03 September 1999
Of mice and men
Researchers may have used genetics to improve the memory of mice,
but it is nonsense to talk of an 'intelligence gene', argues Dr Stuart
Derbyshire
Teams of researchers from Princeton University, New Jersey, and
another from the University of Tokyo have discovered improved memory
and learning ability in two strains of genetically modified mice. The
results have caused much excitement, with some commentators talking
about an 'intelligence gene' - raising the possibility of enhancing the
normal intelligence of 'other mammals', including humans.
But while this work is undoubtedly a step towards enhancement of
some of the basic information-processing capacities that all mammals
share, it is still a long stretch from these studies to a facilitation of
human memory, let alone intelligence.
Memory in humans and all other mammals is intricately tied in with a
piece of the brain called the hippocampus. If you were to be so unlucky
as to lose your hippocampus on both sides of your brain, you would
never again be able to place an event into long-term memory. Memories
never develop beyond the moment of hippocampal destruction and the
patient forever lives in the past and immediate present.
Knowing this important site for memory, researchers have turned
their attention towards the mechanisms of the hippocampus. This is
what the current studies investigated. It is known that information is
shuffled around and maintained inside the hippocampus dependent upon
the properties of receptors (sites at which actions take place) and their
interaction with neurotransmitters (chemicals that allow communication
between receptor sites). The important receptor is NMDA and the
important neurotransmitter is glutamate. When NMDA binds to
glutamate a current is evoked which opens a channel allowing calcium
ions to enter the cell. This is the magical moment when the cells of the
hippocampus talk in harmony and strengthen their connections, known
technically as long-term potentiation (LTP) and more commonly as the
beginning of memory. The researchers at Princeton hoped to improve the
memory of mice through the increase of an NMDA subtype that has an
extended LTP - while the researchers in Tokyo deleted the genetic
code for a non-NMDA hippocampal receptor that inhibits LTP, thereby
inadvertently extending overall LTP.
Both groups demonstrated improved memory in their transgenic
strains through a standard behavioural test. The mice were released into
a shallow pool of water and swam around until stumbling across a
hidden platform and standing on it. This was done on multiple occasions
and the time taken to reach the platform was recorded. All the mice
reached the platform more quickly on later trials, indicating learning.
The transgenic mice, however, performed better than the normal mice,
showing further improved learning due to the genetic manipulation.
So will we be able to create humans with super memories? Perhaps. I
have no doubt that humans and mice share important properties relating
to the hippocampus and its basic function. But even so, memory in mice
and memory in humans are far removed. Simple associative learning -
discovering that A follows B, etc - is an aspect of memory and, if you are
a mouse surviving from one moment to the next, it might be terrific to
have your associative learning enhanced. But humans do not survive in
this manner - we have developed ourselves and our society and can
operate on a more general, abstract level. Being able to understand
connections between A and B might be a prerequisite for abstract
memories but that does not mean a better recognition of concrete
relationships will improve abstract memory. It might even be
detrimental. Humans use memory in a transformative manner to go
beyond simple relationships and to develop abstract connections.
The ability to draw abstract relationships and pursue meaningful
goals is the hallmark of human intelligence that is sorely lacking in the
mouse world - even in the newly created super mouse world. In the
mouse, memory is merely an extension of their basic biological function
with zero intelligent content. Our intelligence remains under the
influence of basic information-processing skills (as evidenced by its
severe compromising when processing is lost to dementia), but
intelligence is more than the simple additive effects of processing
environmental associations. For humans, memory is not a natural
extension of biology but is a part of the transformation and
interweaving of innate biological processes into higher intelligent
function.
The transformation of our biological information-processing capacity,
which we share with mice, takes place in the sociocultural world, which
we do not share with mice. During development, formal schooling and
other cultural interventions, the subordination of biological instinct to
volitional control is nurtured and encouraged. Memory ceases to be
slavishly dictated by internal and external events and becomes a tool
that can be used in the pursuit of reasoned goals. A genetic and neural
influence can remain, but the cause of intelligence lies outside of
genetics and pharmacology.
Dr Stuart Derbyshire is head of neuro-imaging at the Neuroenteric
Disease Program, University of California in Los
Angeles
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