The brain integrates new information through the formation of memories and by
learning. Alternative explanations of the ability of the brain to remodel in
response to experience, called plasticity, are given. This item explores those
explanations.Consider the interaction of these three cell types that integrate
information to produce a response to external cues:
\(\begin{array}{|}\hline & {\text { Generic muscle cell }} \\ \hline
\end{array}\)
\(\begin{array}{|}\hline & {\text { Generic neuron }} \\ \hline \end{array}\)
\(\begin{array}{|}\hline & {\text { Generic sensory cell }} \\ \hline
\end{array}\)
A. Use the figure to construct a representation of the direction of
information flow. The central body of a neuron is elaborated by tree-like
structures called dendrites. These allow the neuron to integrate information
from multiple sensory receptors.
B. Describe what refinement of the basic stimulusresponse system in the
diagram is needed to achieve even the simplest response: 鈥渕ove away.鈥�
Awareness of orientation and motion within a body is called proprioception.
Describe how multiple neurons are required to acquire proprioception.
The generation of neurons occurs during development. However, adults continue
to form memories and learn. Rearrangement of connections between neurons is a
possible explanation and in several studies steroid hormones have been shown
to produce dendritic plasticity. The hippocampus is active during memory
formation and learning and significant variations in the number of dendrites
were observed in the hippocampus (Wooley et al., Journal of Neuroscience, 10,
1990) were correlated with variations in estrogen during the estrus cycle.
More recently variation in these structures is implicated in a collection of
behaviors known as chronic unpredictable mild stress (CUMS). In rats CUMS can
be induced by environmental factors such as electric shock, immobilization, or
isolation (Qiao et al., Neural Plasticity, 2016).
C. Pose two scientific questions that can be investigated to connect the
dynamic homeostasis and survival advantage of the individual to dendritic
plasticity.
An alternative explanation of the manner in which the brain integrates new
information is through synaptic plasticity. This has been demonstrated by
Nabavi and coworkers (Nature, 511, 2014). An associated memory was created in
a rat by pairing two stimuli: an audio tone and a foot shock. The animal had
previously been trained to avoid pressing a lever that delivers a reward by
associating the lever press with a shock. After conditioning the animal
responded to the tone as if it was a shock and avoided reward. The ratio of
stimulatory to inhibitory receptors at the synaptic membrane was shown to
increase with the experience.
A miniaturized device, optically activated and controlled by flashing light,
was inserted in the nuclei of neurons transmitting the tone to the rat鈥檚
brain. When the experimenters used light with 1 flash per second (1 Hz) the
device caused the expression by the cell of one type of protein and when a
light with 100 flashes per second (100 Hz) was used the device caused
expression of another type of protein. Each of the graphs describe the
response of the rat to environmental cues. One day elapsed between each data
collection represented by one graph.
D. Analyze these data in terms of the evidence provided for synaptic
plasticity. A third explanation for the formation of memory and learning is
found in the lab of David Glanzman (Elife, 2014). The sea slug (Aplysia) can
be trained to withdraw its siphon tube. Sensory and motor neurons can be grown
in tissue culture. The addition of serotonin to the tissue culture increases
the number of synaptic connections and the training can be induced in vitro.
Cells that had acquired the stimulus-response behavior were treated with an
agent that destroys the synaptic receptors. Yet the trained response was
retained and there were indications that the information was retrieved from
the neuron nucleus.
E. Suppose that this work concerning the location of memory is confirmed.
Create a representation of information flow in which a fourth box labeled
鈥渘euron nucleus鈥� is added to the diagram in part A between the stimulus and
the neuron. Annotate the representation to indicate the flow of information.
Explain Pose questions regarding the ethical or social consequences of this
technology.
鈥� how this form of plasticity is more dynamic than theories in which memory
resides in synaptic or dendritic structures, and
鈥� how it might lead to a treatments for disorders, such as post-traumatic
stress syndrome, in which recollection creates a disability
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