05.2020 | THE SCIENTIST 45CREDIT LINE
The study from Cameron’s lab on rats’ ability to shift their
attention grew out of the researchers’ work on stress, in which
they observed that rodents sometimes couldn’t switch from
one task to the next. Turning again to the literature, Cam-
eron found a study from 1969 that seemed to suggest that
neurogenesis might affect this task-switching behavior. Her
team set up the water bottle experiments to see how well rats
shifted attention. Inhibiting neurogenesis in the adult mice
led to a 50 percent decrease in their ability to switch their
focus from drinking to searching for the source of the sound.
“This paper is very interesting,” says J. Tiago Gonçalves, a neu-
roscientist at Albert Einstein College of Medicine in New York
who studies neurogenesis but was not involved in the study. It
could explain the findings seen in some behavioral tasks and the
incongruences between findings from different behavioral tasks,
he writes in an email to The Scientist. Of course, follow-up work
is needed, he adds.
Cameron argues that shifting attention may be yet another
behavior in which the hippocampus plays an essential role but
that researchers have been overlooking. And there may be an
unexplored link between making new neurons and autism or
other attention disorders, she says. Children with autism often
have trouble shifting their attention from one image to the next
in behavioral tests unless the original image is removed.It’s becoming clear, Cameron continues, that neurogene-
sis has many functions in the adult brain, some that are very
distinct from learning and memory. In tasks requiring atten-
tion, though, there is a tie to memory, she notes. “If you’re not
paying attention to things, you will not remember them.” gReferences- C.S.S. Weeden et al., “A role for hippocampal adult neurogenesis in shifting
attention toward novel stimuli,” Behav Brain Res, 376:112152, 2019. - J. Altman, “Are new neurons formed in the brains of adult mammals?” Science,
135:1127–28, 1962. - P.S. Eriksson et al., “Neurogenesis in the adult human hippocampus,” Nat Med,
4:1313–17, 1998. - E. Gould et al., “Proliferation of granule cell precursors in the dentate gyrus of
adult monkeys is diminished by stress,” PNAS, 95:3168–71, 1998. - A. Sahay et al., “Increasing adult hippocampal neurogenesis is sufficient to
improve pattern separation,” Nature, 472:466–70, 2011. - C.K. Toner et al., “Visual object pattern separation deficits in nondemented
older adults,” Learn Mem, 16:338–42, 2009. - M.A. Yassa et al., “Pattern separation deficits associated with increased
hippocampal CA3 and dentate gyrus activity in nondemented older adults,”
Hippocampus, 21: 968–79, 2011. - N. Toni et al., “Synapse formation on neurons born in the adult hippocampus,”
Nat Neurosci, 10:727–34, 2007. - K.M. McAvoy et al., “Modulating neuronal competition dynamics in the
dentate gyrus to rejuvenate aging memory circuits,” Neuron, 91:1356–73, 2016. - K.G. Akers et al., “Hippocampal neurogenesis regulates forgetting during
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DO NEW NEURONS APPEAR ANYWHERE ELSE IN THE BRAIN?
Many, though not all, neuroscientists agree that there’s ongoing neurogenesis in the hippocampus of most mammals, including humans. In
rodents and many other animals, neurogenesis has also been observed in the olfactory bulbs. Whether newly generated neurons show up any-
where else in the brain is more controversial.
There had been hints of new neurons showing up in the striatum of primates in the early 2000s. In 2005, Heather Cameron of the
National Institute of Mental Health and colleagues corroborated those findings, showing evidence of newly made neurons in the rat neo-
cortex, a region of the brain involved in spatial reasoning, language, movement, and cognition, and in the striatum, a region of the brain
involved in planning movements and reacting to rewards, as well as self-control and flexible thinking (J Cell Biol, 168:415–27). Nearly a
decade later, using nuclear-bomb-test-derived carbon-14 isotopes to identify when nerve cells were born, Jonas Frisén of the Karolinska
Institute in Stockholm and colleagues examined the brains of postmortem adult humans and confirmed that new neurons existed in the
striatum (Cell, 156:1072–83, 2014).
“Those results are great,” Cameron says. They support her idea that there are different types of neurons being born in the brain
throughout life. “The problem is they’re very small cells, they’re very scattered, and there’re very few of them. So they’re very tough to
see and very tough to study.”Aging humans, in whom neuro-
genesis is thought to decline, often
have trouble remembering details
that distinguish similar experiences.