Morkeliph
02-02-2006, 8:55 PM
Hey, seeing as you're a molecular biologist and all, maybe you can answer this for me. I was talking with my professor the other day about the physiological mechanisms of classical conditioning in animals and humans. I'm not sure how much you deal with respondent conditioning so perhaps first I should explain what I mean by this; hopefully this wont be too lengthy or technical.
I'm going to presume that you already understand the general principle of classical conditioning, US, UR, CS, CR and the like. Extinction, of course, occurs when the CS is presented repeatedly without the US and eventually fails to produce a CR. Spontaneous recovery, as you might know, is when after a period of rest from extinction, the CS is again presented alone and elicits a CR of some magnitude greater than when extinction ended. Additionally, you may remember that second, third and subsequent acquisition trainings occur more rapidly than the first or prior training. Disinhibition occurs when after a CR is extinguished, the CS is presented along with some salient, novel stimulus and the CR is again elicited.
Why am I rehearsing these things to you? Well, it's fairly obvious that extinction training does not "erase" prior aquisition training because the organism is never quite the same afterwards. Spontaneous recovery, disinhibition and rapid reacquisition all show that in some way, the organism is still different from how it was prior to initial conditioning. The general theory behind this is as follows: extinction training is not a "breaking of the US-CS association" but actually the conditioning of a second, inhibitory response. This response is more fragile and more easily disrupted than excitatory responses. It disrupts with time (spontaneous recovery) and deviations from training conditions (disinhibition). In other words, it's similar to a kind of conditioned suppression.
EDIT (FINISHING THE POST): Presumably, if we knew more about the physiology of classical conditioning, as in what physically is going on inside the organism as they learn new conditioned responses, then we might better understand why these events occur. Many studies have shown that when organisms learn new behaviors or responses, nerve growth occurs that actually creates new neural connections. In other words, neurons are making new connections to each other that enable the organism to learn as the result of experience. Other studies show that "forgetting" may be partially the result of deterioration between neural connections, often due to disuse. So one reason why you cannot remember math as well if you haven't done it in a while is because your neurons have deteriorated that faciliated mathematical behavior. However, neurons grow more readily than they deteriorate, and deterioration may not be the only way we "forget" things.
What I suggest, and I doubt it is highly original, is that in classical conditioning and perhaps other forms of learning, when a new response is acquired in acquisition, new neural connections are made that don't deteriorate with mere extinction training. Instead, what actually happens in extinction is that you learn an inhibitory response that prevents those nerves from firing. This second response might be just some form of chemical blocking that stops neurons from responsing (perhaps I'll make a diagram). This "chemical inhibitor" is less permanent that the physical neural connections that occur in acquisition training and thus deteriorates faster. In other words, spontaneous recovery can be understood as a weaking on the strength of the chemical inhibition with the mere passage of time. Since the neurons are already connected, the mechanisms for a conditioned response are already in place and the only thing preventing its occurrence is the "chemical block." So obviously, when this chemical block weakens over time, then it can be expected that it will be less able to prevent a response from occurring, and some response may be observed.
Secondly, because the etablishment of a chemical blocking is a conditioned response in and of itself, variance from training conditions (the environmental conditions during extinction training) will result in a lessened ability to elicit the inhibitory response. This is the same principle as respondent generalization: as the characteristics of a stimulus increasing depart from those present in acquisition training, the magnitude of the response increasingly diminishes. This would seem to account for disinhibition. When a novel stimulus is presented that wasn't present in extinction training, this is a variation from the conditions in which inhibition was acquired, and thus a weaker inhibitory response in elicited, resulting in lessened ability to prevent the excitatory response.
Finally, because the neural connections are already in place and the only thing preventing their functioning is a conditioned inhibitory response, it makes sense why reaquisition occurs more rapidly with subsequent trainings. The "hardware" is already installed; it doesn't have to be built in the second time. All that has to happen is a weakening of the inhibitory response and the suppressed excitatory response will reappear. All of these seem like potential evidence for the inhibitory response theory and imply that learning occurs because of neural growth.
This is where you (finally) come in. I was thinking about it the other day, and classical conditioning has been demonstrated in unicellular microorganisms. In these organisms, obviously, there are no neurons to make connections to one another that facilitate respondent learning. This being the case, what actually happens physically within the microorganism that enables it to learn a conditioned response? I figured I'd ask you because you probably know a lot more about the physiology of unicellular organisms than most people, and you might be able to explain to me how they learn. Depending on the actual mechanisms, they may or may not be expected to show spontaneous recovery, disinhibition and rapid reaquisition. If they do, then there are serious research possibilites involving the mechanisms of inhibitory response theory. If they don't, then inhibitory responses obviously have something to do with the physiology of nerve cells and neural activity. I don't even know if protozoa have been studied for extinction or not. Perhaps respondent learning is permanent in these organisms, but I doubt it (I think they habituate according to research). Anyway, I was wondering if you could share with me your knowledge of microbiology in hopes of helping me understand the mechanics of learning processes.
