Changing our neurological fate
How exercise and mental stimulation sharpen our senses and enhance cognitive abilities
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Aging
diminishes our ability to process new information. After a certain
point in our development, the critical period of learning closes off
and our senses become less receptive to stimuli. This is exemplifed by
the remarkable capacity of young children who almost effortlessly pick
up a new language in their infancy, but find it much harder to grasp
the basic concepts of a foreign language in University.
Synaptic plasticity is the ability of
neuronal connections, called synapses, to either strengthen with
increased neural activity, or to diminish when left unused. The loss of
too many individual synaptic connections can lead to deterioration of
important neural pathways—one of the underlying causes of many
neurodegenerative diseases. However, there
may be some hope to influence our ‘fate’ of cognitive decline and to
counter the loss of synaptic plasticity in the brain. Research has
shown that the rate of new neuron formation is enhanced by physical
activity, and that the survival of these new neurons increases when we
are immersed in a constantly challenging environment. How does this work? Exercise
has been shown to increase the rate of long-term potentiation (LTP) in
the synapse, which reinforces connections between neurons within a
particular pathway. Neurons require this constant stimulation and
activity to stay healthy and to prevent degeneration of the neuronal
circuitry. Providing an enriched environment (from, for example,
activities that exercise and stimulate our bodies and minds) allows
newly formed neurons to retain activity and ensures that the new
pathways are maintained. As a result,
any immature newborn granule cells—small underdeveloped precursor
neurons—in the pathway are recruited and incorporated into the
circuitry. Since the survival of mature neurons is activity-dependent,
the firing threshold is lowered, making it easier for the neuron to
become depolarized and excited. This enhances LTP, which ensures that
the neuron will continue to fire and thus strengthen its connections
with neighbouring neurons to reinforce its place in the neural
pathway. This process works in much the same way as the
development of ‘muscle memory’ when we learn to ride a bike, for
example. We start by learning the basic movements with training wheels
and, with practice, we learn to balance ourselves. Without practice and
consistant reinforcement of the motor pathway, learning would not come
as easily.
LTP takes
place primarily in regions of the brain that are constantly being
enriched with new stimuli. These areas include the dentate gyrus in the
hippocampus, which is responsible for memory formation, as well as the
olfactory bulb where new neurons are constantly needed to integrate new
smells and senses into the brain. Recent studies have also reported the
presence of neural progenitor cells in the retina—a finding that could
have implications for people with impaired vision caused by diabetic
retinopathy.
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