Hockenbury Discovering Psychology 5th txtbk

A Guided Tour of the Brain65First, research by psychologistElizabeth Gould and her colleagues(1998) showed that adult marmosetmonkeys were generating asignificant number of new neuronsevery day in the hippocampus, abrain structure that plays a criticalrole in the ability to form newmemories. Gould’s groundbreakingresearch provided the first demonstrationthat new neurons could developin an adult primate brain.Could it be that the human brainalso has the capacity to generatenew neurons in adulthood?Researchers Peter Eriksson, FredGage, and their colleagues (1998)provided the first evidence that itdoes. The subjects were five adultcancer patients, whose ages rangedfrom the late fifties to the early seventies.These patients were all beinggiven a drug used in cancer treatmentsto determine whether tumorcells are multiplying. The drug is incorporated into newly dividing cells, coloringthem. Using fluorescent lights, this chemical tracer can be detected in the newly createdcells. Eriksson and Gage reasoned that if new neurons were being generated,the drug would be present in their genetic material.Within hours after each patient died, an autopsy was performed and the hippo -campus was removed and examined. The results were unequivocal. In each patient,hundreds of new neurons had been generated since the drug had been administered,even though all the patients were over 50 years old (see accompanying photo). Theconclusion? Contrary to the traditional scientific view, the human brain has the capacityto generate new neurons throughout the lifespan (Eriksson & others, 1998;Kempermann & Gage, 1999).As new research on neurogenesis has exploded, new findings—and new questions—have arisen (Sahay & Hen, 2007). For example, Gould and her colleagues have foundthat new neurons develop and migrate to multiple brain regions in adult macaque monkeys(see Gould, 2007). Stress, exercise, environmental complexity, and even socialstatus have been shown to affect the rate of neurogenesis in rodents, birds, and monkeys(see Gage & others, 2008). It is nowgenerally accepted that newborn neuronsdevelop into mature functioning neurons inat least two regions of the human brain—the hippocampus, involved in learning andmemory, and the olfactory bulb, responsiblefor odor perception. And, it appears thatthese new neurons are incorporated into theexisting neural networks in the adult humanbrain (Gage, 2003; Lledo & others, 2006).In the next section, we’ll begin ourguided tour of the brain. Following thegeneral sequence of the brain’s development,we’ll start with the structures at thebase of the brain and work our way up tomore complicated brain regions, whichare responsible for complex mental activity.Elizabeth Gould: Challenging ScientificDogma After earning her psychologydoctorate at UCLA, Gould investigated theeffect of stress hormones on rats. In theprocess, she found evidence of the developmentof new neurons in the rats’ brains,a discovery that, if true, contradicted scientificunderstandings at that time. Herresearch eventually showed that neuro -genesis takes place in the adult brains ofmany species, from rats to primates. Today,Gould’s research in her Princeton Universitylab focuses on the effects of environmentaldeprivation and enrichment on the mammalianbrain (Lehrer, 2006). You can visitGould’s Princeton lab at: http://www.princeton.edu/~goulde/index.htmlNeurogenesis in the Adult Human BrainUsing laser microscopes to examine sectionsof the adult hippocampus, researchersPeter Eriksson and Fred Gage (1998) documentedthe presence of new neurons,shown in green, amid already establishedneurons, shown in red. In the area of thehippocampus studied, each cubic centi -meter of brain tissue contained from 100to 300 new neurons. Research on adultmice has shown that the newly generatedneurons develop into fully functionalneurons that form synaptic connectionswith existing cells in the hippocampus(van Praag & others, 2002).