What are some of the traditional questions and answers that have
been provided in the past.
All of the questions Dudai askes on pgs 8-10 fall into these two catagories
.
B. Where is memory stored? Physiological-Does not tell us about
how memory is stored but can tell us something about what areas or the
brain are responsible for various cognitive functions. Thus, from an analysis
of the nature of a patients mental disorder we can pinpoint the area that
is responsible and begin some sort of remedial treatment.
The earliest record of this question having been addressed comes from
the 4th century BC where Aristotle held that the heart was the seat
of mental function. While this view held for some time mostly on the reputation
of Aristoltle himself it was fundumentally wrong and was challanged first
by Alexandrian anatomists who suggested that mental function might be localized
in the brain and then by the physician Galen (2nd century AD). He
came to this conclusion throught the discection and observation of animals.
Galen seems to be the first person to demonstrate that nerves originate
in the brain and that motor and sensory function are abolished by brain
injuries. **While Galen was correct about the general location he
was very mistaken about the specifics. He believed that nutrients from
food were taken to the liver and converted to 'animal spirits'. These spirits
were then transported throughout the body along the veneous system. The
arteries on the otherhand transported 'vital spirits' formed in the left
ventricle. These vital spirits were converted to 'animal spirits' in the
rete mirabile which was located at the base of the brain and stored in
the ventricles. These animal spirits were stored in the ventricles
and then transported throughout the body through nerves ( which were assumed
to be hollow) when needed.
Medieval scholars attributed even more emphasis to the role of the
ventricles. St Augustus writes that the ventricles were, not only the place
where 'animal spirits' were stored but also the seat of all mental function.
Furthermore, each ventricle was assigned a particular function. The
lateral ventricle was called the 1st cell and it **stored sensory imput
and therefore was in charge of perception. The third ventricle was called
the 2nd cell and it reflected on info recieved from the 1st cell and therefore
was in charge of thinking and reason. The fourth ventricle was called the
3rd cell and served the function of memory. In Dudai it is suggested
that the idea of memories being stored in the ventricles was first proposed
by Costa ben Luca 9th century and Albert Magnus 13th century.
While it may be true that they made the prediction, as you've heard these
midevil scholars were simply rehashing an old idea. Renaissance anatomoists
discovered the errors in the accepted dogma of the time. The demonstrated
that there was no rete mirabile in primates (Vesalius). They also showed
that the ventricles were simply filled with liquid and were too comple
to serve the suggested function (Leonardo Da Vince - cast of cow ventricles).
In the early 1600s Descartes suggested that human memory was
subserved by physical traces in the brain that were produced by activity-dependent
facilitation of connections in these traces (pg 11 Dudai). He did not however
suggest where exactly these traces resided and he was still incorporating
the idea of fluid in the ventricles being involved in the process. IN the
17th century William Harvey's demonstration of how blood flows and is separate
from other fluds helped dispell the belief that ventricular fluidds were
made of converted vital spirits. Furthermore, advances in understanding
that nerves functioned by electrical means helped to clear up the role
of nerves in controlling movement through hydrolic means (carrying animal
spirits to the muscle) - Luigi Galvani, Allesandro Volta.
Support for the storage of memories in the gray matter came from reports
by various surgeons in the late 1800's. Theodule Ribot in France
(1882), Sergei Korsakoff in Russia (1887) and J. Hughlings Jackson
(1888) were some of those who reported that damage to the hippocampal region
was associated with profound deficits in the ability to learn.
At the same time much information on the microscopic aspects of the
nervous system were being published. Golgi demonstrated the the nervous
system was like a net. From his histological studies he suggested that
the brain was made up of a large continuous web (retularis school). Using
slightly modified techniques Ramon y Cajal provided evidence to suggest
that the brain was not one big continuous mass of threadlike tenbdrils
but that it was made up of smaller discrete cells just like the rest of
the body. These discrete cells were connected to each other by dense contacts.
Latter Sir Charles Sherrington would name these contacts 'synapses' **.
In the mid 1900's Sir henry Dale and Otto Loewi would show that transmission
across synapses is chemical.