I'm going to presume that you already understand the general principle of classical conditioning, US, UR, CS, CR and the like. Extinction, of course, occurs when the CS is presented repeatedly without the US and eventually fails to produce a CR. Spontaneous recovery, as you might know, is when after a period of rest from extinction, the CS is again presented alone and elicits a CR of some magnitude greater than when extinction ended. Additionally, you may remember that second, third and subsequent acquisition trainings occur more rapidly than the first or prior training. Disinhibition occurs when after a CR is extinguished, the CS is presented along with some salient, novel stimulus and the CR is again elicited.
Why am I rehearsing these things to you? Well, it's fairly obvious that extinction training does not "erase" prior aquisition training because the organism is never quite the same afterwards. Spontaneous recovery, disinhibition and rapid reacquisition all show that in some way, the organism is still different from how it was prior to initial conditioning. The general theory behind this is as follows: extinction training is not a "breaking of the US-CS association" but actually the conditioning of a second, inhibitory response. This response is more fragile and more easily disrupted than excitatory responses. It disrupts with time (spontaneous recovery) and deviations from training conditions (disinhibition). In other words, it's similar to a kind of conditioned suppression.
EDIT (FINISHING THE POST): Presumably, if we knew more about the physiology of classical conditioning, as in what physically is going on inside the organism as they learn new conditioned responses, then we might better understand why these events occur. Many studies have shown that when organisms learn new behaviors or responses, nerve growth occurs that actually creates new neural connections. In other words, neurons are making new connections to each other that enable the organism to learn as the result of experience. Other studies show that "forgetting" may be partially the result of deterioration between neural connections, often due to disuse. So one reason why you cannot remember math as well if you haven't done it in a while is because your neurons have deteriorated that faciliated mathematical behavior. However, neurons grow more readily than they deteriorate, and deterioration may not be the only way we "forget" things.
What I suggest, and I doubt it is highly original, is that in classical conditioning and perhaps other forms of learning, when a new response is acquired in acquisition, new neural connections are made that don't deteriorate with mere extinction training. Instead, what actually happens in extinction is that you learn an inhibitory response that prevents those nerves from firing. This second response might be just some form of chemical blocking that stops neurons from responsing (perhaps I'll make a diagram). This "chemical inhibitor" is less permanent that the physical neural connections that occur in acquisition training and thus deteriorates faster. In other words, spontaneous recovery can be understood as a weaking on the strength of the chemical inhibition with the mere passage of time. Since the neurons are already connected, the mechanisms for a conditioned response are already in place and the only thing preventing its occurrence is the "chemical block." So obviously, when this chemical block weakens over time, then it can be expected that it will be less able to prevent a response from occurring, and some response may be observed.
Secondly, because the etablishment of a chemical blocking is a conditioned response in and of itself, variance from training conditions (the environmental conditions during extinction training) will result in a lessened ability to elicit the inhibitory response. This is the same principle as respondent generalization: as the characteristics of a stimulus increasing depart from those present in acquisition training, the magnitude of the response increasingly diminishes. This would seem to account for disinhibition. When a novel stimulus is presented that wasn't present in extinction training, this is a variation from the conditions in which inhibition was acquired, and thus a weaker inhibitory response in elicited, resulting in lessened ability to prevent the excitatory response.
Finally, because the neural connections are already in place and the only thing preventing their functioning is a conditioned inhibitory response, it makes sense why reaquisition occurs more rapidly with subsequent trainings. The "hardware" is already installed; it doesn't have to be built in the second time. All that has to happen is a weakening of the inhibitory response and the suppressed excitatory response will reappear. All of these seem like potential evidence for the inhibitory response theory and imply that learning occurs because of neural growth.
This is where you (finally) come in. I was thinking about it the other day, and classical conditioning has been demonstrated in unicellular microorganisms. In these organisms, obviously, there are no neurons to make connections to one another that facilitate respondent learning. This being the case, what actually happens physically within the microorganism that enables it to learn a conditioned response? I figured I'd ask you because you probably know a lot more about the physiology of unicellular organisms than most people, and you might be able to explain to me how they learn. Depending on the actual mechanisms, they may or may not be expected to show spontaneous recovery, disinhibition and rapid reaquisition. If they do, then there are serious research possibilites involving the mechanisms of inhibitory response theory. If they don't, then inhibitory responses obviously have something to do with the physiology of nerve cells and neural activity. I don't even know if protozoa have been studied for extinction or not. Perhaps respondent learning is permanent in these organisms, but I doubt it (I think they habituate according to research). Anyway, I was wondering if you could share with me your knowledge of microbiology in hopes of helping me understand the mechanics of learning processes.