Learning and synapsis plasticity

[Quixix]

I am rather confused on this subject. As I understand, learning or memory formation is mainly achieved by synaptic plasticity. I don't think that reinforcing should achieve any learning. Also, I believe that most new synapsis or connections are formed as the result of associative inputs, that is, a connection is strengthened when activated simultaneously with an already active synapsis. Therefore, can a new stimulus that isn't related to the activation of any previous connections lead to new knowledge?

Pau

[badchad]

Also look into a phenomenon called "long term potentiation" which is also used as a model of learning.

 

As for everything else, I'm not sure what you mean by "I don't think reinforcing should achieve any learning".

 

And lastly, it seems intuitive to think that a "new stimulus not related to the activation of any previous connections" would result in learning. At some point in our lives, every stimulus we encountered was essentially "new". How would we have learned anything otherwise?

[Quixix]

Also look into a phenomenon called "long term potentiation" which is also used as a model of learning.

 

As for everything else' date=' I'm not sure what you mean by "I don't think reinforcing should achieve any learning".

 

And lastly, it seems intuitive to think that a "new stimulus not related to the activation of any previous connections" would result in learning. At some point in our lives, every stimulus we encountered was essentially "new". How would we have learned anything otherwise?[/quote']

 

What ifsomething is intuitive thinking or not? I love intuitive and speculative thinking; I am not postulating any new discovery or writing about any scientific paper

.

LTP is basically a mechanism that increases post synapsis response by repeated or strong pre synapsis stimulus. I would think of that as reinforcing, but it involves a neuron and connections that already ract to a given pre synaptic stimulus. It could be conceived as a part of learning, but to my way of thinking it is hardly so.

I would tend to interpret real learning as the formation of new synaptical connections or activations. Synapsis that "learn" to activate the neuron and create a post synaptic reaction, by being activated simultaneously with a strong signal to another synapsis. In this way, the synapsis whose stimulus was previously not significant enough to produce post synaptic firing, becomes strong and its firing becomes capable of producing the post synaptic firing.

Pau

[nettron]

Appears what you are referring to is Hebbian learning which is really just a primitive form of learning at the single neuron level. Hebb postulated that "when an axon of cell A is near enough to excite cell B or repeatedly or consistently takes part in firing it, some growth or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased."

 

Pavlov was on a similar track with his dog experiments, a form of classical conditioning involving the repeated presentation of food while ringing a bell. The dog would eventualy associate the ringing of the bell with food and would salivate. Again a very basic form of learning....believe adaption is another.

 

I think the "real learning" you are referring to, be it cognitive or motor, would be far more involved than this. Think about the first time you tried to ride a bike or read a book. I'd say learning at this level would require a complex interplay of various neuron assemblies that each follow some ,as yet, unknown "rules" for synaptic modification. The purkinje cells of the cerebellum is a good example.

 

http://www.robotic.dlr.de/Smagt/research/cerebellum/cerebellum.html

[BrainMan]

As I understand, learning or memory formation is mainly achieved by synaptic plasticity.

 

The term "synaptic plasticity" doesn't explain anything at all. You would be better off thinking of the term as an advertisement for research than as a scientific term. [it has no agreed upon meaning. It is mostly just a codeword for "changes occur" without any specification of what those chages are, on what level they occur, why they occur, and what they do.]

[Quixix]

The term "synaptic plasticity" doesn't explain anything at all. You would be better off thinking of the term as an advertisement for research than as a scientific term. [it has no agreed upon meaning. It is mostly just a codeword for "changes occur" without any specification of what those chages are, on what level they occur, why they occur, and what they do.]

I am sorry to completely disagree with you, that is I and several professional researchers and authors. The way many of those changes occur have been extensively studied and published, as well as the results of such changes.

[Quixix]

Appears what you are referring to is Hebbian learning which is really just a primitive form of learning at the single neuron level. Hebb postulated that "when an axon of cell A is near enough to excite cell B or repeatedly or consistently takes part in firing it' date=' some growth or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased."

 

Pavlov was on a similar track with his dog experiments, a form of classical conditioning involving the repeated presentation of food while ringing a bell. The dog would eventualy associate the ringing of the bell with food and would salivate. Again a very basic form of learning....believe adaption is another.

 

I think the "real learning" you are referring to, be it cognitive or motor, would be far more involved than this. Think about the first time you tried to ride a bike or read a book. I'd say learning at this level would require a complex interplay of various neuron assemblies that each follow some ,as yet, unknown "rules" for synaptic modification. The purkinje cells of the cerebellum is a good example.

 

http://www.robotic.dlr.de/Smagt/research/cerebellum/cerebellum.html[/quote']

 

Interesting site. Shall have to study it with more time.

Since the time that Hebbs proposed his theory, many advances have been achieved.

I agree that learning any little matter must involve groups of neurons, complete circuits, some operatingalmost synchronously. But learning can occur at two levels, implicit (unconscious )and explicit (conscious).