Sept 8
Also in the mid 1900's Penfield's (1948 ) work with epileptic
patients demonstrated that stimulation of certain areas of the brain could
evoke specific memories. These recollections were produced by stimulation
of areas near those which the neurosurgeons had shown to be important for
learning.
**Karl Spencer Lashley (1950 ) added to the debate by showing
that rats who learned a complex maze were unimpaired in their ability to
renegotiate the maze even after large areas of the brain were removed.
Thus he argued against Penfield's claims of memory localization at least
of complex learning (not simple learning which could be disrupted by localized
lesions in the sensory cortices. He argued forsomething called equipotentiality
and mass action. Both concepts developed to explain the fact that the size
of the cortical lesion was more disruptive than the position of the lesion.
More recent work, that we will review, pinpoints various structures as being important. And shows that the importance of that structure is very specific to the task and question that is being asked. Furthermore, we will reconcile the claims of equipotentiality and localization reported by Lashley and Penfield.
C. How do we form memories? Cognitive
Descarte
Sechenov/Pavlov (1862)- specific principles temporal and spatial
relationships between stimulus and responses are necessary before learned
associations can occur. Some of the most prominent early ideas come from
philosophers. eg Hobbes - associationist
1900 French psychologist Alfred Binet exposed children to various
objects and then tested their memories in the presence or absence of misleading
questions. Binet found that misleading questions produced systematic distortions
in children's recollections. Thus, suggesting that retrieved memory is
not necessarily an imprint of the input but either 1 )distorted during
the storage process, 2) distorted during the retrieval process or 3) both.
In any case the retrieved memory is not an exact replica of reality. Suggesting
that some reconstruction is occurring.
Ramon Y Cajal (1900) demonstrated that the brain was made of
discrete entities he called neurons that seemed to touch each other. Based
on this finding he suggested that changes in those areas of contact would
be responsible for the storage of information i.e. memories.
Thorndike/Skinner - (1900) ibid
Janet (1928) suggested that new experiences are encoded with
respect to, and incorporated into, preexisting knowledge structures accordingly,
individual experience may be very difficult to retrieve later as separate,
distinct entities (Janet - French psychologist)
Bartlett (1932) stated, based on changes in the retelling of
a story, that memories are imaginative reconstruction of past events that
are heavily influenced by the rememberer's prexisting knowledge structures
of schemas. This view was overlooked in favor of the stimulus-response
paradigms and the hypothesis that those paradigms produced (see pavlov,
thorndike)
Hebb (1949)- recapitulated Descartes + Ramon Y Cajal's ideas
by saying that a trace is layed down through repeated activation of that
trace but he extended this by saying that those traces are formed of distributed
assemblies of interconnected neurons thus incorporating the ideas of Lashley.
Seriel processing of information was simulated in computers but found
lacking because these programs were unable to even complete a rather simple
task that is done by humans without even thinking. However, the recent
development of techniques for implimenting parallel distributed processes
on computers have suggested that this may be an important feature of how
memories are stored. This finding lends credence to the Karl Lashleys ideas
of equipotentiality and mass action.
Also,Bartlett's original idea of constructivism or memory reconstruction
are being revisited due to recent evidence and theories that focus on parallel
distributed networks.
Memories are formed in the context of all the information that is available
both externally and internally. When memories are formed in isolation we
have a deficiet referred to as :source amnesia". Again suggesting
that memory is encoded with respect to prior knowledge and other events.
However, sometimes distortions or what is recalled can be very insightful
with respect to how information is stored. Specific errors may be similar
in sound or in context to the word that was to be remembered. This suggests
that when testing what was learned we must be careful to analyze even mistakes
or else we are in danger of missing important information about the way
memories are stored. This is the whole point behind the memory distortion
book.
In reading the texts and listening to lectures you need to keep in
mind that this course, although limited in scope to learning and memory
could just as easily be called animal behavior or intelligence.
In order to forewarn you. I would like to point our a few areas and
questions that I will not be addressing.
Social or collective memory
Forgetting except in passing
Attention or focusing
Summary:
Definition of learning
Levels of analysis