Pavlov s dogs

If we are to harness the placebo effect and make use of it in clinical practice, we first have to understand how it works. A number of factors have been proposed as explanations of the placebo effect. These include the relationship between doctors and patients, the patient s beliefs and expectations, the production of opiates in the brain, and a phenomenon called classical conditioning, in which people come to associate pills and injections with therapeutic effects, just as Pavlov s dogs came to associate the sound of a bell with the presentation of food. In this chapter we look at how all of these processes combine to produce placebo effects, and we consider their implications for the treatment of depression. 

The acquired or conditioned salivary reflex is elicited in response to the thought, sight, smell, or sound of food. As demonstrated with Pavlov s dog, these stimuli result in a learned response. Another stimulus that enhances salivation is nausea. Salivary secretion is inhibited by fatigue, sleep, fear, and dehydration. Overall, 1 to 2 1 of saliva may be produced per day. 

Or try to break the conditioned-response habit entirely. In a way many of us are like Pavlov s dogs, conditioned to snack when we sit in our established chair or couch and the TV goes on. To break the habit, read a book or a magazine. Don t turn the TV on at all. 

Eg, Pavlov s dog being presented with spoiled meat upon... 

Procedural (or implicit) memory is acquired through habits, perception, or movement. Recall does not require conscious attention. After several tries, a toddler takes her first step. We know that if we stand too close to a flame, we will get burned. The classical conditioning of Pavlov s dog involved a type of procedural memory (that is, for the pooch). 

The top half of Figure 7.4 depicts the sequence of stimulus-response events occurring in classical conditioning. Actually, before learning occurs, the sequence includes only three events—conditioned stimulus (CS), unconditioned stimulus (UCS), and unconditioned response (UCR). The UCS elicits a UCR automatically, as in an autonomic reflex. That is, the food (UCS) elicited a salivation reflex (UCR) in Pavlov s dogs. In the same way, the smell of popcorn (UCS) might make your mouth water (UCR), a puff of air to your eye... 

The 1897 study in which Pavlov s student substituted a glass of water for the carbon bisulphide that had been used to stimulate the dogs to salivate shows the relevance of classical conditioning to the placebo effect. The glass of water was a placebo. Although it was inert, it looked exactly like the substance that had led the dogs to salivate. 

Einally, classical conditioning is pretty well known from Pavlov s famous studies of dogs many years ago. Pavlov demonstrated that when dogs were conditioned to associate an unpleasant stimulus with one that would usually elicit no response, they learn to react to the latter response. Thus, if the sound of a bell is quickly followed by an electric shock, and this is repeated a number of times, the dogs will learn to react (yelp, say) to the sound of the bell alone. The dogs have been conditioned to associate the sound of the bell with an unpleasant experience. 

After Charles Richet had proved that acid secreted by the stomach is hydrochloric acid, he wondered whether the stomach can also secrete hydrobromic acid. He fed a dog some sodium bromide, but he could not find any bromide in the dog s gastric juice. Pavlov s collaborator, Shumova-Simanovskaya, reported in 1894 that she and Nencki had fed a dog increasing amounts of sodium bromide, for a total of 53 g in 9 days. They stated the halide concentrations in percentages to three decimal places. I have converted the values to millinormality to show the stochiometric relations between the ions that were not recognized by Shumova-Simanovskaya and Nencki. A control sample of gastric juice was 145 mN in HCl, and one of their experimental samples was 89 mN in Cr and 49 mN in Br. Bromide replaced chlo-ride. ... 

Pavlov s student V. V. Savich stimulated secretion of mucus by applying 0.2% corrosive sublimate, 10% silver nitrate, absolute alcohol or an emulsion of mustard oil to the gastric mucosa of dogs. Boris Babkin inherited his interest in mucus from Pavlov and Savich, and he and his own students stimulated mucus secretion with 1% acetic acid (ca. 160 mN) or 90% ethyl alcohol. Franklin Hollander whose devotion to mucus was as intense as Babkin s stimulated mucus secretion with topical application of water saturated with ethyl ether or with a 5% emulsion of clove oil. All those stimulants seriously damage the gastric mucosa, and their effect, other than their ability to stimulate shedding of mucus and mucus-containing cells will be discussed in a later part of this chapter. 

In Pavlov s laboratory, an esophagostomized dog with a gastric fistula began to secrete gastric juice if it were simply shown food. This psychic stimulation had been seen earlier. In 1850 Bidder and Schmidt had written It is very remarkable that simply the sight of food increases gastric secretion in a fasting animal. " ... 

Figure 4-5. Pavlov s method of constructing a vagally innervated pouch of a dog s stomach. (From Khigine PP. Activite secretoire de I estomac. Arch Soc Biol St Peters-bourg 3 461-525, 1895.)...

Long ago Sokolov, (1904...), working in Pavlov s laboratory, discovered that in the dog the introduction of 0.5 per cent HCl or of gastric juice into. .. the duodenum markedly diminished the secretion from the Pavlov pouch. ... 

The next step in Pavlov s laboratory was taken in January 1906 by Walter Gross. Once more, Pavlov performed the operation on a dog, first preparing it in the same way he had for Lonnqvist. Gross found, as Lonnqvist had, that insertion of food substances, and in particular meat extract, into the stomach through the... 

It is not clear which of Pavlov s students did the next experiments. Babkin gave references to dissertations in Russian, but he did not specify which contained what information. " Babkin did summarize the work in 1934 when he himself was beginning to think that histamine is responsible for the chemical phase of gastric secretion. " In any event, the step was Pavlov s, for it was he who made a pouch of the pyloric antrum in a dog that also had a gastric fistula and a gastroenterostomy (Fig. 6-1C). Then, [ijntroduction of different chemical substances, such as meat extract, soap, etc. into an isolated and non-denervated, or even into a denervated pyloric pouch, caused flow of gastric juice from the fundus. " ... 

Pavlov said that when he collected pure gastric juice from a vagally innervated pouch of a dog s stomach, he saw that it is a rule almost without exception that the acidity of the juice is closely dependent upon the rate of secretion the more rapid the latter, the more acid is the juice and vice... 

Figure 3-9. Boris Babkin s determination of the effect of introduction of 1% acetic acid (H Ac) into the main stomach of a dog upon the secretory response of the dog s Pavlov pouch to sham feeding. (From Babkin BP, Hebb CO, Krueger L. Changes in the secretory activity of gastric glands resulting from the application of acetic acid solutions to the gastric mucosa. Q / Exp Physiol 31 63-77, 1941.)...

Figure 4-1. Volume (Menge), acidity (Aziditat), and egg white digestion (Eiweissver-dauung) of gastric juice secreted by a dog s Pavlov pouch in response to sham feeding. Each vertical line marks a 5-minute interval. At X the dog was shown a cat. (From Bickel A. Experimentelle Untersuchungen uber den Einfluss von Affekten auf die Magensaftsekretion. Dtsch Med Wochenschr 3 829- 83, 1905.)...

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