I think riding a bike belongs to implicit, yet, the fact that several (millions) of neurons, would not change the fact that plasticity, formation and reinforcement of synapsis, is involved.

[BrainMan]

I am sorry to completely disagree with you, that is I and several professional researchers and authors. The way many of those changes occur have been extensively studied and published, as well as the results of such changes.

 

But no specific change falls under the term "synaptic plasticity" and no one agrees upon what it means exactly. Microbiologists almost inevitably use the term very differently from psychologists, for example. If you try to publish a paper and are using the term "synaptic plasticity", Im quite sure reviews will want you to be more specific and say exactly what you mean.

 

Don't give me that "I and several professional researchers" crap. I'm tied close enough to the area to know what is going on...

[Quixix]

But no specific change falls under the term "synaptic plasticity" and no one agrees upon what it means exactly. Microbiologists almost inevitably use the term very differently from psychologists' date=' for example. If you try to publish a paper and are using the term "synaptic plasticity", Im quite sure reviews will want you to be more specific and say exactly what you mean.

 

Don't give me that "I and several professional researchers" crap. I'm tied close enough to the area to know what is going on...[/quote']

 

Here is somemore "crap" :

This in an excerpt from LeDoux:(The Chronicle of Higher Education

December 11, 1998)

"One of the most important contributions of modern neuroscience has been to show that the nature/nurture debate operates around a false dichotomy: the assumption that biology, on one hand, and lived experience, on the other, affect us in fundamentally different ways. Research has shown that not only do nature and nurture each contribute (in disputable proportions) to who we are, but also that they speak the same language. Both achieve their effects by altering the synaptic organization of the brain.

 

Synapses are the connection points between brain cells that allow the cells to communicate with each other. Synapses are responsible for much of the brain's activity. The particular patterns of synapses in a person's brain, and the information that those connections encode, are the keys to who that person is.

 

We are born with a hefty dose of preprogrammed synaptic links -- this is why we can cry and wriggle around the moment we leave the womb. But experience alters synapses as well, either creating new ones or changing the strength of existing ones. Our ability to see the world the same way other humans do is programmed in us. But unless we have the right kinds of visual experiences at the right time, synapses in the visual system of the brain won't develop normally and, as a result, we will not see normally. For example, if a child's eyes are misaligned during a certain period in early life, the brain's visual system is deprived of depth cues and depth perception is impaired.

 

The process by which experience shapes synapses is referred to as "synaptic plasticity." Although a great deal of synaptic plasticity occurs during early childhood as the brain is developing, plasticity in the form of learning and memory continues to shape our synapses throughout our lives.

 

We are used to thinking of memory in terms of our ability to consciously recall past events. Recent advances in neuroscience and psychology have revealed that this explicit memory -- sometimes called declarative memory -- is only one of many forms of memory. Various other kinds are implicit, which is to say that they work unconsciously. They are what enable us to learn skills as diverse as how to ride a bike or play the piano, as well as to avoid stimuli previously associated with pain or danger.

 

Damage in the part of the brain that controls explicit memory can prevent you from remembering when you learned to ride a bike, for example, but not your ability to ride it. Damage to your implicit memory can interfere with your ability to ride but not your memory of having learned how."

This article is six years old. MOre progress has been made since.

[BrainMan]

The process by which experience shapes synapses is referred to as "synaptic plasticity."

 

Boy is that specific. *rolls eyes in duisgust*

 

 

 

 

 

But thanks for making my point for me!

[nettron]

I agree that the terms "synaptic plasticity" is a rather no-brainer, its like saying plastercine (clay?) is malleable. According to the liturature, its well known and has bin proven experimentally that synapses are modifiable.

 

Im assuming what we're getting at here is what and when. To be more specific; what biological "rules" account for synaptic modification and when do these rules come into play?

 

Although Hebb's postulate ('49?) didnt account for depression and has bin broadened into todays LTD and LTP, seams rather sad if this is all we have.

 

Or is there more to syncrony than one would think. To use the Cerebeller purkinje cells that i had alluded to earlier as an example; its believed that when the climbing fiber is active, only those parallel fibers that are active at the same time( or during some short time window) will cause their corresponding synapses to be facilitated. This speaks volumes for syncrony but tells us nothing about why this should occur at that particular time, after all we dont want to learn everything...only those things that are significant.

 

The theories of David Marr and James Albus shed some light on it suggesting that the climbing fiber inputs are the training signals that "fine-tune" the motor programs from the neo-cortex from which they originate. This fine-tuning then appears to be accomblished via sensory feedback and stored motor programs( a look-up table?) so that actions can be both adjusted on-the-fly and predicted before the action is even completed.

 

The odd thing about all this is that the output from the Cerebellum is strictly inhibitory ( puts the brakes on ) unto the deep Cerebeller nuclei.

 

Guess this either raises eyebrows or just raises more questions