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Beyond Animal Research
By Aysha Akhtar, M.D., M.P.H. May
2006 |
Neurological Experiments: Monkey See...But Not Like Humans
Rhesus (or macaque) monkeys are some of the most common animals
used in neurological experiments concerning the visual system. Here
are some recent examples of such experiments:
- At the University of Connecticut, electrodes were screwed into
monkeys’ brains, the monkeys were strapped into restraining
devices, and then they were trained to perform visual tasks, often
involving electrical stimulation.1
- At the University of California, Davis, the brains of monkeys
were surgically exposed and then directly injected with acid to
destroy certain areas. The monkeys were then studied for visual
learning skills.2
- At Columbia University, monkeys were implanted with scleral
coils (electrical wires inserted into the eyes), head restraint
devices, and recording chambers. Their eye movements were then
recorded.3
Often, monkeys are deprived of food and water and then rewarded
with these basic necessities. In addition to the fact that these and
other similar experiments cause enormous stress and pain for the
monkeys, they have little or no clinical usefulness.
Monkeys are used extensively in neurological experiments because
of the assumption that they, out of all animal species, are most
neurologically similar to humans. But how similar are they? The
human brain is far more complex in architecture and physiology than
the monkey brain. One indication of this is the length of time it
takes for the brain to develop in its major phase: 136 days
for monkeys and 470 days for humans.4 Here are a few of
the many more specific examples of how the two species differ in
neuroanatomy and neurophysiology:
- The human cortex has 10 times the surface area of that of a
monkey.5
- The V 1 area (one of the predominant visual areas in the
brain) makes up 10 percent of the total cortex in monkeys and only
3 percent of the total cortex in humans.6
- Similar visual areas perform very different functions in
humans and monkeys.7, 8
- The number of synapses—or connections—a human neuron makes is
between 7,000 and 10,000. In the rhesus monkey, that number is
between 2,000 and 6,000.4
- The expression of at least 91 genes involved in a variety of
neural mechanisms differ between monkeys and humans.9
- Humans have visual processing areas that do not exist in
monkeys.10
As one primate researcher stated, “the human brain …is more than
simply a large monkey or ape brain.”11 Undoubtedly,
similarities exist in primate and human neurophysiology. However,
given the advances in medicine today, the differences between
species is far more important than the similarities. Technology has
given researchers the ability to examine the nuances of
physiological mechanisms in order to specifically target an
intervention, such as a drug to boost or inhibit a specific cellular
process. For this, we need the most accurate possible information
about the neurological system of humans – not monkeys.
Researchers can study human neurology in an ethical
manner. Many clinical centers use imaging and neurophysiologic tools
to map and monitor the human visual and other neurological systems.
Centers such as Princeton University, the University of Chicago, the
University of Pennsylvania, and Minnesota State University use
functional MRIs, PET scans, and evoked potentials (which record the
brain’s electrical patterns) to collect relevant data on human
neural processing and anatomy.12-15 With these and many
more wonderful tools available for noninvasive study of the human
brain, we can most effectively help patients who suffer from
neurological diseases.
References 1. Cromer JA,
Waitzman DM. Neurones associated with saccade metrics in the monkey
central mesencephalic reticular formation. J Physiol.
2006;570.3:507-523. 2. Lavenex PB, Amaral DG,
Lavenex P. Hippocampal lesions prevent spatial relational learning
in adult macaque monkeys. J Neurosci.
2006;26(17):4546-4558. 3. Ipata AE, Gee AL,
Goldberg ME, Bisley JW. Activity in the lateral intraparietal area
predicts the goal and latency of saccades in a free-viewing visual
search task. J Neurosci. 2006;26(14):3656-3661.
4. Dehaene S, Duhamel J-R, Hauser MD, Rizzolatti
G. From monkey brain to human brain: A Fyssen foundation symposium.
Cambridge, MA: MIT Press, 2005: 83 5. Dehaene S,
Duhamel J-R, Hauser MD, Rizzolatti G. From monkey brain to human
brain: A Fyssen foundation symposium. Cambridge, MA: MIT Press,
2005: 3. 6. Dehaene S, Duhamel J-R, Hauser MD,
Rizzolatti G. From monkey brain to human brain: A Fyssen foundation
symposium. Cambridge, MA: MIT Press, 2005: 9. 7.
Dehaene S, Duhamel J-R, Hauser MD, Rizzolatti G. From monkey brain
to human brain: A Fyssen foundation symposium. Cambridge, MA: MIT
Press, 2005: 277 8. Tootell RBH, Mendola JD,
Hadjikhani NK, et al.. Functional analysis of V3A and related areas
in human visual cortex. J. Neurosci.
1997;17:7060-7078 9. Caceres M, Lachuer J, Zapala
MA, et al. Elevated gene expression levels distinguish human from
non-human primate brains. PNAS.
2003;100(22):13030-13035. 10. Vanduffel W, Fize D,
Peuskens H, et al. Extracting 3D from motion: Differences in human
and monkey intraparietal cortex. Science.
2002;298:413-415 11. Dehaene S, Duhamel J-R,
Hauser MD, Rizzolatti G. From monkey brain to human brain: A Fyssen
foundation symposium. Cambridge, MA: MIT Press,
2005:41. 12. McKeeff TJ, Tong F. The timing of
perceptual decisions for ambiguous face stimuli in the human ventral
visual cortex. Cereb Cortex. 2006. April 28 (Epub ahead of
print). 13. Phan KL, Britton JC, Taylor SF, Fig
LM, Liberzon I. Corticolimbic blood flow during nontraumatic
emotional processing in posttraumatic stress disorder. Arch Gen
Psychiatry. 2006;63(2):184-192. 14. Newberg
AB, Wang J, Rao H, et al. Concurrent CBF and CMRGlc changes during
human brain activation by combined fMRI-PET scanning.
Neuroimage. 2005;28(2):500-506. 15. Page
JW, Findley J, Crognale MA. Electrophysiological analysis of the
effects of ginkgo biloba on visual processing in older healthy
adults. J Gerontol A Biol Sci Med Sci.
2005;60(10):1246-1251. |