Few areas of neurobehavioral research seemed more promising in the early sixties than that investigating the relationship between protein synthesis and learning. The conceptual framework for this research was derived directly from molecular biology, which had shown that genetic information is stored in nucleic acids and expressed in proteins. Why not acquired information as well?
The first step toward establishing a connection between protein synthesis and learning seemed to be block memory (cause amnesia) by interrupting the production of protein. We were fortunate in finding a nonlethal dosage of puromycin that could, it first appeared, thoroughly inhibit brain protein synthesis as well as reliably produce amnesia.
Before the actual connection between protein synthesis and learning could be established, however, we began to have doubts about whether inhibition of protein synthesis was in fact the method by which puromycin produced amnesia. First, other drugs, glutarimides—themselves potent protein-synthesis inhibitors—either failed to cause amnesia in some situations where it could easily be induced by puromycin or produced an amnesia with a different time course from that of puromycin. Second, puromycin was found to inhibit protein synthesis by breaking certain amino-acid chains, and the resulting fragments were suspected of being the actual cause of amnesia in some cases. Third, puromycin was reported to cause abnormalities in the brain, including seizures. Thus, not only were decreased protein synthesis and amnesia dissociated, but alternative mechanisms for the amnestic action of puromycin were readily suggested.
So, puromycin turned out to be a disappointment. It came to be regarded as a poor agent for amnesia studies, although, of course, it was poor only in the context of our original paradigm of protein-synthesis inhibition. In our frustration, our initial response was simply to change drugs rather than our conceptual orientation. After many such disappointments, however, it now appears unlikely that we will make a firm connection between protein synthesis and learning merely by pursuing the approaches of the past. Our experience with drugs has shown that all the amnestic agents often interfere with memory in ways that seem unrelated to their inhibition of protein synthesis. More importantly, the notion that the interruption or intensification of protein production in the brain can be related in cause-and-effect fashion to learning now seems simplistic and unproductive. Remove the battery from a car and the car will not go. Drive the car a long distance at high speed and the battery will become more highly charged. Neither of these facts proves that the battery powers the car; only a knowledge of the overall automotive system will reveal its mechanism of the locomotion and the role of the battery within that system.
21. This passage was most likely excerpted from
(A) a diary kept by a practicing neurobehavioral researcher
(B) a newspaper article on recent advances in the biochemistry of learning
(C) a technical article on experimental techniques in the field of molecular biology
(D) an article summarizing a series of scientific investigations in neurobehavioral research
(E) a book review in a leading journal devoted to genetic research
22. The primary purpose of the passage is to show that extensive experimentation has
(A) demonstrated the importance of amino-acid fragmentation in the induction of amnesia
(B) cast doubt on the value of puromycin in the neurobehavioral investigation of learning
(C) revealed the importance of amnesia in the neurobehavioral study of learning
(D) not yet demonstrated the applicability of molecular biology to neurobehavioral research
(E) not supported the hypothesis that learning is directly dependent on protein synthesis
23. According to the passage, neurobehaviorists initially based their belief that protein synthesis was related to learning on which of the following?
(A) Traditional theories about learning
(B) New techniques in protein synthesis
(C) Previous discoveries in molecular biology
(D) Specific research into learning and amnesia
(E) Historic experiments on the effects of puromycin
24. The passage mentions all of the following as effects of puromycin EXCEPT:
(A) brain seizures
(B) memory loss
(C) inhibition of protein synthesis
(D) destruction of genetic information
(E) fragmentation of amino-acid chains
25. It can be inferred from the passage that, after puromycin was perceived to be a disappointment, researchers did which of the following?
(A) They ceased to experiment with puromycin and shifted to other promising protein-synthesis inhibitors.
(B) They ceased to experiment with puromycin, and reexamined through experiments the relationship between genetic information and acquired information.
(C) The continued to experiment with puromycin, but applied their results to other facets of memory research.
(D) They continued to experiment with puromycin, but also tried other protein-synthesis inhibitors.
(E) They continued to experiment with puromycin until a new neuroanatomical framework was developed.
26. In the example of the car (lines 58-65), the battery is meant to represent which of the following elements in the neurobehavioral research program?
(D) Protein synthesis
(E) Acquired information
27. Which of the following statements could be most likely to come after the last sentence of the passage?
(A) The failures of the past, however, must not impede further research into the amnestic action of protein-synthesis inhibitors.
(B) It is a legacy of this research, therefore, that molecular biology’s genetic models have led to disagreements among neurobehaviorists.
(C) The ambivalent status of current research, however, should not deter neurobehaviorists from exploring the deeper connections between protein production and learning.
(D) It is important in the future, therefore, for behavioral biochemists to emphasize more strongly the place of their specific findings within the overall protein-synthesis model of learning.
(E) It is important in the future, therefore, for behavioral biochemists to focus on the several components of the total learning system.