. It is generally inexpensive as compared to other methods, such as irradiation, can be used on various species, and does not require any invasive procedures or surgeries for the subjects. However, it does pose certain challenges,